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[82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4534172d2b0sm32503735e9.35.2025.06.15.01.30.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 15 Jun 2025 01:30:05 -0700 (PDT) Date: Sun, 15 Jun 2025 09:30:03 +0100 From: David Laight To: Alex Guo Cc: deller@gmx.de, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] fbdev: i740: Fix potential divide by zero Message-ID: <20250615093003.6e524fa9@pumpkin> In-Reply-To: <20250614051837.3544959-1-alexguo1023@gmail.com> References: <20250614051837.3544959-1-alexguo1023@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-fbdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 14 Jun 2025 01:18:37 -0400 Alex Guo wrote: > Variable var->pixclock can be set by user. In case it equals to > zero, divide by zero would occur in 4 switch branches in > i740fb_decode_var. > Similar crashes have happened in other fbdev drivers. We fix this > by checking whether 'pixclock' is zero. Doesn't it already hit the 'default' clause of the switch statement? David > > Similar commit: commit 16844e58704 ("video: fbdev: tridentfb: > Error out if 'pixclock' equals zero") > > Signed-off-by: Alex Guo > --- > drivers/video/fbdev/i740fb.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/drivers/video/fbdev/i740fb.c b/drivers/video/fbdev/i740fb.c > index 9b74dae71472..861e9e397b4e 100644 > --- a/drivers/video/fbdev/i740fb.c > +++ b/drivers/video/fbdev/i740fb.c > @@ -419,6 +419,10 @@ static int i740fb_decode_var(const struct fb_var_screeninfo *var, > > > bpp = var->bits_per_pixel; > + if (!var->pixclock){ > + dev_err(info->device, "pixclock must not be zero\n"); > + return -EINVAL; > + } > switch (bpp) { > case 1 ... 8: > bpp = 8;