Commit 734dabfb authored by Qu Wenruo's avatar Qu Wenruo Committed by Greg Kroah-Hartman
Browse files

btrfs: fix NULL pointer dereference when deleting device by invalid id

commit e4571b8c upstream.

It's easy to trigger NULL pointer dereference, just by removing a
non-existing device id:

 # mkfs.btrfs -f -m single -d single /dev/test/scratch1 \
 # mount /dev/test/scratch1 /mnt/btrfs
 # btrfs device remove 3 /mnt/btrfs

Then we have the following kernel NULL pointer dereference:

 BUG: kernel NULL pointer dereference, address: 0000000000000000
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 9 PID: 649 Comm: btrfs Not tainted 5.14.0-rc3-custom+ #35
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
 RIP: 0010:btrfs_rm_device+0x4de/0x6b0 [btrfs]
  btrfs_ioctl+0x18bb/0x3190 [btrfs]
  ? lock_is_held_type+0xa5/0x120
  ? find_held_lock.constprop.0+0x2b/0x80
  ? do_user_addr_fault+0x201/0x6a0
  ? lock_release+0xd2/0x2d0
  ? __x64_sys_ioctl+0x83/0xb0

Commit a27a94c2 ("btrfs: Make btrfs_find_device_by_devspec return
btrfs_device directly") moves the "missing" device path check into

But btrfs_rm_device() itself can have case where it only receives
@devid, with NULL as @device_path.

In that case, calling strcmp() on NULL will trigger the NULL pointer

Before that commit, we handle the "missing" case inside
btrfs_find_device_by_devspec(), which will not check @device_path at all
if @devid is provided, thus no way to trigger the bug.

Before calling strcmp(), also make sure @device_path is not NULL.

Fixes: a27a94c2

 ("btrfs: Make btrfs_find_device_by_devspec return btrfs_device directly")
CC: # 5.4+
Reported-by: default avatarbutt3rflyh4ck <>
Reviewed-by: default avatarAnand Jain <>
Signed-off-by: default avatarQu Wenruo <>
Reviewed-by: default avatarDavid Sterba <>
Signed-off-by: default avatarDavid Sterba <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 8bde7b30
......@@ -2137,7 +2137,7 @@ int btrfs_rm_device(struct btrfs_fs_info *fs_info, const char *device_path,
if (IS_ERR(device)) {
if (PTR_ERR(device) == -ENOENT &&
strcmp(device_path, "missing") == 0)
device_path && strcmp(device_path, "missing") == 0)
ret = PTR_ERR(device);
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