linux-kernel - Re: [PATCH 3/3] dm-pcache: avoid leaking invalid metadata in pcache_meta_find

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Message-ID: <1248c78a-c471-496b-b7ac-892ac7335a08@linux.dev>
Date: Tue, 4 Nov 2025 14:46:33 +0800
From: Dongsheng Yang <dongsheng.yang@...ux.dev>
To: Li Chen <me@...ux.beauty>, Zheng Gu <cengku@...il.com>
Cc: dm-devel <dm-devel@...ts.linux.dev>,
 linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] dm-pcache: avoid leaking invalid metadata in
 pcache_meta_find_latest()


在 11/1/2025 9:10 PM, Li Chen 写道:
> Hi Zheng,
>
>   ---- On Fri, 31 Oct 2025 10:01:23 +0800  Zheng Gu <cengku@...il.com> wrote ---
>   >> On Thu, Oct 30, 2025 at 8:36 PM Li Chen <me@...ux.beauty> wrote:From: Li Chen <chenl311@...natelecom.cn>
>   >>
>   >> 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
>
>