[PATCH] xfs: fix a UAF when inode item push

[Long Li <leo.lilong@huawei.com>]

KASAN reported a UAF bug while fault injection test:

  ==================================================================
  BUG: KASAN: use-after-free in xfs_inode_item_push+0x2db/0x2f0
  Read of size 8 at addr ffff888022f74788 by task xfsaild/sda/479

  CPU: 0 PID: 479 Comm: xfsaild/sda Not tainted 6.2.0-rc7-00003-ga8a43e2eb5f6 #89
  Call Trace:
   <TASK>
   dump_stack_lvl+0x51/0x6a
   print_report+0x171/0x4a6
   kasan_report+0xb7/0x130
   xfs_inode_item_push+0x2db/0x2f0
   xfsaild+0x729/0x1f70
   kthread+0x290/0x340
   ret_from_fork+0x1f/0x30
   </TASK>

  Allocated by task 494:
   kasan_save_stack+0x22/0x40
   kasan_set_track+0x25/0x30
   __kasan_slab_alloc+0x58/0x70
   kmem_cache_alloc+0x197/0x5d0
   xfs_inode_item_init+0x62/0x170
   xfs_trans_ijoin+0x15e/0x240
   xfs_init_new_inode+0x573/0x1820
   xfs_create+0x6a1/0x1020
   xfs_generic_create+0x544/0x5d0
   vfs_mkdir+0x5d0/0x980
   do_mkdirat+0x14e/0x220
   __x64_sys_mkdir+0x6a/0x80
   do_syscall_64+0x39/0x80
   entry_SYSCALL_64_after_hwframe+0x63/0xcd

  Freed by task 14:
   kasan_save_stack+0x22/0x40
   kasan_set_track+0x25/0x30
   kasan_save_free_info+0x2e/0x40
   __kasan_slab_free+0x114/0x1b0
   kmem_cache_free+0xee/0x4e0
   xfs_inode_free_callback+0x187/0x2a0
   rcu_do_batch+0x317/0xce0
   rcu_core+0x686/0xa90
   __do_softirq+0x1b6/0x626

  The buggy address belongs to the object at ffff888022f74758
   which belongs to the cache xfs_ili of size 200
  The buggy address is located 48 bytes inside of
   200-byte region [ffff888022f74758, ffff888022f74820)

  The buggy address belongs to the physical page:
  page:ffffea00008bdd00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x22f74
  head:ffffea00008bdd00 order:1 compound_mapcount:0 subpages_mapcount:0 compound_pincount:0
  flags: 0x1fffff80010200(slab|head|node=0|zone=1|lastcpupid=0x1fffff)
  raw: 001fffff80010200 ffff888010ed4040 ffffea00008b2510 ffffea00008bde10
  raw: 0000000000000000 00000000001a001a 00000001ffffffff 0000000000000000
  page dumped because: kasan: bad access detected

  Memory state around the buggy address:
   ffff888022f74680: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
   ffff888022f74700: fc fc fc fc fc fc fc fc fc fc fc fa fb fb fb fb
  >ffff888022f74780: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                        ^
   ffff888022f74800: fb fb fb fb fc fc fc fc fc fc fc fc fc fc fc fc
   ffff888022f74880: fc fc 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ==================================================================

When reclaim inodes, it will race with inode item push if log is shutdown.
Consider the following call graph, xfs_inode and xfs_inode_log_item may
be freed after release bp, threefore, the lip cannot be accessed after this.

  CPU0					CPU1
  xfs_inode_item_push			xfs_reclaim_inode
  -------------------			-----------------
  xfs_buf_trylock(bp)
  spin_unlock(&lip->li_ailp->ail_lock)
  xfs_buf_relse(bp)
  					xfs_buf_lock(bp)
  					spin_lock(&ailp->ail_lock)
  					spin_unlock(&ailp->ail_lock)
  					xfs_buf_relse(bp)
					__xfs_inode_free(ip)
  spin_lock(&lip->li_ailp->ail_lock)

Fixes: 90c60e164012 ("xfs: xfs_iflush() is no longer necessary")
Signed-off-by: Long Li <leo.lilong@huawei.com>
---
 fs/xfs/xfs_inode_item.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_inode_item.c b/fs/xfs/xfs_inode_item.c
index ca2941ab6cbc..52895e51fac5 100644
--- a/fs/xfs/xfs_inode_item.c
+++ b/fs/xfs/xfs_inode_item.c
@@ -545,6 +545,7 @@ 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;
 
@@ -567,7 +568,7 @@ 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
@@ -591,7 +592,7 @@ xfs_inode_item_push(
 		rval = XFS_ITEM_LOCKED;
 	}
 
-	spin_lock(&lip->li_ailp->ail_lock);
+	spin_lock(&ailp->ail_lock);
 	return rval;
 }
 
-- 
2.31.1