[syzbot] [dri?] divide error in drm_mode_convert_to_umode

[syzbot] [dri?] divide error in drm_mode_convert_to_umode

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    445a555e0623 Add linux-next specific files for 20240209
git tree:       linux-next
console+strace: https://syzkaller.appspot.com/x/log.txt?x=175fa6ec180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=85aa3388229f9ea9
dashboard link: https://syzkaller.appspot.com/bug?extid=0d7a3627fb6a42cf0863
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d4bd48180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=106ae642180000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9188bb84c998/disk-445a555e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3ce0c98eabb2/vmlinux-445a555e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ab801b1c1d6d/bzImage-445a555e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0d7a3627fb6a42cf0863@syzkaller.appspotmail.com

divide error: 0000 [#1] PREEMPT SMP KASAN PTI
CPU: 0 PID: 5068 Comm: syz-executor201 Not tainted 6.8.0-rc3-next-20240209-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/25/2024
RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
RIP: 0010:drm_mode_convert_to_umode+0x36a/0xc30 drivers/gpu/drm/drm_modes.c:2594
Code: 0f b7 03 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 44 0f af f8 44 89 f0 48 69 c8 e8 03 00 00 44 89 f8 d1 e8 48 01 c8 31 d2 <49> f7 f7 48 89 c3 eb 1a e8 19 a2 47 fc eb 05 e8 12 a2 47 fc 48 8b
RSP: 0018:ffffc900034ff660 EFLAGS: 00010246
RAX: 0000000000001f40 RBX: ffff8880176d9016 RCX: 0000000000001f40
RDX: 0000000000000000 RSI: ffffc900034ff720 RDI: dffffc0000000000
RBP: 0000000000000200 R08: ffffffff854c389a R09: ffff8880176d900a
R10: dffffc0000000000 R11: ffffed100366d143 R12: 1ffff11002edb202
R13: ffff8880176d9000 R14: 0000000000000008 R15: 0000000000000000
FS:  0000555555c18380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 0000000011012000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 drm_atomic_set_mode_for_crtc+0x14a/0x4a0 drivers/gpu/drm/drm_atomic_uapi.c:82
 __drm_atomic_helper_set_config+0x255/0xf80 drivers/gpu/drm/drm_atomic.c:1679
 drm_atomic_helper_set_config+0x8b/0x150 drivers/gpu/drm/drm_atomic_helper.c:3263
 drm_mode_setcrtc+0xbae/0x17c0 drivers/gpu/drm/drm_crtc.c:886
 drm_ioctl_kernel+0x33a/0x440 drivers/gpu/drm/drm_ioctl.c:744
 drm_ioctl+0x63a/0xb10 drivers/gpu/drm/drm_ioctl.c:841
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:857
 do_syscall_64+0xfb/0x240
 entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7fd888e1b7e9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffd99378a68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffd99378c38 RCX: 00007fd888e1b7e9
RDX: 0000000020000400 RSI: 00000000c06864a2 RDI: 0000000000000003
RBP: 00007fd888e8e610 R08: 0000000000000005 R09: 00007ffd99378c38
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffd99378c28 R14: 0000000000000001 R15: 0000000000000001
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
RIP: 0010:drm_mode_convert_to_umode+0x36a/0xc30 drivers/gpu/drm/drm_modes.c:2594
Code: 0f b7 03 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 44 0f af f8 44 89 f0 48 69 c8 e8 03 00 00 44 89 f8 d1 e8 48 01 c8 31 d2 <49> f7 f7 48 89 c3 eb 1a e8 19 a2 47 fc eb 05 e8 12 a2 47 fc 48 8b
RSP: 0018:ffffc900034ff660 EFLAGS: 00010246
RAX: 0000000000001f40 RBX: ffff8880176d9016 RCX: 0000000000001f40
RDX: 0000000000000000 RSI: ffffc900034ff720 RDI: dffffc0000000000
RBP: 0000000000000200 R08: ffffffff854c389a R09: ffff8880176d900a
R10: dffffc0000000000 R11: ffffed100366d143 R12: 1ffff11002edb202
R13: ffff8880176d9000 R14: 0000000000000008 R15: 0000000000000000
FS:  0000555555c18380(0000) GS:ffff8880b9500000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd888e95270 CR3: 0000000011012000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	0f b7 03             	movzwl (%rbx),%eax
   3:	66 83 f8 02          	cmp    $0x2,%ax
   7:	b9 01 00 00 00       	mov    $0x1,%ecx
   c:	0f 43 c8             	cmovae %eax,%ecx
   f:	0f b7 c1             	movzwl %cx,%eax
  12:	44 0f af f8          	imul   %eax,%r15d
  16:	44 89 f0             	mov    %r14d,%eax
  19:	48 69 c8 e8 03 00 00 	imul   $0x3e8,%rax,%rcx
  20:	44 89 f8             	mov    %r15d,%eax
  23:	d1 e8                	shr    %eax
  25:	48 01 c8             	add    %rcx,%rax
  28:	31 d2                	xor    %edx,%edx
* 2a:	49 f7 f7             	div    %r15 <-- trapping instruction
  2d:	48 89 c3             	mov    %rax,%rbx
  30:	eb 1a                	jmp    0x4c
  32:	e8 19 a2 47 fc       	call   0xfc47a250
  37:	eb 05                	jmp    0x3e
  39:	e8 12 a2 47 fc       	call   0xfc47a250
  3e:	48                   	rex.W
  3f:	8b                   	.byte 0x8b


---
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Re: [syzbot] [dri?] divide error in drm_mode_convert_to_umode

[syzbot]

syzbot has bisected this issue to:

commit ea40d7857d5250e5400f38c69ef9e17321e9c4a2
Author: Daniel Vetter <daniel.vetter@ffwll.ch>
Date:   Fri Oct 9 23:21:56 2020 +0000

    drm/vkms: fbdev emulation support

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14426df4180000
start commit:   445a555e0623 Add linux-next specific files for 20240209
git tree:       linux-next
final oops:     https://syzkaller.appspot.com/x/report.txt?x=16426df4180000
console output: https://syzkaller.appspot.com/x/log.txt?x=12426df4180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=85aa3388229f9ea9
dashboard link: https://syzkaller.appspot.com/bug?extid=0d7a3627fb6a42cf0863
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=17d4bd48180000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=106ae642180000

Reported-by: syzbot+0d7a3627fb6a42cf0863@syzkaller.appspotmail.com
Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[PATCH] Test divide err in drm

[Edward Adam Davis]

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..60739d861da2 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -36,6 +36,7 @@
 #include <linux/list.h>
 #include <linux/list_sort.h>
 #include <linux/of.h>
+#include <linux/overflow.h>
 
 #include <video/of_display_timing.h>
 #include <video/of_videomode.h>
@@ -1297,8 +1298,10 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode)
 		num *= 2;
 	if (mode->flags & DRM_MODE_FLAG_DBLSCAN)
 		den *= 2;
-	if (mode->vscan > 1)
-		den *= mode->vscan;
+	if (mode->vscan > 1) {
+		if (unlikely(check_mul_overflow(den, mode->vscan, &den)))
+			return 0;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }

Re: [syzbot] [dri?] divide error in drm_mode_convert_to_umode

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-and-tested-by: syzbot+0d7a3627fb6a42cf0863@syzkaller.appspotmail.com

Tested on:

commit:         ae00c445 Add linux-next specific files for 20240212
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=154105ec180000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4eb3a27eddb32a14
dashboard link: https://syzkaller.appspot.com/bug?extid=0d7a3627fb6a42cf0863
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=160d0724180000

Note: testing is done by a robot and is best-effort only.