With drop_privileges, mount.fuse3 execs the file system binary only
after dropping all capabilities (CAP_DAC_OVERRIDE included) while
keeping uid 0. The kernel then applies plain DAC checks to the exec, so
a binary under a directory the capability-less process cannot traverse
(e.g. a user-owned mode-0700 home) fails with EACCES and /bin/sh prints
a bare 'Permission denied', surfacing in the tests as 'file system
process terminated prematurely'.
Resolving and opening the binary before the drop was rejected: it would
perform a privileged path resolution and open() on invoker-influenced
input (confused-deputy / privilege-escalation risk). The drop-first,
resolve-after order is preserved.
Instead, pre-flight the upcoming PATH lookup after the drop and fail
with a diagnostic that names the binary and points at mount.fuse3(8).
The check runs with the final credentials, so it is deny-only. The test
detects the same situation up front (uid/gid-aware traversal check) and
skips with a precise reason; root-owned CI checkouts keep running.
Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
Teach mount.fuse3 how to start fuse via systemd service, if present.
Signed-off-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Bernd Schubert <bernd@bsbernd.com>
This addresses: https://github.com/libfuse/libfuse/issues/724
HAVE_LIBC_VERSIONED_SYMBOLS configures the library if to use
versioned symbols and is set at meson configuration time.
External filesystems (the main target, actually)
include fuse headers and the preprocessor
then acts on HAVE_LIBC_VERSIONED_SYMBOLS. Problem was now that
'config.h' was not distributed with libfuse and so
HAVE_LIBC_VERSIONED_SYMBOLS was never defined with external
tools and the preprocessor did the wrong decision.
This commit also increases the the minimal meson version,
as this depends on meson feature only available in 0.50
<quote 'meson' >
WARNING: Project specifies a minimum meson_
version '>= 0.42' but uses features which were added
in newer versions:
* 0.50.0: {'install arg in configure_file'}
</quote>
Additionally the config file has been renamed to "fuse_config.h"
to avoid clashes - 'config.h' is not very specific.
In mount.fuse.c, there are several memory leak problems in
main func. For example, setuid_name is allocated by calling
xstrdup func, however it is not freed before calling execl func.
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Haotian Li <lihaotian9@huawei.com>
In mount.fuse.c, pwd is set by calling getpwnam func.
If the matching entry is not found or an error occurs in
getpwnam func, pwd will be NULL. So we need to check
whether pwd is NULL before accessing it.
Signed-off-by: Zhiqiang Liu <liuzhiqiang26@huawei.com>
Signed-off-by: Haotian Li <lihaotian9@huawei.com>
IN a bunch of comments we say 'under the terms of the GNU GPL', make
it clear this is GPLv2 (as LICENSE says).
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
The unprivileged option allows to run the FUSE file system process
without privileges by dropping capabilities and preventing them from
being re-acquired via setuid / fscaps etc. To accomplish this,
mount.fuse sets up the `/dev/fuse` file descriptor and mount itself
and passes the file descriptor via the `/dev/fd/%u` mountpoint syntax
to the FUSE file system.
Bernd Schubert