linux-stable.git/tools/testing/selftests/filesystems/fuse/fuse_acl_cache_test.c, branch master Linux kernel stable tree selftests/fuse: add ACL_DONT_CACHE regression test 2026-07-21T20:04:02+00:00 Amir Goldstein amir73il@gmail.com 2026-07-13T22:09:32+00:00 9acb102522b92f24fba6b238b3668a4d9dfcb592 Add a test that reproduces the stale ACL bug fixed by: "fs: preserve ACL_DONT_CACHE state in forget_cached_acl()" A FUSE mount that does not negotiate FUSE_POSIX_ACL initialises inodes with i_acl = ACL_DONT_CACHE. Before the fix, calling forget_all_cached_acls() (e.g. from fuse_update_get_attr() on a statx(AT_STATX_FORCE_SYNC)) would silently replace ACL_DONT_CACHE with ACL_NOT_CACHED, enabling the kernel ACL cache. A subsequent getxattr would populate the cache, and because fuse_set_acl() skips forget_all_cached_acls() for !fc->posix_acl, later ACL changes were not visible to callers — getxattr returned stale data. The test mounts a minimal libfuse3 lowlevel filesystem (no FUSE_POSIX_ACL negotiated) and: 1. Issues two getxattrs — both must reach the daemon, proving ACL_DONT_CACHE suppresses caching before any trigger. 2. Calls statx(AT_STATX_FORCE_SYNC) to trigger forget_all_cached_acls(). 3. Issues another getxattr (populates the cache on a buggy kernel). 4. Switches the daemon to a different-sized ACL (ACL_B). 5. Issues a final getxattr — expects ACL_B (44 bytes) and daemon call count 4; a buggy kernel returns stale ACL_A (28 bytes). fuse_acl_cache_test is only built when libfuse3 is detected via pkg-config. Christian Brauner <brauner@kernel.org> says: Changed do_force_statx() to call the statx() libc wrapper instead of syscall(SYS_statx, ...) as requested by Amir after review feedback from Luis Henriques, and dropped the now unused <sys/syscall.h> include. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Link: https://patch.msgid.link/20260713220932.413004-3-amir73il@gmail.com Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> 
Add a test that reproduces the stale ACL bug fixed by:
  "fs: preserve ACL_DONT_CACHE state in forget_cached_acl()"

A FUSE mount that does not negotiate FUSE_POSIX_ACL initialises inodes
with i_acl = ACL_DONT_CACHE.  Before the fix, calling
forget_all_cached_acls() (e.g. from fuse_update_get_attr() on a
statx(AT_STATX_FORCE_SYNC)) would silently replace ACL_DONT_CACHE with
ACL_NOT_CACHED, enabling the kernel ACL cache.  A subsequent getxattr
would populate the cache, and because fuse_set_acl() skips
forget_all_cached_acls() for !fc->posix_acl, later ACL changes were
not visible to callers — getxattr returned stale data.

The test mounts a minimal libfuse3 lowlevel filesystem (no
FUSE_POSIX_ACL negotiated) and:
  1. Issues two getxattrs — both must reach the daemon, proving
     ACL_DONT_CACHE suppresses caching before any trigger.
  2. Calls statx(AT_STATX_FORCE_SYNC) to trigger forget_all_cached_acls().
  3. Issues another getxattr (populates the cache on a buggy kernel).
  4. Switches the daemon to a different-sized ACL (ACL_B).
  5. Issues a final getxattr — expects ACL_B (44 bytes) and daemon
     call count 4; a buggy kernel returns stale ACL_A (28 bytes).

fuse_acl_cache_test is only built when libfuse3 is detected via
pkg-config.

Christian Brauner <brauner@kernel.org> says:
Changed do_force_statx() to call the statx() libc wrapper instead of
syscall(SYS_statx, ...) as requested by Amir after review feedback from
Luis Henriques, and dropped the now unused <sys/syscall.h> include.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Link: https://patch.msgid.link/20260713220932.413004-3-amir73il@gmail.com
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>