On Tue, Dec 06, 2022 at 09:52:46AM +1100, Dave Chinner wrote: > 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 > > > > XFS (loop1): Quotacheck: Done. > > syz-executor.1 (4657): drop_caches: 2 > > ================================================================== > > BUG: KASAN: use-after-free in xfs_dquot_type fs/xfs/xfs_dquot.h:136 [inline] > > BUG: KASAN: use-after-free in xfs_qm_dqfree_one+0x12f/0x170 fs/xfs/xfs_qm.c:1604 > > Read of size 1 at addr ffff888079a6aa58 by task syz-executor.1/4657 > > Looks like we've missed a XFS_DQUOT_FREEING check in > xfs_qm_shrink_scan(), and the dquot purge run by unmount has raced > with the shrinker. Patch below should fix it. > > -Dave. > -- > Dave Chinner > david@xxxxxxxxxxxxx > > 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> Please repost this as a toplevel thread so it doesn't get lost in the depths. Anyway, this looks correct so: Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx> --D > --- > 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);
