[PATCH 4.19 305/421] dm btree remove: assign new_root only when removal succeeds

Greg Kroah-Hartman
2021-07-19T16:27:39Z

From: Hou Tao <houtao1@huawei.com>

commit b6e58b5466b2959f83034bead2e2e1395cca8aeb upstream.

remove_raw() in dm_btree_remove() may fail due to IO read error
(e.g. read the content of origin block fails during shadowing),
and the value of shadow_spine::root is uninitialized, but
the uninitialized value is still assign to new_root in the
end of dm_btree_remove().

For dm-thin, the value of pmd->details_root or pmd->root will become
an uninitialized value, so if trying to read details_info tree again
out-of-bound memory may occur as showed below:

general protection fault, probably for non-canonical address 0x3fdcb14c8d7520
CPU: 4 PID: 515 Comm: dmsetup Not tainted 5.13.0-rc6
Hardware name: QEMU Standard PC
RIP: 0010:metadata_ll_load_ie+0x14/0x30
Call Trace:
sm_metadata_count_is_more_than_one+0xb9/0xe0
dm_tm_shadow_block+0x52/0x1c0
shadow_step+0x59/0xf0
remove_raw+0xb2/0x170
dm_btree_remove+0xf4/0x1c0
dm_pool_delete_thin_device+0xc3/0x140
pool_message+0x218/0x2b0
target_message+0x251/0x290
ctl_ioctl+0x1c4/0x4d0
dm_ctl_ioctl+0xe/0x20
__x64_sys_ioctl+0x7b/0xb0
do_syscall_64+0x40/0xb0
entry_SYSCALL_64_after_hwframe+0x44/0xae

Fixing it by only assign new_root when removal succeeds

Signed-off-by: Hou Tao <houtao1@huawei.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/md/persistent-data/dm-btree-remove.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/persistent-data/dm-btree-remove.c
+++ b/drivers/md/persistent-data/dm-btree-remove.c
@@ -549,7 +549,8 @@ int dm_btree_remove(struct dm_btree_info
delete_at(n, index);
}

- *new_root = shadow_root(&spine);
+ if (!r)
+ *new_root = shadow_root(&spine);
exit_shadow_spine(&spine);

return r;