From: Shile Zhang shile.zhang@linux.alibaba.com

[ Upstream commit cf84807f6dd0be5214378e66460cfc9187f532f9 ]

To fix following divide-by-zero error found by Syzkaller:

divide error: 0000 [#1] SMP PTI CPU: 7 PID: 8447 Comm: test Kdump: loaded Not tainted 4.19.24-8.al7.x86_64 #1 Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS rel-1.12.0-0-ga698c8995f-prebuilt.qemu.org 04/01/2014 RIP: 0010:fb_var_to_videomode+0xae/0xc0 Code: 04 44 03 46 78 03 4e 7c 44 03 46 68 03 4e 70 89 ce d1 ee 69 c0 e8 03 00 00 f6 c2 01 0f 45 ce 83 e2 02 8d 34 09 0f 45 ce 31 d2 <41> f7 f0 31 d2 f7 f1 89 47 08 f3 c3 66 0f 1f 44 00 00 0f 1f 44 00 RSP: 0018:ffffb7e189347bf0 EFLAGS: 00010246 RAX: 00000000e1692410 RBX: ffffb7e189347d60 RCX: 0000000000000000 RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffb7e189347c10 RBP: ffff99972a091c00 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000100 R13: 0000000000010000 R14: 00007ffd66baf6d0 R15: 0000000000000000 FS: 00007f2054d11740(0000) GS:ffff99972fbc0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f205481fd20 CR3: 00000004288a0001 CR4: 00000000001606a0 Call Trace: fb_set_var+0x257/0x390 ? lookup_fast+0xbb/0x2b0 ? fb_open+0xc0/0x140 ? chrdev_open+0xa6/0x1a0 do_fb_ioctl+0x445/0x5a0 do_vfs_ioctl+0x92/0x5f0 ? __alloc_fd+0x3d/0x160 ksys_ioctl+0x60/0x90 __x64_sys_ioctl+0x16/0x20 do_syscall_64+0x5b/0x190 entry_SYSCALL_64_after_hwframe+0x44/0xa9 RIP: 0033:0x7f20548258d7 Code: 44 00 00 48 8b 05 b9 15 2d 00 64 c7 00 26 00 00 00 48 c7 c0 ff ff ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 b8 10 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 8b 0d 89 15 2d 00 f7 d8 64 89 01 48

It can be triggered easily with following test code:

#include <linux/fb.h> #include <fcntl.h> #include <sys/ioctl.h> int main(void) { struct fb_var_screeninfo var = {.activate = 0x100, .pixclock = 60}; int fd = open("/dev/fb0", O_RDWR); if (fd < 0) return 1;

if (ioctl(fd, FBIOPUT_VSCREENINFO, &var)) return 1;

return 0; }

Signed-off-by: Shile Zhang shile.zhang@linux.alibaba.com Cc: Fredrik Noring noring@nocrew.org Cc: Daniel Vetter daniel.vetter@ffwll.ch Reviewed-by: Mukesh Ojha mojha@codeaurora.org Signed-off-by: Bartlomiej Zolnierkiewicz b.zolnierkie@samsung.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/video/fbdev/core/modedb.c | 3 +++ 1 file changed, 3 insertions(+)

diff --git a/drivers/video/fbdev/core/modedb.c b/drivers/video/fbdev/core/modedb.c index de119f11b78f9..455a15f701720 100644 --- a/drivers/video/fbdev/core/modedb.c +++ b/drivers/video/fbdev/core/modedb.c @@ -933,6 +933,9 @@ void fb_var_to_videomode(struct fb_videomode *mode, if (var->vmode & FB_VMODE_DOUBLE) vtotal *= 2;

+ if (!htotal || !vtotal) + return; + hfreq = pixclock/htotal; mode->refresh = hfreq/vtotal; }