From: Letu Ren fantasquex@gmail.com
stable inclusion from stable-v5.10.141 commit 8fc778ee2fb2853f7a3531fa7273349640d8e4e9 category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I685FC
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=...
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commit 19f953e7435644b81332dd632ba1b2d80b1e37af upstream.
In `do_fb_ioctl()` of fbmem.c, if cmd is FBIOPUT_VSCREENINFO, var will be copied from user, then go through `fb_set_var()` and `info->fbops->fb_check_var()` which could may be `pm2fb_check_var()`. Along the path, `var->pixclock` won't be modified. This function checks whether reciprocal of `var->pixclock` is too high. If `var->pixclock` is zero, there will be a divide by zero error. So, it is necessary to check whether denominator is zero to avoid crash. As this bug is found by Syzkaller, logs are listed below.
divide error in pm2fb_check_var Call Trace: <TASK> fb_set_var+0x367/0xeb0 drivers/video/fbdev/core/fbmem.c:1015 do_fb_ioctl+0x234/0x670 drivers/video/fbdev/core/fbmem.c:1110 fb_ioctl+0xdd/0x130 drivers/video/fbdev/core/fbmem.c:1189
Reported-by: Zheyu Ma zheyuma97@gmail.com Signed-off-by: Letu Ren fantasquex@gmail.com Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Jialin Zhang zhangjialin11@huawei.com Reviewed-by: Zheng Zengkai zhengzengkai@huawei.com --- drivers/video/fbdev/pm2fb.c | 5 +++++ 1 file changed, 5 insertions(+)
diff --git a/drivers/video/fbdev/pm2fb.c b/drivers/video/fbdev/pm2fb.c index 0642555289e0..c12d46e28359 100644 --- a/drivers/video/fbdev/pm2fb.c +++ b/drivers/video/fbdev/pm2fb.c @@ -616,6 +616,11 @@ static int pm2fb_check_var(struct fb_var_screeninfo *var, struct fb_info *info) return -EINVAL; }
+ if (!var->pixclock) { + DPRINTK("pixclock is zero\n"); + return -EINVAL; + } + if (PICOS2KHZ(var->pixclock) > PM2_MAX_PIXCLOCK) { DPRINTK("pixclock too high (%ldKHz)\n", PICOS2KHZ(var->pixclock));