[PATCH 3.16 024/245] btrfs: handle invalid num_stripes in sys_array

Ben Hutchings
2020-04-23T23:25:01Z

From: David Sterba <dsterba@suse.com>

commit f5cdedd73fa71b74dcc42f2a11a5735d89ce7c4f upstream.

We can handle the special case of num_stripes == 0 directly inside
btrfs_read_sys_array. The BUG_ON in btrfs_chunk_item_size is there to
catch other unhandled cases where we fail to validate external data.

A crafted or corrupted image crashes at mount time:

BTRFS: device fsid 9006933e-2a9a-44f0-917f-514252aeec2c devid 1 transid 7 /dev/loop0
BTRFS info (device loop0): disk space caching is enabled
BUG: failure at fs/btrfs/ctree.h:337/btrfs_chunk_item_size()!
Kernel panic - not syncing: BUG!
CPU: 0 PID: 313 Comm: mount Not tainted 4.2.5-00657-ge047887-dirty #25
Stack:
637af890 60062489 602aeb2e 604192ba
60387961 00000011 637af8a0 6038a835
637af9c0 6038776b 634ef32b 00000000
Call Trace:
[<6001c86d>] show_stack+0xfe/0x15b
[<6038a835>] dump_stack+0x2a/0x2c
[<6038776b>] panic+0x13e/0x2b3
[<6020f099>] btrfs_read_sys_array+0x25d/0x2ff
[<601cfbbe>] open_ctree+0x192d/0x27af
[<6019c2c1>] btrfs_mount+0x8f5/0xb9a
[<600bc9a7>] mount_fs+0x11/0xf3
[<600d5167>] vfs_kern_mount+0x75/0x11a
[<6019bcb0>] btrfs_mount+0x2e4/0xb9a
[<600bc9a7>] mount_fs+0x11/0xf3
[<600d5167>] vfs_kern_mount+0x75/0x11a
[<600d710b>] do_mount+0xa35/0xbc9
[<600d7557>] SyS_mount+0x95/0xc8
[<6001e884>] handle_syscall+0x6b/0x8e

Reported-by: Jiri Slaby <jslaby@suse.com>
Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
fs/btrfs/volumes.c | 8 ++++++++
1 file changed, 8 insertions(+)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -6092,6 +6092,14 @@ int btrfs_read_sys_array(struct btrfs_ro
goto out_short_read;

num_stripes = btrfs_chunk_num_stripes(sb, chunk);
+ if (!num_stripes) {
+ printk(KERN_ERR
+ "BTRFS: invalid number of stripes %u in sys_array at offset %u\n",
+ num_stripes, cur_offset);
+ ret = -EIO;
+ break;
+ }
+
len = btrfs_chunk_item_size(num_stripes);
if (cur_offset + len > array_size)
goto out_short_read;