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([2409:40c0:48:969e:e221:9e2d:e416:1b41]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-2ea06ef6a7esm2734394a91.4.2024.11.15.05.12.30 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 Nov 2024 05:12:32 -0800 (PST) Message-ID: <333658df-a767-437f-9566-857e8ff5867f@gmail.com> Date: Fri, 15 Nov 2024 18:42:27 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] video: fbdev: metronomefb: Fix buffer overflow in load_waveform() To: Helge Deller Cc: linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20241112202825.17322-1-surajsonawane0215@gmail.com> <7de29a8c-3325-4654-8afd-81f3f9a8d113@gmx.de> Content-Language: en-US From: Suraj Sonawane In-Reply-To: <7de29a8c-3325-4654-8afd-81f3f9a8d113@gmx.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 14/11/24 20:13, Helge Deller wrote: > On 11/12/24 21:28, Suraj Sonawane wrote: >> Fix an error detected by the Smatch tool: >> >> drivers/video/fbdev/metronomefb.c:220 load_waveform() error: >> buffer overflow 'wfm_hdr->stuff2a' 2 <= 4 >> drivers/video/fbdev/metronomefb.c:220 load_waveform() error: >> buffer overflow 'wfm_hdr->stuff2a' 2 <= 4 >> >> The access to wfm_hdr->stuff2a in the loop can lead to a buffer >> overflow if stuff2a is not large enough. To fix this, a check was >> added to ensure that stuff2a has sufficient space before accessing >> it. This prevents the overflow and improves the safety of the code. >> >> Signed-off-by: Suraj Sonawane >> --- >>   drivers/video/fbdev/metronomefb.c | 6 ++++++ >>   1 file changed, 6 insertions(+) >> >> diff --git a/drivers/video/fbdev/metronomefb.c >> b/drivers/video/fbdev/metronomefb.c >> index 6f0942c6e..9da55cef2 100644 >> --- a/drivers/video/fbdev/metronomefb.c >> +++ b/drivers/video/fbdev/metronomefb.c >> @@ -210,6 +210,12 @@ static int load_waveform(u8 *mem, size_t size, >> int m, int t, >>       } >>       wfm_hdr->mc += 1; >>       wfm_hdr->trc += 1; >> + >> +    if (sizeof(wfm_hdr->stuff2a) < 5) { >> +        dev_err(dev, "Error: insufficient space in stuff2a\n"); >> +        return -EINVAL; >> +    } >> + >>       for (i = 0; i < 5; i++) { >>           if (*(wfm_hdr->stuff2a + i) != 0) { >>               dev_err(dev, "Error: unexpected value in padding\n"); > > That patch is completely wrong. > There is > /* the waveform structure that is coming from userspace firmware */ > struct waveform_hdr { >         .... >         u8 stuff2a[2]; >         u8 stuff2b[3]; > > So, I *believe* the for-next loop wants to walk acrosss stuff2a and > stuff2b, > which have 5 entries together. So, basically the original code isn't nice > but still correct. > Your "sizeof()" check will always be false and is the wrong patch. > > If at all, I think the stuff2a and stuff 2b arrays should be joined. > Something like >         u8 stuff2[5]; /* this is actually 2-entry stuff2a and 3-entry > stuff2b */ > But again, I don't know much about this driver. > > Helge Thank you for the brief feedback. I see your point regarding stuff2a and stuff2b. I’ll study this approach and revise the patch if I find it to be the correct solution. Best regards, Suraj Sonawane