在 11/1/2025 9:10 PM, Li Chen 写道:
Hi Zheng,
---- On Fri, 31 Oct 2025 10:01:23 +0800 Zheng Gu <[email protected]> wrote ---
>> On Thu, Oct 30, 2025 at 8:36 PM Li Chen <[email protected]> wrote:From: Li Chen
<[email protected]>
>>
>> Before this change pcache_meta_find_latest() was copying each
>> slot directly into meta_ret while scanning. If no valid slot
>> was found and the function returned NULL, meta_ret still held
>> whatever was last copied (possibly CRC-bad). Later users
>> (e.g. cache_segs_init) could mistakenly trust that data.
>
> This functions is * __must_check*, users must check the return value first
before touching the meta_ret, so it should not be a problem here.
Right now, the callers only check the return value with IS_ERR(). If the
function returns NULL instead of an error pointer, a caller like
cache_info_init() will assume that no valid cache_info was found because all
cache_info are
corrupted. Instead, it will try to init a new one, and then return 0 (success),
https://github.com/torvalds/linux/blob/master/drivers/md/dm-pcache/cache.c#L61
Later, cache_tail_init() will access cache->cache_info.flags. But in this
path all cache_info may have already been corrupted, and the CRCs are mismatched
(https://github.com/torvalds/linux/blob/ba36dd5ee6fd4643ebbf6ee6eefcecf0b07e35c7/drivers/md/dm-pcache/pcache_internal.h#L97),
so flags may contain garbage.
This commit fixes this issue by allocating a temp buffer with kvmalloc, so
meta_ret would never
contain corrupted values.
Hi
Thanx for your fix. So the better change should be reseting
cache_info in cache_info_init_default() firstly by memset() with 0.
Allocating a temp buffer in pcache_meta_find_latest() is really not a
good idea.
Thanx
Regards,
Li
