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Mon, 25 May 2026 16:00:06 -0700 (PDT) Received: from 474444807712 named unknown by gmailapi.google.com with HTTPREST; Mon, 25 May 2026 19:00:06 -0400 Received: from 474444807712 named unknown by gmailapi.google.com with HTTPREST; Mon, 25 May 2026 19:00:06 -0400 From: Farhad Alemi X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Mon, 25 May 2026 19:00:06 -0400 X-Gm-Features: AVHnY4JdodnWHanJq4oEats-3fz5fnvjcuA7KvA67IPIqSk_dHToD7Y7DBkCAtU Message-ID: Subject: [PATCH] omfs: fix UAF and broken empty-check in omfs_dir_is_empty() To: Bob Copeland Cc: linux-karma-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" omfs_dir_is_empty() releases the buffer head and then dereferences a pointer that lives inside its b_data: brelse(bh); return *ptr !=3D ~0; Once the buffer is released the underlying page may be reclaimed, so the post-brelse read is a slab-use-after-free. KASAN reports: BUG: KASAN: use-after-free in omfs_dir_is_empty fs/omfs/dir.c:235 Read of size 8 at addr ffff8881... The same statement is also semantically inverted. The loop above breaks when a non-`~0` (occupied) bucket is found, so on the break-out path the original `*ptr !=3D ~0` would read as 1 whenever the freed page still held its prior contents (the common case immediately after brelse); combined with the caller in omfs_remove(): if (S_ISDIR(inode->i_mode) && !omfs_dir_is_empty(inode)) return -ENOTEMPTY; this means rmdir(2) silently succeeded on non-empty OMFS directories, leaving their children as orphan inodes. On the loop-completion path (no non-`~0` bucket found), ptr was advanced one element past the bucket array, so the original return was also a latent out-of-bounds read. The loop's exit condition `i =3D=3D nbuckets` is precisely "no occupied bucket was found", i.e. "the directory is empty". Returning that instead of dereferencing `*ptr` removes the UAF, removes the latent OOB on the empty-directory path, and corrects the function's semantics to match its name and the caller contract. Reported-by: Farhad Alemi Signed-off-by: Farhad Alemi --- fs/omfs/dir.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/omfs/dir.c b/fs/omfs/dir.c index 2ed541fccf33..c6ba390aabd3 100644 --- a/fs/omfs/dir.c +++ b/fs/omfs/dir.c @@ -232,7 +232,7 @@ static int omfs_dir_is_empty(struct inode *inode) break; brelse(bh); - return *ptr !=3D ~0; + return i =3D=3D nbuckets; } static int omfs_remove(struct inode *dir, struct dentry *dentry) -- 2.43.0