On Mon, Dec 05, 2022 at 02:35:39AM -0800, syzbot wrote: > syzbot has found a reproducer for the following issue on: > > HEAD commit: 0ba09b173387 Revert "mm: align larger anonymous mappings o.. > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=15550c47880000 > kernel config: https://syzkaller.appspot.com/x/.config?x=2325e409a9a893e1 > dashboard link: https://syzkaller.appspot.com/bug?extid=912776840162c13db1a3 > compiler: Debian clang version 13.0.1-++20220126092033+75e33f71c2da-1~exp1~20220126212112.63, GNU ld (GNU Binutils for Debian) 2.35.2 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=128c9e23880000 > > Downloadable assets: > disk image: https://storage.googleapis.com/syzbot-assets/9758ec2c06f4/disk-0ba09b17.raw.xz > vmlinux: https://storage.googleapis.com/syzbot-assets/06781dbfd581/vmlinux-0ba09b17.xz > kernel image: https://storage.googleapis.com/syzbot-assets/3d44a22d15fa/bzImage-0ba09b17.xz > mounted in repro: https://storage.googleapis.com/syzbot-assets/335889b2d730/mount_0.gz > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+912776840162c13db1a3@xxxxxxxxxxxxxxxxxxxxxxxxx #syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master xfs: dquot shrinker doesn't check for XFS_DQFLAG_FREEING From: Dave Chinner <dchinner@xxxxxxxxxx> Resulting in a UAF if the shrinker races with some other dquot freeing mechanism that sets XFS_DQFLAG_FREEING before the dquot is removed from the LRU. This can occur if a dquot purge races with drop_caches. Reported-by: syzbot+912776840162c13db1a3@xxxxxxxxxxxxxxxxxxxxxxxxx Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> --- fs/xfs/xfs_qm.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 18bb4ec4d7c9..ff53d40a2dae 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -422,6 +422,14 @@ xfs_qm_dquot_isolate( if (!xfs_dqlock_nowait(dqp)) goto out_miss_busy; + /* + * If something else is freeing this dquot and hasn't yet removed it + * from the LRU, leave it for the freeing task to complete the freeing + * process rather than risk it being free from under us here. + */ + if (dqp->q_flags & XFS_DQFLAG_FREEING) + goto out_miss_unlock; + /* * This dquot has acquired a reference in the meantime remove it from * the freelist and try again. @@ -441,10 +449,8 @@ xfs_qm_dquot_isolate( * skip it so there is time for the IO to complete before we try to * reclaim it again on the next LRU pass. */ - if (!xfs_dqflock_nowait(dqp)) { - xfs_dqunlock(dqp); - goto out_miss_busy; - } + if (!xfs_dqflock_nowait(dqp)) + goto out_miss_unlock; if (XFS_DQ_IS_DIRTY(dqp)) { struct xfs_buf *bp = NULL; @@ -478,6 +484,8 @@ xfs_qm_dquot_isolate( XFS_STATS_INC(dqp->q_mount, xs_qm_dqreclaims); return LRU_REMOVED; +out_miss_unlock: + xfs_dqunlock(dqp); out_miss_busy: trace_xfs_dqreclaim_busy(dqp); XFS_STATS_INC(dqp->q_mount, xs_qm_dqreclaim_misses);
