[syzbot] [dri?] divide error in drm_mode_debug_printmodeline

[syzbot] [dri?] divide error in drm_mode_debug_printmodeline

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    ac347a0655db Merge tag 'arm64-fixes' of git://git.kernel.o..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=101ba588e80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=88e7ba51eecd9cd6
dashboard link: https://syzkaller.appspot.com/bug?extid=2e93e6fb36e6fdc56574
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=11252f97680000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10fd2498e80000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8fcb90d89768/disk-ac347a06.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/360d9341a71c/vmlinux-ac347a06.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a370aa406c63/bzImage-ac347a06.xz

The issue was bisected 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=1058223f680000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=1258223f680000
console output: https://syzkaller.appspot.com/x/log.txt?x=1458223f680000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")

divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
 drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
 drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b
RIP: 0033:0x7f6c63dd6729
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:00007ffcde0dd0e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffcde0dd2b8 RCX: 00007f6c63dd6729
RDX: 0000000020000180 RSI: 00000000c06864a2 RDI: 0000000000000003
RBP: 00007f6c63e49610 R08: 00000000fffff4e6 R09: 00007ffcde0dd2b8
R10: 0000000000000003 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffcde0dd2a8 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_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
FS:  0000555556932380(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000064392c CR3: 000000007fcff000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
----------------
Code disassembly (best guess):
   0:	00 41 0f             	add    %al,0xf(%rcx)
   3:	b7 07                	mov    $0x7,%bh
   5:	66 83 f8 02          	cmp    $0x2,%ax
   9:	b9 01 00 00 00       	mov    $0x1,%ecx
   e:	0f 43 c8             	cmovae %eax,%ecx
  11:	0f b7 c1             	movzwl %cx,%eax
  14:	0f af e8             	imul   %eax,%ebp
  17:	44 89 f0             	mov    %r14d,%eax
  1a:	48 69 c8 e8 03 00 00 	imul   $0x3e8,%rax,%rcx
  21:	89 e8                	mov    %ebp,%eax
  23:	d1 e8                	shr    %eax
  25:	48 01 c8             	add    %rcx,%rax
  28:	31 d2                	xor    %edx,%edx
* 2a:	48 f7 f5             	div    %rbp <-- trapping instruction
  2d:	49 89 c6             	mov    %rax,%r14
  30:	eb 0c                	jmp    0x3e
  32:	e8 fb 07 66 fc       	call   0xfc660832
  37:	eb 05                	jmp    0x3e
  39:	e8 f4 07 66 fc       	call   0xfc660832
  3e:	48                   	rex.W
  3f:	89                   	.byte 0x89


---
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Re: [syzbot] [PATCH] test divide error in drm_mode_debug_printmodeline

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Subject: [PATCH] test divide error in drm_mode_debug_printmodeline
Author: lizhi.xu@windriver.com

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
index c613f0abe9dc..19e37e92dfaf 100644
--- a/include/drm/drm_modes.h
+++ b/include/drm/drm_modes.h
@@ -422,7 +422,7 @@ struct drm_display_mode {
 /**
  * DRM_MODE_FMT - printf string for &struct drm_display_mode
  */
-#define DRM_MODE_FMT    "\"%s\": %d %d %d %d %d %d %d %d %d %d 0x%x 0x%x"
+#define DRM_MODE_FMT    "\"%s\": %llu %d %d %d %d %d %d %d %d %d 0x%x 0x%x"
 
 /**
  * DRM_MODE_ARG - printf arguments for &struct drm_display_mode
@@ -526,7 +526,7 @@ static inline int of_get_drm_panel_display_mode(struct device_node *np,
 #endif
 
 void drm_mode_set_name(struct drm_display_mode *mode);
-int drm_mode_vrefresh(const struct drm_display_mode *mode);
+long drm_mode_vrefresh(const struct drm_display_mode *mode);
 void drm_mode_get_hv_timing(const struct drm_display_mode *mode,
 			    int *hdisplay, int *vdisplay);
 
diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..6f376001728c 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1283,9 +1283,9 @@ EXPORT_SYMBOL(drm_mode_set_name);
  * @modes's vrefresh rate in Hz, rounded to the nearest integer. Calculates the
  * value first if it is not yet set.
  */
-int drm_mode_vrefresh(const struct drm_display_mode *mode)
+long drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned long num, den;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;

Re: [syzbot]

[syzbot]

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Subject: 
Author: mazinalhaddad05@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

Re: [syzbot]

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

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Subject: 
Author: mazinalhaddad05@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
master

Re: [syzbot] [PATCH] Test divide err in drm

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Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git 888cf78c29e2

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..e3f05539f704 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1283,9 +1283,9 @@ EXPORT_SYMBOL(drm_mode_set_name);
  * @modes's vrefresh rate in Hz, rounded to the nearest integer. Calculates the
  * value first if it is not yet set.
  */
-int drm_mode_vrefresh(const struct drm_display_mode *mode)
+long drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned long num, den;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1300,6 +1300,8 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode)
 	if (mode->vscan > 1)
 		den *= mode->vscan;
 
+	printk("mode: %p, ht: %llu, vt: %llu, c: %llu, vsc: %llu, den: %llu, num: %llu, %s", 
+		mode, mode->htotal, mode->vtotal, mode->clock, mode->vscan, den, num, __func__);
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);
diff --git a/include/drm/drm_modes.h b/include/drm/drm_modes.h
index c613f0abe9dc..19e37e92dfaf 100644
--- a/include/drm/drm_modes.h
+++ b/include/drm/drm_modes.h
@@ -422,7 +422,7 @@ struct drm_display_mode {
 /**
  * DRM_MODE_FMT - printf string for &struct drm_display_mode
  */
-#define DRM_MODE_FMT    "\"%s\": %d %d %d %d %d %d %d %d %d %d 0x%x 0x%x"
+#define DRM_MODE_FMT    "\"%s\": %llu %d %d %d %d %d %d %d %d %d 0x%x 0x%x"
 
 /**
  * DRM_MODE_ARG - printf arguments for &struct drm_display_mode
@@ -526,7 +526,7 @@ static inline int of_get_drm_panel_display_mode(struct device_node *np,
 #endif
 
 void drm_mode_set_name(struct drm_display_mode *mode);
-int drm_mode_vrefresh(const struct drm_display_mode *mode);
+long drm_mode_vrefresh(const struct drm_display_mode *mode);
 void drm_mode_get_hv_timing(const struct drm_display_mode *mode,
 			    int *hdisplay, int *vdisplay);
 

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

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Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..0b0dd1c7b217 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1285,7 +1285,7 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, n1k;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,9 +1297,14 @@ 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) {
+		n1k = mul_u32_u32(num, 1000);
+		if (den < n1k)
+			den *= mode->vscan;
+	}
 
+	printk("mode: %p, ht: %d, vt: %d, c: %d, vsc: %d, den: %ld, num: %ld, n1k: %ld, %s", 
+		mode, mode->htotal, mode->vtotal, mode->clock, mode->vscan, den, num, n1k, __func__);
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..ca481c7f23e1 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1285,7 +1285,8 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, n1k;
+	int ret;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,9 +1298,15 @@ 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) {
+		n1k = mul_u32_u32(num, 1000);
+		if (den < n1k)
+			den *= mode->vscan;
+	}
+	ret = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 
+	printk("mode: %p, ht: %d, vt: %d, c: %d, vsc: %d, den: %ld, num: %ld, n1k: %ld, %d, %s", 
+		mode, mode->htotal, mode->vtotal, mode->clock, mode->vscan, den, num, n1k, ret, __func__);
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..539aa26cfc72 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1285,7 +1285,8 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, n1k;
+	int ret;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,9 +1298,17 @@ 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;
+	n1k = mul_u32_u32(num, 1000);
+	if (mode->vscan > 1) {
+		if (den < n1k)
+			den *= mode->vscan;
+	}
+	if (den < n1k)
+		den = n1k + 1;
+	ret = DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 
+	printk("mode: %p, ht: %d, vt: %d, c: %d, vsc: %d, den: %ld, num: %ld, n1k: %ld, %d, %s", 
+		mode, mode->htotal, mode->vtotal, mode->clock, mode->vscan, den, num, n1k, ret, __func__);
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
 EXPORT_SYMBOL(drm_mode_vrefresh);

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..1a3e8f3c1ece 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/log2.h>
 
 #include <video/of_display_timing.h>
 #include <video/of_videomode.h>
@@ -1297,8 +1298,12 @@ 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)
+	if (mode->vscan > 1) {
+		printk("%d, %d, %s\n", ilog2(den), ilog2(mode->vscan), __func__);
+		if (ilog2(den) + ilog2(mode->vscan) >= 32)
+			return -EINVAL;
 		den *= mode->vscan;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }

[PATCH] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Edward Adam Davis]

[Syz Log]
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
 drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
 drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

[Analysis]
When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
there is a probability of unsigned integer overflow.

[Fix]
Before multiplying by vscan, first determine their ilog2. When their total 
exceeds 32, return -EINVAL and exit the subsequent calculation.

Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 drivers/gpu/drm/drm_modes.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..c7ec1ab041f8 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/log2.h>
 
 #include <video/of_display_timing.h>
 #include <video/of_videomode.h>
@@ -1297,8 +1298,11 @@ 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)
+	if (mode->vscan > 1) {
+		if (ilog2(den) + ilog2(mode->vscan) >= 32)
+			return -EINVAL;
 		den *= mode->vscan;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
-- 
2.25.1

Re: [PATCH] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Jani Nikula]

On Sun, 19 Nov 2023, Edward Adam Davis <eadavis@qq.com> wrote:
> [Syz Log]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> [Analysis]
> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
> there is a probability of unsigned integer overflow.
>
> [Fix]
> Before multiplying by vscan, first determine their ilog2. When their total 
> exceeds 32, return -EINVAL and exit the subsequent calculation.
>
> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index ac9a406250c5..c7ec1ab041f8 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/log2.h>
>  
>  #include <video/of_display_timing.h>
>  #include <video/of_videomode.h>
> @@ -1297,8 +1298,11 @@ 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)
> +	if (mode->vscan > 1) {
> +		if (ilog2(den) + ilog2(mode->vscan) >= 32)

For future reference, check_mul_overflow() is the way to handle this.

> +			return -EINVAL;

Just so there's no confusion: NAK.

I'd be surprised if there were even a single place in the kernel where
someone checks drm_mode_vrefresh() for a negative error return.

This function must succeed.

Please change the types as needed instead.


BR,
Jani.

>  		den *= mode->vscan;
> +	}
>  
>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>  }

-- 
Jani Nikula, Intel

Re: [PATCH] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Jani Nikula]

On Sun, 19 Nov 2023, Edward Adam Davis <eadavis@qq.com> wrote:
> [Syz Log]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>
> [Analysis]
> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
> there is a probability of unsigned integer overflow.
>
> [Fix]
> Before multiplying by vscan, first determine their ilog2. When their total 
> exceeds 32, return -EINVAL and exit the subsequent calculation.
>
> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index ac9a406250c5..c7ec1ab041f8 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/log2.h>
>  
>  #include <video/of_display_timing.h>
>  #include <video/of_videomode.h>
> @@ -1297,8 +1298,11 @@ 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)
> +	if (mode->vscan > 1) {
> +		if (ilog2(den) + ilog2(mode->vscan) >= 32)

For future reference, check_mul_overflow() is the way to handle this.

> +			return -EINVAL;

Just so there's no confusion: NAK.

I'd be surprised if there were even a single place in the kernel where
someone checks drm_mode_vrefresh() for a negative error return.

This function must succeed.

Please change the types as needed instead.


BR,
Jani.

>  		den *= mode->vscan;
> +	}
>  
>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>  }

-- 
Jani Nikula, Intel

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..117ee4e41c63 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 +1298,11 @@ 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)
+	if (mode->vscan > 1) {
+		if (unlikely(check_mul_overflow(den, mode->vscan, &den)))
+			return 0;
 		den *= mode->vscan;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index ac9a406250c5..7c6d0229630d 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>
@@ -1285,7 +1286,7 @@ EXPORT_SYMBOL(drm_mode_set_name);
  */
 int drm_mode_vrefresh(const struct drm_display_mode *mode)
 {
-	unsigned int num, den;
+	unsigned int num, den, x;
 
 	if (mode->htotal == 0 || mode->vtotal == 0)
 		return 0;
@@ -1297,8 +1298,11 @@ 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)
+	if (mode->vscan > 1) {
+		if (unlikely(check_mul_overflow(den, mode->vscan, &x)))
+			return 0;
 		den *= mode->vscan;
+	}
 
 	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }

Re: [syzbot] [PATCH] Test divide err in drm

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: [PATCH] Test divide err in drm
Author: eadavis@qq.com

please test divide err in drm

#syz test https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git ac347a0655db

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);
 }

[PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Edward Adam Davis]

[Syz Log]
divide error: 0000 [#1] PREEMPT SMP KASAN
CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
 drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
 drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x63/0x6b

[Analysis]
When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
there is a probability of unsigned integer overflow.

[Fix]
Before multiplying by vscan, first check if their product will overflow. 
If overflow occurs, return 0 and exit the subsequent process.

Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 drivers/gpu/drm/drm_modes.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletion(-)

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);
 }
-- 
2.25.1

Re: [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Ville Syrjälä]

On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
> [Syz Log]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> [Analysis]
> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
> there is a probability of unsigned integer overflow.
> 
> [Fix]
> Before multiplying by vscan, first check if their product will overflow. 
> If overflow occurs, return 0 and exit the subsequent process.
> 
> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletion(-)
> 
> 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;
> +	}

I can't see any driver that actually supports vscan>1. Only
nouveau has some code for it, but doesn't look like it does
anything sensible. All other drivers for sure should be
rejecting vscan>1 outright. Which driver is this?

Is there an actual usecase where nouveau needs this (and does
it even work?) or could we just rip out the whole thing and
reject vscan>1 globally?

>  
>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>  }
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel

Re: [Nouveau] [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Ville Syrjälä]

On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
> [Syz Log]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> [Analysis]
> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
> there is a probability of unsigned integer overflow.
> 
> [Fix]
> Before multiplying by vscan, first check if their product will overflow. 
> If overflow occurs, return 0 and exit the subsequent process.
> 
> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletion(-)
> 
> 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;
> +	}

I can't see any driver that actually supports vscan>1. Only
nouveau has some code for it, but doesn't look like it does
anything sensible. All other drivers for sure should be
rejecting vscan>1 outright. Which driver is this?

Is there an actual usecase where nouveau needs this (and does
it even work?) or could we just rip out the whole thing and
reject vscan>1 globally?

>  
>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>  }
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel

Re: [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Ville Syrjälä]

On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
> [Syz Log]
> divide error: 0000 [#1] PREEMPT SMP KASAN
> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>  <TASK>
>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
> 
> [Analysis]
> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
> there is a probability of unsigned integer overflow.
> 
> [Fix]
> Before multiplying by vscan, first check if their product will overflow. 
> If overflow occurs, return 0 and exit the subsequent process.
> 
> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletion(-)
> 
> 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;
> +	}

I can't see any driver that actually supports vscan>1. Only
nouveau has some code for it, but doesn't look like it does
anything sensible. All other drivers for sure should be
rejecting vscan>1 outright. Which driver is this?

Is there an actual usecase where nouveau needs this (and does
it even work?) or could we just rip out the whole thing and
reject vscan>1 globally?

>  
>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>  }
> -- 
> 2.25.1

-- 
Ville Syrjälä
Intel

Re: [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Jani Nikula]

On Mon, 20 Nov 2023, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
>> [Syz Log]
>> divide error: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
>> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
>> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
>> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
>> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
>> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
>> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
>> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
>> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
>> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
>> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  <TASK>
>>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>>  vfs_ioctl fs/ioctl.c:51 [inline]
>>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> 
>> [Analysis]
>> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
>> there is a probability of unsigned integer overflow.
>> 
>> [Fix]
>> Before multiplying by vscan, first check if their product will overflow. 
>> If overflow occurs, return 0 and exit the subsequent process.
>> 
>> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
>> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
>> ---
>>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletion(-)
>> 
>> 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;
>> +	}
>
> I can't see any driver that actually supports vscan>1. Only
> nouveau has some code for it, but doesn't look like it does
> anything sensible. All other drivers for sure should be
> rejecting vscan>1 outright. Which driver is this?
>
> Is there an actual usecase where nouveau needs this (and does
> it even work?) or could we just rip out the whole thing and
> reject vscan>1 globally?

I thought the whole thing seemed familiar [1].

BR,
Jani.



[1] https://lore.kernel.org/r/20230802174746.2256-1-astrajoan@yahoo.com


>
>>  
>>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>>  }
>> -- 
>> 2.25.1

-- 
Jani Nikula, Intel

Re: [Nouveau] [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Jani Nikula]

On Mon, 20 Nov 2023, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
>> [Syz Log]
>> divide error: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
>> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
>> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
>> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
>> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
>> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
>> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
>> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
>> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
>> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
>> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  <TASK>
>>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>>  vfs_ioctl fs/ioctl.c:51 [inline]
>>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> 
>> [Analysis]
>> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
>> there is a probability of unsigned integer overflow.
>> 
>> [Fix]
>> Before multiplying by vscan, first check if their product will overflow. 
>> If overflow occurs, return 0 and exit the subsequent process.
>> 
>> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
>> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
>> ---
>>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletion(-)
>> 
>> 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;
>> +	}
>
> I can't see any driver that actually supports vscan>1. Only
> nouveau has some code for it, but doesn't look like it does
> anything sensible. All other drivers for sure should be
> rejecting vscan>1 outright. Which driver is this?
>
> Is there an actual usecase where nouveau needs this (and does
> it even work?) or could we just rip out the whole thing and
> reject vscan>1 globally?

I thought the whole thing seemed familiar [1].

BR,
Jani.



[1] https://lore.kernel.org/r/20230802174746.2256-1-astrajoan@yahoo.com


>
>>  
>>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>>  }
>> -- 
>> 2.25.1

-- 
Jani Nikula, Intel

Re: [PATCH V2] drm/modes: Fix divide error in drm_mode_debug_printmodeline

[Jani Nikula]

On Mon, 20 Nov 2023, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
>> [Syz Log]
>> divide error: 0000 [#1] PREEMPT SMP KASAN
>> CPU: 0 PID: 5068 Comm: syz-executor357 Not tainted 6.6.0-syzkaller-16039-gac347a0655db #0
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/09/2023
>> RIP: 0010:drm_mode_vrefresh drivers/gpu/drm/drm_modes.c:1303 [inline]
>> RIP: 0010:drm_mode_debug_printmodeline+0x118/0x4e0 drivers/gpu/drm/drm_modes.c:60
>> Code: 00 41 0f b7 07 66 83 f8 02 b9 01 00 00 00 0f 43 c8 0f b7 c1 0f af e8 44 89 f0 48 69 c8 e8 03 00 00 89 e8 d1 e8 48 01 c8 31 d2 <48> f7 f5 49 89 c6 eb 0c e8 fb 07 66 fc eb 05 e8 f4 07 66 fc 48 89
>> RSP: 0018:ffffc9000391f8d0 EFLAGS: 00010246
>> RAX: 000000000001f400 RBX: ffff888025045000 RCX: 000000000001f400
>> RDX: 0000000000000000 RSI: 0000000000008000 RDI: ffff888025045018
>> RBP: 0000000000000000 R08: ffffffff8528b9af R09: 0000000000000000
>> R10: ffffc9000391f8a0 R11: fffff52000723f17 R12: 0000000000000080
>> R13: dffffc0000000000 R14: 0000000000000080 R15: ffff888025045016
>> FS:  0000555556932380(0000) GS:ffff8880b9800000(0000) knlGS:0000000000000000
>> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>> CR2: 00000000005fdeb8 CR3: 000000007fcff000 CR4: 00000000003506f0
>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
>> Call Trace:
>>  <TASK>
>>  drm_mode_setcrtc+0x83b/0x1880 drivers/gpu/drm/drm_crtc.c:794
>>  drm_ioctl_kernel+0x362/0x500 drivers/gpu/drm/drm_ioctl.c:792
>>  drm_ioctl+0x636/0xb00 drivers/gpu/drm/drm_ioctl.c:895
>>  vfs_ioctl fs/ioctl.c:51 [inline]
>>  __do_sys_ioctl fs/ioctl.c:871 [inline]
>>  __se_sys_ioctl+0xf8/0x170 fs/ioctl.c:857
>>  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
>>  do_syscall_64+0x44/0x110 arch/x86/entry/common.c:82
>>  entry_SYSCALL_64_after_hwframe+0x63/0x6b
>> 
>> [Analysis]
>> When calculating den in drm_mode_vrefresh(), if the vscan value is too large, 
>> there is a probability of unsigned integer overflow.
>> 
>> [Fix]
>> Before multiplying by vscan, first check if their product will overflow. 
>> If overflow occurs, return 0 and exit the subsequent process.
>> 
>> Reported-and-tested-by: syzbot+2e93e6fb36e6fdc56574@syzkaller.appspotmail.com
>> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
>> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
>> ---
>>  drivers/gpu/drm/drm_modes.c | 7 +++++--
>>  1 file changed, 5 insertions(+), 2 deletion(-)
>> 
>> 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;
>> +	}
>
> I can't see any driver that actually supports vscan>1. Only
> nouveau has some code for it, but doesn't look like it does
> anything sensible. All other drivers for sure should be
> rejecting vscan>1 outright. Which driver is this?
>
> Is there an actual usecase where nouveau needs this (and does
> it even work?) or could we just rip out the whole thing and
> reject vscan>1 globally?

I thought the whole thing seemed familiar [1].

BR,
Jani.



[1] https://lore.kernel.org/r/20230802174746.2256-1-astrajoan@yahoo.com


>
>>  
>>  	return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
>>  }
>> -- 
>> 2.25.1

-- 
Jani Nikula, Intel