| From cf84807f6dd0be5214378e66460cfc9187f532f9 Mon Sep 17 00:00:00 2001 |
| From: Shile Zhang <shile.zhang@linux.alibaba.com> |
| Date: Mon, 1 Apr 2019 17:47:00 +0200 |
| Subject: fbdev: fix divide error in fb_var_to_videomode |
| |
| From: Shile Zhang <shile.zhang@linux.alibaba.com> |
| |
| commit cf84807f6dd0be5214378e66460cfc9187f532f9 upstream. |
| |
| 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: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| drivers/video/fbdev/core/modedb.c | 3 +++ |
| 1 file changed, 3 insertions(+) |
| |
| --- 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_video |
| if (var->vmode & FB_VMODE_DOUBLE) |
| vtotal *= 2; |
| |
| + if (!htotal || !vtotal) |
| + return; |
| + |
| hfreq = pixclock/htotal; |
| mode->refresh = hfreq/vtotal; |
| } |