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[209.85.217.45]) by smtp.gmail.com with ESMTPSA id a1e0cc1a2514c-87eeae649c4sm810186241.8.2025.06.10.00.42.17 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 10 Jun 2025 00:42:17 -0700 (PDT) Received: by mail-vs1-f45.google.com with SMTP id ada2fe7eead31-4e7b20be1eeso61963137.3; Tue, 10 Jun 2025 00:42:17 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCUfMLhOXSSZKx80G1eRPCWzIc4d1UBvyYU0EtkWs+J1qEOM1N7yCx6aoPpsFM5J0qFHfEBcQhqotu/7Jg==@vger.kernel.org, AJvYcCWWQTJ1EjIDIyB/ZbfubugZ67Y8IlnJ2a2PDhmF0XWmFppe/alqKP2sdudH+t5t5Qm/nmbvYaoVdl6zlcvV@vger.kernel.org X-Received: by 2002:a05:6102:689b:b0:4e6:d995:94f9 with SMTP id ada2fe7eead31-4e7728f4656mr11525695137.12.1749541337050; Tue, 10 Jun 2025 00:42:17 -0700 (PDT) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20250607194959.2457473-1-alexguo1023@gmail.com> In-Reply-To: <20250607194959.2457473-1-alexguo1023@gmail.com> From: Geert Uytterhoeven Date: Tue, 10 Jun 2025 09:42:05 +0200 X-Gmail-Original-Message-ID: X-Gm-Features: AX0GCFsmjX0CF6UEjYJ9k9A05JUeI50EYyxt9NE7N8zAYiqfImbi0RyB1A0JuFw Message-ID: Subject: Re: [PATCH] fbdev: pm3fb: Fix potential divide by zero To: Alex Guo Cc: deller@gmx.de, linux-fbdev@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Hi Alex, On Sat, 7 Jun 2025 at 22:14, Alex Guo wrote: > variable var->pixclock can be set by user. In case it equals to > zero, divide by zero would occur in pm3fb_check_var. Similar > crashes have happened in other fbdev drivers. There is no check > and modification on var->pixclock along the call chain to > pm3fb_check_var. So we fix this by checking whether 'pixclock' > is zero. > > Similar commit: commit 16844e58704 ("video: fbdev: tridentfb: > Error out if 'pixclock' equals zero") > > Signed-off-by: Alex Guo Thanks for your patch, which is now commit 59d1fc7b3e1ae9d4 ("fbdev: pm3fb: fix potential divide by zero") in fbdev/for-next. > --- a/drivers/video/fbdev/pm3fb.c > +++ b/drivers/video/fbdev/pm3fb.c > @@ -998,6 +998,9 @@ static int pm3fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info) > return -EINVAL; > } > > + if (!var->pixclock) > + return -EINVAL; While this fixes the crash, this is correct behavior for an fbdev driver. When a value is invalid, it should be rounded up to a valid value instead, if possible. > + > if (PICOS2KHZ(var->pixclock) > PM3_MAX_PIXCLOCK) { > DPRINTK("pixclock too high (%ldKHz)\n", > PICOS2KHZ(var->pixclock)); Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds