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

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Message-ID: <19a4ecf1149.3c8a574d835968.4993900419375442453@linux.beauty>
Date: Tue, 04 Nov 2025 20:19:44 +0800
From: Li Chen <me@...ux.beauty>
To: "Jonathan Cameron" <jonathan.cameron@...wei.com>
Cc: "dm-devel" <dm-devel@...ts.linux.dev>,
	"linux-kernel" <linux-kernel@...r.kernel.org>,
	"Dongsheng Yang" <dongsheng.yang@...ux.dev>,
	"Zheng Gu" <cengku@...il.com>
Subject: Re: [PATCH 3/3] dm-pcache: avoid leaking invalid metadata in
 pcache_meta_find_latest()

Hi Jonathan,

 ---- On Mon, 03 Nov 2025 19:38:03 +0800  Jonathan Cameron <jonathan.cameron@...wei.com> wrote --- 
 > On Thu, 30 Oct 2025 20:33:21 +0800
 > 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.
 > > 
 > > Allocate a temporary buffer instead and only populate meta_ret after a
 > > valid/latest header is found. If no valid header exists we return NULL
 > > without touching meta_ret.
 > > 
 > > Also add __free(kvfree) so the temporary buffer is always freed, and
 > > include the needed headers.
 > > 
 > > Signed-off-by: Li Chen <chenl311@...natelecom.cn>
 > > ---
 > >  drivers/md/dm-pcache/pcache_internal.h | 13 +++++++++----
 > >  1 file changed, 9 insertions(+), 4 deletions(-)
 > > 
 > > diff --git a/drivers/md/dm-pcache/pcache_internal.h b/drivers/md/dm-pcache/pcache_internal.h
 > > index b7a3319d2bd3e..ac28f9dd2986f 100644
 > > --- a/drivers/md/dm-pcache/pcache_internal.h
 > > +++ b/drivers/md/dm-pcache/pcache_internal.h
 > > @@ -4,6 +4,8 @@
 > >  
 > >  #include <linux/delay.h>
 > >  #include <linux/crc32c.h>
 > > +#include <linux/slab.h>
 > > +#include <linux/cleanup.h>
 > >  
 > >  #define pcache_err(fmt, ...)                            \
 > >      pr_err("dm-pcache: %s:%u " fmt, __func__, __LINE__, ##__VA_ARGS__)
 > > @@ -79,14 +81,17 @@ static inline void __must_check *pcache_meta_find_latest(struct pcache_meta_head
 > >                      u32 meta_size, u32 meta_max_size,
 > >                      void *meta_ret)
 > >  {
 > > -    struct pcache_meta_header *meta, *latest = NULL;
 > > +    struct pcache_meta_header *latest = NULL;
 > > +    struct pcache_meta_header *meta __free(kvfree);
 > >      u32 i, seq_latest = 0;
 > > -    void *meta_addr;
 > >  
 > > -    meta = meta_ret;
 > > +    meta = kvzalloc(meta_size, GFP_KERNEL);
 > See the guidance notes in cleanup.h  THis hsould be
 > 
 >     struct pcache_meta_header *meta __free(kvfree) =
 >         kvzalloc(meta_size, GFP_KERNEL);
 > 
 > That is the constructor and destructor must be together. Inline variable
 > declarations are fine for this one type of use.

I appreciate your suggestion very much.

Regards,

Li