struct dm_ioctl has seven bytes of trailing padding, so the smallest buffer userspace is allowed to ask for, offsetof(struct dm_ioctl, data), is seven bytes shorter than sizeof(struct dm_ioctl).
get_result_buffer() sets data_start to sizeof(struct dm_ioctl) without looking at how big the buffer actually is. Ask for the minimum and data_start ends up seven bytes past the end. Callers add it to data_size, and ctl_ioctl() copies that much back to userspace: BUG: KASAN: slab-out-of-bounds in _copy_to_user+0xad/0xd0 Read of size 312 at addr ffff8880169e4c00 by task repro-dm/140 ctl_ioctl+0x5e3/0xcb0 dm_ctl_ioctl+0x25/0x40 allocated 305-byte region [ffff8880169e4c00, ffff8880169e4d31) A DM_LIST_DEVICES with data_size set to 305 is enough to hit it, and the seven bytes that leak are whatever sat next to the allocation. Clamp data_start to the buffer size. Reported-by: [email protected] Closes: https://syzkaller.appspot.com/bug?extid=48d935cf48a4a76be346 Fixes: 76c072b48e39 ("dm ioctl: move compat code") Cc: [email protected] Signed-off-by: Palla Raghunath <[email protected]> --- drivers/md/dm-ioctl.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c index a6b8e97755cd..211569dd3c54 100644 --- a/drivers/md/dm-ioctl.c +++ b/drivers/md/dm-ioctl.c @@ -656,6 +656,13 @@ static void *get_result_buffer(struct dm_ioctl *param, size_t param_size, { param->data_start = align_ptr(param + 1) - (void *) param; + /* + * The buffer can be as small as offsetof(*param, data), which is + * less than sizeof(*param), so don't run off the end of it. + */ + if (param->data_start > param_size) + param->data_start = param_size; + if (param->data_start < param_size) *len = param_size - param->data_start; else -- 2.34.1
