[PATCH] fs: xfs: fix possible NULL pointer dereference in xfs_buf_ioapply_map()

[Zixuan Fu]

In our fault-injection testing, bio_alloc() may fail with low memory and
return NULL. In this case, the variable "bio" in xfs_buf_ioapply_map()
would be NULL and then it is dereferenced by the next instruction
"bio->bi_iter.bi_sector".

The failure log is listed as follows:

[   11.929658] BUG: kernel NULL pointer dereference, address: 0000000000000015
...
[   11.932963] RIP: 0010:xfs_buf_ioapply_map+0x2cc/0x6f0 [xfs]
...
[   11.940043] Call Trace:
[   11.940247]  <TASK>
[   11.940416]  ? _raw_spin_unlock_irqrestore+0x3c/0x70
[   11.940827]  _xfs_buf_ioapply+0x134/0x4d0 [xfs]
[   11.941256]  __xfs_buf_submit+0x585/0x7a0 [xfs]
[   11.941684]  ? _xfs_buf_read+0xb7/0x120 [xfs]
[   11.942127]  _xfs_buf_read+0xb7/0x120 [xfs]
[   11.942535]  xfs_buf_read_map+0x1ba/0x650 [xfs]
[   11.942981]  ? xfs_read_agf+0x163/0x260 [xfs]
[   11.943394]  xfs_trans_read_buf_map+0x37c/0x850 [xfs]
[   11.943883]  ? xfs_read_agf+0x163/0x260 [xfs]
[   11.944306]  ? xfs_read_agf+0x163/0x260 [xfs]
[   11.944725]  xfs_read_agf+0x163/0x260 [xfs]
[   11.945141]  xfs_alloc_read_agf+0xc5/0x480 [xfs]
[   11.945574]  xfs_alloc_pagf_init+0x89/0x150 [xfs]
[   11.946037]  xfs_ag_resv_init+0x14b/0x5c0 [xfs]
[   11.946471]  xfs_fs_reserve_ag_blocks+0xf3/0x290 [xfs]
[   11.946961]  xfs_mountfs+0x2298/0x2440 [xfs]
[   11.947372]  xfs_fs_fill_super+0x1eaa/0x21e0 [xfs]
[   11.947840]  get_tree_bdev+0x3c3/0x5f0
[   11.948136]  ? xfs_fs_warn_deprecated+0x100/0x100 [xfs]
[   11.948633]  xfs_fs_get_tree+0x68/0xb0 [xfs]
[   11.949056]  vfs_get_tree+0x81/0x220
[   11.949336]  path_mount+0x1061/0x2340
[   11.949619]  ? kasan_quarantine_put+0x2c/0x1a0
[   11.949991]  ? slab_free_freelist_hook+0xde/0x160
[   11.950360]  ? mark_mounts_for_expiry+0x410/0x410
[   11.950729]  ? user_path_at_empty+0xf6/0x160
[   11.951072]  ? kmem_cache_free+0xb8/0x1a0
[   11.951384]  ? user_path_at_empty+0xf6/0x160
[   11.951717]  __se_sys_mount+0x217/0x2b0
[   11.952001]  ? __x64_sys_mount+0xd0/0xd0
[   11.952277]  ? exit_to_user_mode_prepare+0x32/0x130
[   11.952664]  do_syscall_64+0x41/0x90
[   11.952960]  entry_SYSCALL_64_after_hwframe+0x44/0xae
...
[   11.958483]  </TASK>

This patch adds a NULL check of "bio" and return immediately if it's NULL.

Reported-by: TOTE Robot <oslab@xxxxxxxxxxxxxxx>
Signed-off-by: Zixuan Fu <r33s3n6@xxxxxxxxx>
---
 fs/xfs/xfs_buf.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index e1afb9e503e1..1be98503b538 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -1447,6 +1447,9 @@ xfs_buf_ioapply_map(
 	nr_pages = bio_max_segs(total_nr_pages);
 
 	bio = bio_alloc(bp->b_target->bt_bdev, nr_pages, op, GFP_NOIO);
+	if (!bio)
+		return;
+
 	bio->bi_iter.bi_sector = sector;
 	bio->bi_end_io = xfs_buf_bio_end_io;
 	bio->bi_private = bp;
-- 
2.25.1