z_erofs_decompress_kickoff() can race with filesystem unmount, causing
a use-after-free on sbi->sync_decompress.
When I/O completes, z_erofs_endio() calls z_erofs_decompress_kickoff()
to queue z_erofs_decompressqueue_work() asynchronously. Then, after all
folios are unlocked, unmount workflow can proceed and sbi will be freed
before accessing to sbi->sync_decompress.
Thread (unmount) I/O completion kworker
queue_work
z_erofs_decompressqueue_work
(all folios are unlocked)
cleanup_mnt
..
erofs_kill_sb
erofs_sb_free
kfree(sbi)
access sbi->sync_decompress // UAF!!
Fixes: 40452ffca3c1 ("erofs: add sysfs node to control sync decompression
strategy")
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=52bae5c495dbe261a0bc
Signed-off-by: Gao Xiang <[email protected]>
---
fs/erofs/zdata.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 27ab7bd844ec..c6240dccbb0f 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -1455,6 +1455,9 @@ static void z_erofs_decompress_kickoff(struct
z_erofs_decompressqueue *io,
if (atomic_add_return(bios, &io->pending_bios))
return;
if (z_erofs_in_atomic()) {
+ /* See `sync_decompress` in sysfs-fs-erofs for more details */
+ if (sbi->sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
+ sbi->sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
#ifdef CONFIG_EROFS_FS_PCPU_KTHREAD
struct kthread_worker *worker;
@@ -1471,9 +1474,6 @@ static void z_erofs_decompress_kickoff(struct
z_erofs_decompressqueue *io,
#else
queue_work(z_erofs_workqueue, &io->u.work);
#endif
- /* See `sync_decompress` in sysfs-fs-erofs for more details */
- if (sbi->sync_decompress == EROFS_SYNC_DECOMPRESS_AUTO)
- sbi->sync_decompress = EROFS_SYNC_DECOMPRESS_FORCE_ON;
return;
}
gfp_flag = memalloc_noio_save();
--
2.43.5
