xfs: save ailp before dropping the AIL lock in push callbacks

In xfs_inode_item_push() and xfs_qm_dquot_logitem_push(), the AIL lock
is dropped to perform buffer IO. Once the cluster buffer no longer
protects the log item from reclaim, the log item may be freed by
background reclaim or the dquot shrinker. The subsequent spin_lock()
call dereferences lip->li_ailp, which is a use-after-free.

Fix this by saving the ailp pointer in a local variable while the AIL
lock is held and the log item is guaranteed to be valid.

Reported-by: syzbot+652af2b3c5569c4ab63c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=652af2b3c5569c4ab63c
Fixes: 90c60e164012 ("xfs: xfs_iflush() is no longer necessary")
Cc: stable@vger.kernel.org # v5.9
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Yuto Ohnuki <ytohnuki@amazon.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>

diff --git a/fs/xfs/xfs_dquot_item.c b/fs/xfs/xfs_dquot_item.c
index 491e2a7053a398ae8f5ff1fde21b0b7bdfafe77e..65a0e69c3d083b117d6609621f23ad6dfaeec878 100644 (file)
--- a/fs/xfs/xfs_dquot_item.c
+++ b/fs/xfs/xfs_dquot_item.c
@@ -125,6 +125,7 @@ xfs_qm_dquot_logitem_push(
        struct xfs_dq_logitem   *qlip = DQUOT_ITEM(lip);
        struct xfs_dquot        *dqp = qlip->qli_dquot;
        struct xfs_buf          *bp;
+       struct xfs_ail          *ailp = lip->li_ailp;
        uint                    rval = XFS_ITEM_SUCCESS;
        int                     error;
 
@@ -153,7 +154,7 @@ xfs_qm_dquot_logitem_push(
                goto out_unlock;
        }
 
-       spin_unlock(&lip->li_ailp->ail_lock);
+       spin_unlock(&ailp->ail_lock);
 
        error = xfs_dquot_use_attached_buf(dqp, &bp);
        if (error == -EAGAIN) {
@@ -172,9 +173,13 @@ xfs_qm_dquot_logitem_push(
                        rval = XFS_ITEM_FLUSHING;
        }
        xfs_buf_relse(bp);
+       /*
+        * The buffer no longer protects the log item from reclaim, so
+        * do not reference lip after this point.
+        */
 
 out_relock_ail:
-       spin_lock(&lip->li_ailp->ail_lock);
+       spin_lock(&ailp->ail_lock);
 out_unlock:
        mutex_unlock(&dqp->q_qlock);
        return rval;

diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
index 8913036b8024bda1250e709663aa8902641a7914..4ae81eed0442c7ee1829e6c0a65c26521870ac47 100644 (file)
--- a/fs/xfs/xfs_inode_item.c
+++ b/fs/xfs/xfs_inode_item.c
@@ -746,6 +746,7 @@ xfs_inode_item_push(
        struct xfs_inode_log_item *iip = INODE_ITEM(lip);
        struct xfs_inode        *ip = iip->ili_inode;
        struct xfs_buf          *bp = lip->li_buf;
+       struct xfs_ail          *ailp = lip->li_ailp;
        uint                    rval = XFS_ITEM_SUCCESS;
        int                     error;
 
@@ -771,7 +772,7 @@ xfs_inode_item_push(
        if (!xfs_buf_trylock(bp))
                return XFS_ITEM_LOCKED;
 
-       spin_unlock(&lip->li_ailp->ail_lock);
+       spin_unlock(&ailp->ail_lock);
 
        /*
         * We need to hold a reference for flushing the cluster buffer as it may
@@ -795,7 +796,11 @@ xfs_inode_item_push(
                rval = XFS_ITEM_LOCKED;
        }
 
-       spin_lock(&lip->li_ailp->ail_lock);
+       /*
+        * The buffer no longer protects the log item from reclaim, so
+        * do not reference lip after this point.
+        */
+       spin_lock(&ailp->ail_lock);
        return rval;
 }