From 4b9a5458d02e214ef2b384124ca626e3e381d778 Mon Sep 17 00:00:00 2001 From: Amir Goldstein Date: Tue, 14 Jul 2026 00:09:31 +0200 Subject: [PATCH] fs: preserve ACL_DONT_CACHE state in forget_cached_acl() The ACL_DONT_CACHE state is meant to be a constant state for the inode for filesystems that want to opt out of posix acl caching. Commit facd61053cff1 ("fuse: fixes after adapting to new posix acl api") used this facility to opt out of posix acl caching for fuse inodes with fuse server that does not negotiate FUSE_POSIX_ACL (fc->posix_acl). The commit also takes care to gate the forget_all_cached_acls() call in fuse_set_acl() on fc->posix_acl because there is no need for it, but there are other placed in fuse code which call forget_all_cached_acls() unconditional to fc->posix_acl and those cause the loss of the ACL_DONT_CACHE state. This is not only a functional bug. Properly timed, a get_acl() from this fuse filesystem can return a stale cached value, as was observed in tests, because set_acl() does not invalidate the unintentional acl cache. We could fix this in fuse, but it actually makes no sense for the vfs helper forget_cached_acl() to invalidate the ACL_DONT_CACHE state, so let it not do that to fix fuse and future users of ACL_DONT_CACHE. Fixes: facd61053cff1 ("fuse: fixes after adapting to new posix acl api") Cc: stable@vger.kernel.org Signed-off-by: Amir Goldstein Link: https://patch.msgid.link/20260713220932.413004-2-amir73il@gmail.com Reviewed-by: Luis Henriques Signed-off-by: Christian Brauner (Amutable) --- fs/posix_acl.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/fs/posix_acl.c b/fs/posix_acl.c index b4bfe4ddf64e..3dc62c1c2708 100644 --- a/fs/posix_acl.c +++ b/fs/posix_acl.c @@ -93,6 +93,13 @@ static void __forget_cached_acl(struct posix_acl **p) { struct posix_acl *old; + /* + * ACL_DONT_CACHE is expected to be a "const" value and xchg it with + * ACL_NOT_CACHED would enable acl caching for the inode - + * clearly not what the caller has intended. + */ + if (READ_ONCE(*p) == ACL_DONT_CACHE) + return; old = xchg(p, ACL_NOT_CACHED); if (!is_uncached_acl(old)) posix_acl_release(old);