[PATCH] btrfs: don't access possibly stale fs_info data in device_list_add

[Dongliang Mu]

From: Dongliang Mu <mudongliangabcd@xxxxxxxxx>

Syzbot reported a possible use-after-free in printing information
in device_list_add.

Very similar with the bug fixed by commit 0697d9a61099 ("btrfs: don't
access possibly stale fs_info data for printing duplicate device"),
but this time the use occurs in btrfs_info_in_rcu.

============================================================
Call Trace:
 kasan_report.cold+0x83/0xdf mm/kasan/report.c:459
 btrfs_printk+0x395/0x425 fs/btrfs/super.c:244
 device_list_add.cold+0xd7/0x2ed fs/btrfs/volumes.c:957
 btrfs_scan_one_device+0x4c7/0x5c0 fs/btrfs/volumes.c:1387
 btrfs_control_ioctl+0x12a/0x2d0 fs/btrfs/super.c:2409
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:874 [inline]
 __se_sys_ioctl fs/ioctl.c:860 [inline]
 __x64_sys_ioctl+0x193/0x200 fs/ioctl.c:860
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x44/0xae
============================================================

Fix this by modifying device->fs_info to NULL too.

Reported-and-tested-by: syzbot+82650a4e0ed38f218363@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Dongliang Mu <mudongliangabcd@xxxxxxxxx>
---
 fs/btrfs/volumes.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index b07d382d53a8..c1325bdae9a1 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -954,7 +954,7 @@ static noinline struct btrfs_device *device_list_add(const char *path,
 						  task_pid_nr(current));
 				return ERR_PTR(-EEXIST);
 			}
-			btrfs_info_in_rcu(device->fs_info,
+			btrfs_info_in_rcu(NULL,
 	"devid %llu device path %s changed to %s scanned by %s (%d)",
 					  devid, rcu_str_deref(device->name),
 					  path, current->comm,
-- 
2.25.1