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

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@syzkaller.appspotmail.com
CC: stable@vger.kernel.org # 4.19+
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 5e3e13d..1be7cb2 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -921,16 +921,15 @@ static noinline struct btrfs_device *device_list_add(const char *path,
                /*
                 * We are going to replace the device path for a given devid,
                 * make sure it's the same device if the device is mounted
+                *
+                * NOTE: the device->fs_info may not be reliable here so pass
+                * in a NULL to message helpers instead. This avoids a possible
+                * use-after-free when the fs_info and fs_info->sb are already
+                * torn down.
                 */
                if (device->bdev) {
                        if (device->devt != path_devt) {
                                mutex_unlock(&fs_devices->device_list_mutex);
-                               /*
-                                * device->fs_info may not be reliable here, so
-                                * pass in a NULL instead. This avoids a
-                                * possible use-after-free when the fs_info and
-                                * fs_info->sb are already torn down.
-                                */
                                btrfs_warn_in_rcu(NULL,
        "duplicate device %s devid %llu generation %llu scanned by %s (%d)",
                                                  path, devid, found_transid,
@@ -938,7 +937,7 @@ 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,