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From: Gao Xiang <xiang@kernel.org>
To: Qingyu Zhang <usupergate@gmail.com>
Cc: Gao Xiang <xiang@kernel.org>, Chao Yu <chao@kernel.org>,
	linux-erofs@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Nikhil Gurudasani <nikhilgurudasani314@gmail.com>
Subject: Re: [BUG] erofs: LZMA stream state NULL deref after failed dict grow
Date: Wed, 2 Sep 2026 10:20:10 +0800	[thread overview]
Message-ID: <apeH2iPSptCvno8K@192.168.5.22> (raw)
In-Reply-To: <CAPBHda=tMkmjY3-WE-d8jnNfDt5bEsAvu1BCiwOT4FgqqYASEQ@mail.gmail.com>

Hi,

On Wed, Sep 02, 2026 at 10:04:41AM +0800, Qingyu Zhang wrote:
> Hello,
> 
> z_erofs_load_lzma_config() can leave strm->state == NULL while still
> publishing z_erofs_lzma_max_dictsize. The next mount of the same
> image skips realloc and decompress NULL-derefs.
> 
> Type: null-pointer dereference
> 
> * Summary
> 
>        for (strm = head; strm; strm = strm->next) {
>                if (strm->state)
>                        xz_dec_microlzma_end(strm->state);
>                strm->state = xz_dec_microlzma_alloc(..., dict_size);
>                if (!strm->state)
>                        err = -ENOMEM;
>        }
>        ...
>        z_erofs_lzma_max_dictsize = dict_size;  /* even if err */
> 
> On alloc failure the old state is already gone. The next mount sees
> max_dictsize >= dict_size and returns 0 without retrying. Then:
> 
>        xz_dec_microlzma_reset(strm->state, ...);  /* state is NULL */
> 

Actually there were similar reports:
https://sashiko.dev/#/patchset/20260714114729.3760594-1-michael.bommarito%40gmail.com
https://lore.kernel.org/r/20260830104109.60639-1-nikhilgurudasani314@gmail.com

I will reply Nikhil's patch soon.

Thanks,
Gao Xiang

      reply	other threads:[~2026-09-02  2:20 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-09-02  2:04 Qingyu Zhang
2026-09-02  2:20 ` Gao Xiang [this message]

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