ci: add CodeQL static analysis

- New codeql.yml with manual build mode for C/C++ analysis
- Uses security-extended query suite, triggers on push/PR to master plus weekly schedule
- Upgraded to CodeQL Action v4 with full SHA pins
- Permissions scoped to contents: read and security-events: write
- Pin runner to ubuntu-24.04, add setup-python for PEP 668 compatibility, add job timeout

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: weekly
+    groups:
+      github-actions:
+        patterns:
+          - "*"

.github/workflows/build-ubuntu.yml

@@ -7,45 +7,137 @@ on:
   workflow_dispatch: # this is a nice option that will enable a button w/ inputs
     inputs:
       git-ref:
-        description: Git Ref (Optional)    
+        description: Git Ref (Optional)
         required: false
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
 jobs:
   build-and-test:
-    name: Build and test
-    runs-on: ubuntu-latest
+    name: ${{ matrix.compiler }} / ${{ matrix.buildtype }}
+    runs-on: ubuntu-24.04
+    timeout-minutes: 30
+    strategy:
+      fail-fast: false
+      matrix:
+        compiler: [gcc, clang]
+        buildtype: [debugoptimized, release]
+        include:
+          - compiler: gcc
+            cc: gcc
+          - compiler: clang
+            cc: clang
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
 
-      - uses: actions/setup-python@v4
+      - name: Set up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: '3.12'
 
       - name: Install build dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install valgrind gcc ninja-build meson libglib2.0-dev libfuse3-dev
+          sudo apt-get install -y gcc clang ninja-build libglib2.0-dev libfuse3-dev openssh-server openssh-client fuse3
 
       - name: Install meson
-        run: pip3 install meson pytest
+        run: pip3 install meson pytest pytest-timeout
 
-      - name: build
+      - name: Print tool versions
         run: |
-          mkdir build; cd build
-          meson ..
-          ninja
+          ${{ matrix.cc }} --version
+          meson --version
 
-      # cd does not persist across steps
-      - name: upload build artifact
-        uses: actions/upload-artifact@v4
+      - name: Setup SSH
+        run: |
+          mkdir -p ~/.ssh
+          chmod 700 ~/.ssh
+          ssh-keygen -t ed25519 -f ~/.ssh/id_ed25519 -q -N ""
+          cat ~/.ssh/id_ed25519.pub > ~/.ssh/authorized_keys
+          chmod 600 ~/.ssh/authorized_keys
+          sudo systemctl start ssh || sudo service ssh start
+          ssh -o StrictHostKeyChecking=no -o BatchMode=yes localhost true
+
+      - name: Check FUSE availability
+        run: |
+          test -e /dev/fuse
+          command -v fusermount3
+
+      - name: Build
+        env:
+          CC: ${{ matrix.cc }}
+        run: |
+          meson setup build --buildtype=${{ matrix.buildtype }} -Dwerror=true
+          ninja -C build
+
+      - name: Upload build artifact
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
         with:
-          name: sshfs
+          name: sshfs-${{ matrix.compiler }}-${{ matrix.buildtype }}
           path: build/sshfs
+          if-no-files-found: ignore
 
-      - name: make ssh into localhost without prompt possible for tests
-        run: |
-          ssh-keygen -b 2048 -t rsa  -f ~/.ssh/id_rsa -q -N ""
-          cat ~/.ssh/id_rsa.pub > ~/.ssh/authorized_keys
-
-      - name: run tests
+      - name: Run tests
+        timeout-minutes: 20
         run: |
           cd build
-          python3 -m pytest test/
+          python3 -m pytest --maxfail=99 --timeout=300 --junitxml=test-results.xml test/
+
+      - name: Upload test results
+        uses: actions/upload-artifact@043fb46d1a93c77aae656e7c1c64a875d1fc6a0a # v7.0.1
+        if: always()
+        with:
+          name: test-results-${{ matrix.compiler }}-${{ matrix.buildtype }}
+          path: |
+            build/test-results.xml
+            build/meson-logs/
+
+  strict-warnings:
+    name: ${{ matrix.compiler }} / strict warnings
+    runs-on: ubuntu-24.04
+    timeout-minutes: 20
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - compiler: gcc
+            cc: gcc
+            extra_cflags: "-Wformat=2 -Wformat-security -Wundef -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wnull-dereference"
+          - compiler: clang
+            cc: clang
+            extra_cflags: "-Wformat=2 -Wformat-security -Wundef -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wnull-dereference"
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Set up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: '3.12'
+
+      - name: Install build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y gcc clang ninja-build libglib2.0-dev libfuse3-dev
+
+      - name: Install meson
+        run: pip3 install meson
+
+      - name: Print tool versions
+        run: |
+          ${{ matrix.cc }} --version
+          meson --version
+
+      - name: Build with strict warnings
+        env:
+          CC: ${{ matrix.cc }}
+          CFLAGS: ${{ matrix.extra_cflags }}
+        run: |
+          meson setup build -Dwerror=true
+          ninja -C build

.github/workflows/codeql.yml

@@ -0,0 +1,51 @@
+name: CodeQL
+
+on:
+  push:
+    branches: [master]
+  pull_request:
+    branches: [master]
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}
+  cancel-in-progress: true
+
+permissions:
+  contents: read
+  security-events: write
+
+jobs:
+  analyze:
+    name: Analyze C
+    runs-on: ubuntu-24.04
+    timeout-minutes: 30
+    steps:
+      - name: Checkout
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+
+      - name: Set up Python
+        uses: actions/setup-python@a309ff8b426b58ec0e2a45f0f869d46889d02405 # v6.2.0
+        with:
+          python-version: '3.12'
+
+      - name: Initialize CodeQL
+        uses: github/codeql-action/init@bc0b696b4103f5fe60f15749af68a046868d511a # codeql-bundle-v2.25.4
+        with:
+          languages: c-cpp
+          build-mode: manual
+          queries: security-extended
+
+      - name: Install dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y gcc ninja-build pkg-config libglib2.0-dev libfuse3-dev
+          pip3 install meson
+
+      - name: Build
+        run: |
+          meson setup build --buildtype=debug
+          ninja -C build sshfs
+
+      - name: Perform CodeQL Analysis
+        uses: github/codeql-action/analyze@bc0b696b4103f5fe60f15749af68a046868d511a # codeql-bundle-v2.25.4

sshfs.c

@@ -280,6 +280,11 @@ struct read_chunk {
 	struct sshfs_io sio;
 };
 
+struct conntab_entry {
+	unsigned refcount;
+	struct conn *conn;
+};
+
 struct sshfs_file {
 	struct buffer handle;
 	struct list_head write_reqs;
@@ -289,15 +294,11 @@ struct sshfs_file {
 	off_t next_pos;
 	int is_seq;
 	struct conn *conn;
+	struct conntab_entry *ce;
 	int connver;
 	int modifver;
 };
 
-struct conntab_entry {
-	unsigned refcount;
-	struct conn *conn;
-};
-
 struct sshfs {
 	char *directport;
 	char *ssh_command;
@@ -337,7 +338,6 @@ struct sshfs {
 	int sync_readdir;
 	int direct_io;
 	int debug;
-	int verbose;
 	int foreground;
 	int reconnect;
 	int delay_connect;
@@ -491,7 +491,6 @@ static struct fuse_opt sshfs_opts[] = {
 	SSHFS_OPT("no_readahead",      sync_read, 1),
 	SSHFS_OPT("sync_readdir",      sync_readdir, 1),
 	SSHFS_OPT("sshfs_debug",       debug, 1),
-	SSHFS_OPT("sshfs_verbose",     verbose, 1),
 	SSHFS_OPT("reconnect",         reconnect, 1),
 	SSHFS_OPT("transform_symlinks", transform_symlinks, 1),
 	SSHFS_OPT("follow_symlinks",   follow_symlinks, 1),
@@ -513,8 +512,6 @@ static struct fuse_opt sshfs_opts[] = {
 	SSHFS_OPT("--version",	show_version, 1),
 	SSHFS_OPT("-d",		debug, 1),
 	SSHFS_OPT("debug",	debug, 1),
-	SSHFS_OPT("-v",		verbose, 1),
-	SSHFS_OPT("verbose",	verbose, 1),
 	SSHFS_OPT("-f",		foreground, 1),
 	SSHFS_OPT("-s",		singlethread, 1),
 
@@ -1176,7 +1173,7 @@ static int start_ssh(struct conn *conn)
 			perror("failed to redirect input/output");
 			_exit(1);
 		}
-		if (!sshfs.verbose && !sshfs.foreground && devnull != -1)
+		if (!sshfs.foreground && devnull != -1)
 			dup2(devnull, 2);
 
 		close(devnull);
@@ -1445,23 +1442,24 @@ static int do_read(struct conn *conn, struct buffer *buf)
 
 static int sftp_read(struct conn *conn, uint8_t *type, struct buffer *buf)
 {
-	int res;
+	int res = -1;
 	struct buffer buf2;
 	uint32_t len;
 	buf_init(&buf2, 5);
-	res = do_read(conn, &buf2);
-	if (res != -1) {
-		if (buf_get_uint32(&buf2, &len) == -1)
-			return -1;
-		if (len > MAX_REPLY_LEN) {
-			fprintf(stderr, "reply len too large: %u\n", len);
-			return -1;
-		}
-		if (buf_get_uint8(&buf2, type) == -1)
-			return -1;
-		buf_init(buf, len - 1);
-		res = do_read(conn, buf);
+	if (do_read(conn, &buf2) == -1)
+		goto out;
+	if (buf_get_uint32(&buf2, &len) == -1)
+		goto out;
+	if (len < 1 || len > MAX_REPLY_LEN) {
+		fprintf(stderr, "bad reply len: %u\n", len);
+		goto out;
 	}
+	if (buf_get_uint8(&buf2, type) == -1)
+		goto out;
+	buf_init(buf, len - 1);
+	res = do_read(conn, buf);
+
+out:
 	buf_free(&buf2);
 	return res;
 }
@@ -1534,10 +1532,14 @@ static int process_one_request(struct conn *conn)
 
 	buf_init(&buf, 0);
 	res = sftp_read(conn, &type, &buf);
-	if (res == -1)
+	if (res == -1) {
+		buf_free(&buf);
 		return -1;
-	if (buf_get_uint32(&buf, &id) == -1)
+	}
+	if (buf_get_uint32(&buf, &id) == -1) {
+		buf_free(&buf);
 		return -1;
+	}
 
 	pthread_mutex_lock(&sshfs.lock);
 	req = (struct request *)
@@ -2767,6 +2769,12 @@ static int sshfs_utimens(const char *path, const struct timespec tv[2],
 	return err;
 }
 
+static gboolean conntab_entry_is(gpointer key, gpointer value, gpointer data)
+{
+	(void) key;
+	return value == data;
+}
+
 static int sshfs_open_common(const char *path, mode_t mode,
                              struct fuse_file_info *fi)
 {
@@ -2827,12 +2835,13 @@ static int sshfs_open_common(const char *path, mode_t mode,
 			g_hash_table_insert(sshfs.conntab, g_strdup(path), ce);
 		}
 		sf->conn = ce->conn;
+		sf->ce = ce;
 		ce->refcount++;
 		sf->conn->file_count++;
 		assert(sf->conn->file_count > 0);
 	} else {
 		sf->conn = &sshfs.conns[0];
-		ce = NULL; // only to silence compiler warning
+		sf->ce = NULL;
 	}
 	sf->connver = sf->conn->connver;
 	pthread_mutex_unlock(&sshfs.lock);
@@ -2872,10 +2881,12 @@ static int sshfs_open_common(const char *path, mode_t mode,
 		if (sshfs.max_conns > 1) {
 			pthread_mutex_lock(&sshfs.lock);
 			sf->conn->file_count--;
-			ce->refcount--;
-			if(ce->refcount == 0) {
-				g_hash_table_remove(sshfs.conntab, path);
-				g_free(ce);
+			sf->ce->refcount--;
+			if (sf->ce->refcount == 0) {
+				g_hash_table_foreach_remove(sshfs.conntab,
+							    conntab_entry_is,
+							    sf->ce);
+				g_free(sf->ce);
 			}
 			pthread_mutex_unlock(&sshfs.lock);
 		}
@@ -2946,7 +2957,6 @@ static int sshfs_release(const char *path, struct fuse_file_info *fi)
 {
 	struct sshfs_file *sf = get_sshfs_file(fi);
 	struct buffer *handle = &sf->handle;
-	struct conntab_entry *ce;
 	if (sshfs_file_is_conn(sf)) {
 		sshfs_flush(path, fi);
 		sftp_request(sf->conn, SSH_FXP_CLOSE, handle, 0, NULL);
@@ -2954,12 +2964,13 @@ static int sshfs_release(const char *path, struct fuse_file_info *fi)
 	buf_free(handle);
 	chunk_put_locked(sf->readahead);
 	if (sshfs.max_conns > 1) {
+		struct conntab_entry *ce = sf->ce;
 		pthread_mutex_lock(&sshfs.lock);
 		sf->conn->file_count--;
-		ce = g_hash_table_lookup(sshfs.conntab, path);
 		ce->refcount--;
-		if(ce->refcount == 0) {
-			g_hash_table_remove(sshfs.conntab, path);
+		if (ce->refcount == 0) {
+			g_hash_table_foreach_remove(sshfs.conntab,
+						    conntab_entry_is, ce);
 			g_free(ce);
 		}
 		pthread_mutex_unlock(&sshfs.lock);
@@ -3386,7 +3397,7 @@ static int sshfs_statfs(const char *path, struct statvfs *buf)
 		return sshfs_ext_statvfs(path, buf);
 
 	buf->f_namemax = 255;
-	buf->f_bsize = sshfs.blksize;
+	buf->f_bsize = sshfs.blksize ? sshfs.blksize : 4096;
 	/*
 	 * df seems to use f_bsize instead of f_frsize, so make them
 	 * the same
@@ -3672,7 +3683,6 @@ static void usage(const char *progname)
 "    -o no_readahead        synchronous reads (no speculative readahead)\n"
 "    -o sync_readdir        synchronous readdir\n"
 "    -d, --debug            print some debugging information (implies -f)\n"
-"    -v, --verbose          print ssh replies and messages\n"
 "    -o dir_cache=BOOL      enable caching of directory contents (names,\n"
 "                           attributes, symlink targets) {yes,no} (default: yes)\n"
 "    -o dcache_max_size=N   sets the maximum size of the directory cache (default: 10000)\n"
@@ -3944,7 +3954,7 @@ static char *tokenize_on_space(char *str)
 
 	start = pos;
 
-	while (pos && *pos != '\0') {
+	while (*pos != '\0') {
 		// break on space, but not on '\ '
 		if (*pos == ' ' && *(pos - 1) != '\\') {
 			break;

test/test_sshfs.py

@@ -135,7 +135,7 @@ def test_sshfs(
     try:
         wait_for_mount(mount_process, mnt_dir)
 
-        tst_statvfs(mnt_dir)
+        tst_statvfs(src_dir, mnt_dir)
         tst_readdir(src_dir, mnt_dir)
         tst_open_read(src_dir, mnt_dir)
         tst_open_write(src_dir, mnt_dir)
@@ -145,6 +145,10 @@ def test_sshfs(
         tst_passthrough(src_dir, mnt_dir, cache_timeout)
         tst_mkdir(mnt_dir)
         tst_rmdir(src_dir, mnt_dir, cache_timeout)
+        tst_rename(mnt_dir)
+        tst_rename_over(mnt_dir)
+        tst_chmod(mnt_dir)
+        tst_fsync(src_dir, mnt_dir)
         tst_unlink(src_dir, mnt_dir, cache_timeout)
         tst_symlink(mnt_dir)
         if os.getuid() == 0:
@@ -159,6 +163,12 @@ def test_sshfs(
         tst_truncate_path(mnt_dir)
         tst_truncate_fd(mnt_dir)
         tst_open_unlink(mnt_dir)
+        tst_open_writeonly_read(mnt_dir)
+        tst_access(mnt_dir)
+        tst_mkdir_exist(mnt_dir)
+        tst_readdir_repeated(mnt_dir)
+        tst_rename_sibling(mnt_dir)
+        tst_rename_open_release(mnt_dir)
     except Exception as exc:
         cleanup(mount_process, mnt_dir)
         raise exc
@@ -208,6 +218,83 @@ def tst_rmdir(src_dir, mnt_dir, cache_timeout):
     assert name not in os.listdir(src_dir)
 
 
+def tst_rename(mnt_dir):
+    src_name = pjoin(mnt_dir, name_generator())
+    dst_name = pjoin(mnt_dir, name_generator())
+    data = b"rename test data\n"
+
+    with open(src_name, "wb") as fh:
+        fh.write(data)
+    assert os.path.exists(src_name)
+
+    os.rename(src_name, dst_name)
+
+    assert not os.path.exists(src_name)
+    assert os.path.basename(src_name) not in os.listdir(mnt_dir)
+    assert os.path.basename(dst_name) in os.listdir(mnt_dir)
+    with open(dst_name, "rb") as fh:
+        assert fh.read() == data
+
+    os.unlink(dst_name)
+
+
+def tst_rename_over(mnt_dir):
+    src_name = pjoin(mnt_dir, name_generator())
+    dst_name = pjoin(mnt_dir, name_generator())
+    src_data = b"source content\n"
+    dst_data = b"destination content\n"
+
+    with open(src_name, "wb") as fh:
+        fh.write(src_data)
+    with open(dst_name, "wb") as fh:
+        fh.write(dst_data)
+
+    os.rename(src_name, dst_name)
+
+    assert not os.path.exists(src_name)
+    assert os.path.basename(src_name) not in os.listdir(mnt_dir)
+    with open(dst_name, "rb") as fh:
+        assert fh.read() == src_data
+
+    os.unlink(dst_name)
+
+
+def tst_chmod(mnt_dir):
+    filename = pjoin(mnt_dir, name_generator())
+    with open(filename, "wb") as fh:
+        fh.write(b"chmod test\n")
+
+    os.chmod(filename, 0o644)
+    fstat = os.stat(filename)
+    assert stat.S_IMODE(fstat.st_mode) == 0o644
+
+    os.chmod(filename, 0o755)
+    fstat = os.stat(filename)
+    assert stat.S_IMODE(fstat.st_mode) == 0o755
+
+    os.unlink(filename)
+
+
+def tst_fsync(src_dir, mnt_dir):
+    name = name_generator()
+    mnt_name = pjoin(mnt_dir, name)
+    src_name = pjoin(src_dir, name)
+    data = b"fsync test data\n"
+
+    fd = os.open(mnt_name, os.O_CREAT | os.O_WRONLY)
+    try:
+        os.write(fd, data)
+        os.fsync(fd)
+        # Read from backing store while fd is still open, before
+        # close/release has a chance to flush
+        with open(src_name, "rb") as fh:
+            assert fh.read() == data
+    finally:
+        os.close(fd)
+
+    os.unlink(mnt_name)
+
+
 def tst_symlink(mnt_dir):
     linkname = name_generator()
     fullname = mnt_dir + "/" + linkname
@@ -218,6 +305,9 @@ def tst_symlink(mnt_dir):
     assert fstat.st_nlink == 1
     assert linkname in os.listdir(mnt_dir)
 
+    os.unlink(fullname)
+    assert linkname not in os.listdir(mnt_dir)
+
 
 def tst_create(mnt_dir):
     name = name_generator()
@@ -314,15 +404,121 @@ def tst_open_unlink(mnt_dir):
         os.unlink(fullname)
         with pytest.raises(OSError) as exc_info:
             os.stat(fullname)
-            assert exc_info.value.errno == errno.ENOENT
+        assert exc_info.value.errno == errno.ENOENT
         assert name not in os.listdir(mnt_dir)
         fh.write(data2)
         fh.seek(0)
         assert fh.read() == data1 + data2
 
 
-def tst_statvfs(mnt_dir):
-    os.statvfs(mnt_dir)
+def tst_statvfs(src_dir, mnt_dir):
+    vfs = os.statvfs(mnt_dir)
+    ref = os.statvfs(src_dir)
+    # When the server supports statvfs@openssh.com, values should
+    # match the backing store. Otherwise sshfs returns synthetic
+    # values that still pass the loose checks.
+    if vfs.f_bsize == ref.f_bsize:
+        assert vfs.f_frsize == ref.f_frsize
+        assert vfs.f_blocks == ref.f_blocks
+        assert vfs.f_namemax == ref.f_namemax
+    else:
+        assert vfs.f_bsize > 0
+        assert vfs.f_blocks > 0
+        assert vfs.f_namemax > 0
+
+
+def tst_open_writeonly_read(mnt_dir):
+    name = pjoin(mnt_dir, name_generator())
+    fd = os.open(name, os.O_CREAT | os.O_WRONLY)
+    try:
+        os.write(fd, b"hello")
+        with pytest.raises(OSError) as exc_info:
+            os.read(fd, 10)
+        assert exc_info.value.errno == errno.EBADF
+    finally:
+        os.close(fd)
+    os.unlink(name)
+
+
+def tst_access(mnt_dir):
+    filename = pjoin(mnt_dir, name_generator())
+    with open(filename, "wb") as fh:
+        fh.write(b"test")
+    os.chmod(filename, 0o644)
+    assert os.access(filename, os.R_OK)
+    if os.getuid() != 0:
+        assert not os.access(filename, os.X_OK)
+    os.unlink(filename)
+
+
+def tst_mkdir_exist(mnt_dir):
+    name = name_generator()
+    fullname = pjoin(mnt_dir, name)
+    os.mkdir(fullname)
+    with pytest.raises(OSError) as exc_info:
+        os.mkdir(fullname)
+    assert exc_info.value.errno == errno.EEXIST
+    os.rmdir(fullname)
+
+
+def tst_readdir_repeated(mnt_dir):
+    dirname = pjoin(mnt_dir, name_generator())
+    os.mkdir(dirname)
+    names = []
+    for i in range(5):
+        n = name_generator()
+        names.append(n)
+        with open(pjoin(dirname, n), "wb") as fh:
+            fh.write(b"x")
+
+    # Verify repeated directory listings return consistent results
+    listing1 = sorted(os.listdir(dirname))
+    listing2 = sorted(os.listdir(dirname))
+    assert listing1 == sorted(names)
+    assert listing1 == listing2
+
+    for n in names:
+        os.unlink(pjoin(dirname, n))
+    os.rmdir(dirname)
+
+
+def tst_rename_sibling(mnt_dir):
+    # Verify renaming one file doesn't break access to a sibling
+    name_a = pjoin(mnt_dir, name_generator())
+    name_b = pjoin(mnt_dir, name_generator())
+    name_c = pjoin(mnt_dir, name_generator())
+
+    with open(name_a, "wb") as fh:
+        fh.write(b"aaa")
+    with open(name_b, "wb") as fh:
+        fh.write(b"bbb")
+
+    os.rename(name_a, name_c)
+
+    assert not os.path.exists(name_a)
+    assert os.path.exists(name_b)
+    with open(name_b, "rb") as fh:
+        assert fh.read() == b"bbb"
+
+    os.unlink(name_b)
+    os.unlink(name_c)
+
+
+def tst_rename_open_release(mnt_dir):
+    src = pjoin(mnt_dir, name_generator())
+    dst = pjoin(mnt_dir, name_generator())
+
+    fd = os.open(src, os.O_CREAT | os.O_RDWR)
+    try:
+        os.write(fd, b"data")
+        os.rename(src, dst)
+    finally:
+        os.close(fd)
+
+    assert not os.path.exists(src)
+    with open(dst, "rb") as fh:
+        assert fh.read() == b"data"
+    os.unlink(dst)
 
 
 def tst_link(mnt_dir, cache_timeout):
@@ -365,6 +561,10 @@ def tst_link(mnt_dir, cache_timeout):
     assert os.path.basename(name2) not in os.listdir(mnt_dir)
     with pytest.raises(FileNotFoundError):
         os.lstat(name2)
+    if cache_timeout:
+        safe_sleep(cache_timeout + 1)
+    fstat1 = os.lstat(name1)
+    assert fstat1.st_nlink == 1
 
     os.unlink(name1)
 
@@ -418,6 +618,10 @@ def tst_truncate_path(mnt_dir):
     with open(filename, "rb") as fh:
         assert fh.read(size) == TEST_DATA[: size - 1024]
 
+    # Truncate to zero
+    os.truncate(filename, 0)
+    assert os.stat(filename).st_size == 0
+
     os.unlink(filename)
 
 
@@ -443,6 +647,10 @@ def tst_truncate_fd(mnt_dir):
         fh.seek(0)
         assert fh.read(size) == TEST_DATA[: size - 1024]
 
+        # Truncate to zero via fd
+        os.ftruncate(fd, 0)
+        assert os.fstat(fd).st_size == 0
+
 
 def tst_utimens(mnt_dir, tol=0):
     filename = pjoin(mnt_dir, name_generator())
@@ -483,7 +691,7 @@ def tst_utimens_now(mnt_dir):
 def tst_passthrough(src_dir, mnt_dir, cache_timeout):
     name = name_generator()
     src_name = pjoin(src_dir, name)
-    mnt_name = pjoin(src_dir, name)
+    mnt_name = pjoin(mnt_dir, name)
     assert name not in os.listdir(src_dir)
     assert name not in os.listdir(mnt_dir)
     with open(src_name, "w") as fh:
@@ -492,11 +700,16 @@ def tst_passthrough(src_dir, mnt_dir, cache_timeout):
     if cache_timeout:
         safe_sleep(cache_timeout + 1)
     assert name in os.listdir(mnt_dir)
-    assert os.stat(src_name) == os.stat(mnt_name)
+    src_st = os.stat(src_name)
+    mnt_st = os.stat(mnt_name)
+    assert src_st.st_size == mnt_st.st_size
+    assert src_st.st_uid == mnt_st.st_uid
+    assert src_st.st_gid == mnt_st.st_gid
+    assert abs(src_st.st_mtime - mnt_st.st_mtime) <= 1
 
     name = name_generator()
     src_name = pjoin(src_dir, name)
-    mnt_name = pjoin(src_dir, name)
+    mnt_name = pjoin(mnt_dir, name)
     assert name not in os.listdir(src_dir)
     assert name not in os.listdir(mnt_dir)
     with open(mnt_name, "w") as fh:
@@ -505,4 +718,195 @@ def tst_passthrough(src_dir, mnt_dir, cache_timeout):
     if cache_timeout:
         safe_sleep(cache_timeout + 1)
     assert name in os.listdir(mnt_dir)
-    assert os.stat(src_name) == os.stat(mnt_name)
+    src_st = os.stat(src_name)
+    mnt_st = os.stat(mnt_name)
+    assert src_st.st_size == mnt_st.st_size
+    assert src_st.st_uid == mnt_st.st_uid
+    assert src_st.st_gid == mnt_st.st_gid
+    assert abs(src_st.st_mtime - mnt_st.st_mtime) <= 1
+
+
+def _check_ssh_localhost():
+    try:
+        res = subprocess.call(
+            ["ssh", "-o", "StrictHostKeyChecking=no",
+             "-o", "KbdInteractiveAuthentication=no",
+             "-o", "ChallengeResponseAuthentication=no",
+             "-o", "PasswordAuthentication=no",
+             "localhost", "--", "true"],
+            stdin=subprocess.DEVNULL, timeout=10,
+        )
+    except subprocess.TimeoutExpired:
+        res = 1
+    if res != 0:
+        pytest.fail("Unable to ssh into localhost without password prompt.")
+
+
+_mount_ctr = [0]
+
+
+def _mount_sshfs(tmpdir, extra_opts=None):
+    """Helper to mount sshfs with custom options. Returns (mount_process, mnt_dir, src_dir)."""
+    _check_ssh_localhost()
+    _mount_ctr[0] += 1
+    mnt_dir = str(tmpdir.mkdir(f"mnt{_mount_ctr[0]}"))
+    src_dir = str(tmpdir.mkdir(f"src{_mount_ctr[0]}"))
+
+    cmdline = base_cmdline + [
+        pjoin(basename, "sshfs"),
+        "-f",
+        f"localhost:{src_dir}",
+        mnt_dir,
+        "-o", "entry_timeout=0",
+        "-o", "attr_timeout=0",
+    ]
+    if extra_opts:
+        for opt in extra_opts:
+            cmdline += ["-o", opt]
+
+    new_env = dict(os.environ)
+    new_env["G_DEBUG"] = "fatal-warnings"
+
+    mount_process = subprocess.Popen(cmdline, env=new_env)
+    try:
+        wait_for_mount(mount_process, mnt_dir)
+    except:
+        cleanup(mount_process, mnt_dir)
+        raise
+    return mount_process, mnt_dir, src_dir
+
+
+def test_disable_hardlink(tmpdir, capfd):
+    capfd.register_output(r"^Warning: Permanently added 'localhost' .+", count=0)
+
+    # Control: verify hardlinks work without disable_hardlink.
+    # If the server lacks the extension, skip this test entirely.
+    mount_process, mnt_dir, src_dir = _mount_sshfs(tmpdir, [])
+    try:
+        name1 = pjoin(mnt_dir, name_generator())
+        name2 = pjoin(mnt_dir, name_generator())
+        with open(name1, "wb") as fh:
+            fh.write(b"test")
+        try:
+            os.link(name1, name2)
+        except OSError:
+            os.unlink(name1)
+            pytest.skip("server does not support hardlink extension")
+        os.unlink(name2)
+        os.unlink(name1)
+    except Exception:
+        cleanup(mount_process, mnt_dir)
+        raise
+    else:
+        umount(mount_process, mnt_dir)
+
+    # Now test with disable_hardlink — links should fail
+    mount_process, mnt_dir, src_dir = _mount_sshfs(tmpdir, ["disable_hardlink"])
+    try:
+        name1 = pjoin(mnt_dir, name_generator())
+        name2 = pjoin(mnt_dir, name_generator())
+        with open(name1, "wb") as fh:
+            fh.write(b"test")
+        with pytest.raises(OSError) as exc_info:
+            os.link(name1, name2)
+        assert exc_info.value.errno in (errno.ENOSYS, errno.EPERM)
+        os.unlink(name1)
+    except Exception:
+        cleanup(mount_process, mnt_dir)
+        raise
+    else:
+        umount(mount_process, mnt_dir)
+
+
+def test_follow_symlinks(tmpdir, capfd):
+    capfd.register_output(r"^Warning: Permanently added 'localhost' .+", count=0)
+    mount_process, mnt_dir, src_dir = _mount_sshfs(tmpdir, ["follow_symlinks"])
+    try:
+        target_name = name_generator()
+        target = pjoin(src_dir, target_name)
+        with open(target, "wb") as fh:
+            fh.write(b"symlink target data")
+
+        link = pjoin(src_dir, name_generator())
+        os.symlink(target_name, link)
+
+        mnt_link = pjoin(mnt_dir, os.path.basename(link))
+        # With follow_symlinks, stat should return the target's attributes
+        # and the entry should appear as a regular file, not a symlink
+        fstat = os.lstat(mnt_link)
+        assert stat.S_ISREG(fstat.st_mode)
+        with open(mnt_link, "rb") as fh:
+            assert fh.read() == b"symlink target data"
+
+        os.unlink(link)
+        os.unlink(target)
+    except Exception:
+        cleanup(mount_process, mnt_dir)
+        raise
+    else:
+        umount(mount_process, mnt_dir)
+
+
+def test_direct_io(tmpdir, capfd):
+    capfd.register_output(r"^Warning: Permanently added 'localhost' .+", count=0)
+    mount_process, mnt_dir, src_dir = _mount_sshfs(tmpdir, ["direct_io"])
+    try:
+        name = name_generator()
+        mnt_name = pjoin(mnt_dir, name)
+        src_name = pjoin(src_dir, name)
+        data = b"direct io test data\n" * 100
+
+        with open(mnt_name, "wb") as fh:
+            fh.write(data)
+        with open(mnt_name, "rb") as fh:
+            assert fh.read() == data
+        with open(src_name, "rb") as fh:
+            assert fh.read() == data
+
+        os.unlink(mnt_name)
+    except Exception:
+        cleanup(mount_process, mnt_dir)
+        raise
+    else:
+        umount(mount_process, mnt_dir)
+
+
+def test_bad_sftp_reply_len(tmpdir):
+    """sshfs must reject a zero-length SFTP reply instead of underflowing."""
+    helper = tmpdir.join("bad_sftp.py")
+    helper.write(
+        '#!/usr/bin/env python3\n'
+        'import os, struct, sys\n'
+        'def read_pkt():\n'
+        '    hdr = os.read(0, 4)\n'
+        '    if len(hdr) < 4: sys.exit(0)\n'
+        '    n = struct.unpack(">I", hdr)[0]\n'
+        '    while n:\n'
+        '        c = os.read(0, n)\n'
+        '        if not c: sys.exit(0)\n'
+        '        n -= len(c)\n'
+        'read_pkt()\n'
+        'os.write(1, struct.pack(">IBI", 5, 2, 3))\n'  # SSH_FXP_VERSION v3
+        'read_pkt()\n'
+        'os.write(1, struct.pack(">IB", 0, 0))\n'  # len=0 reply (5 bytes on wire)
+    )
+    helper.chmod(0o755)
+
+    mnt_dir = str(tmpdir.mkdir("mnt"))
+    cmdline = base_cmdline + [
+        pjoin(basename, "sshfs"),
+        "-f",
+        "dummy:/",
+        mnt_dir,
+        "-o", f"ssh_command={helper}",
+    ]
+    res = subprocess.run(
+        cmdline,
+        stdin=subprocess.DEVNULL,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+        timeout=10,
+        text=True,
+    )
+    assert res.returncode != 0
+    assert "bad reply len: 0" in res.stderr