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

2023-11-21 Thread Jani Nikula 
On Mon, 20 Nov 2023, Ville Syrjälä  wrote:
> On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
>> [Syz Log]
>> divide error:  [#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:c9000391f8d0 EFLAGS: 00010246
>> RAX: 0001f400 RBX: 888025045000 RCX: 0001f400
>> RDX:  RSI: 8000 RDI: 888025045018
>> RBP:  R08: 8528b9af R09: 
>> R10: c9000391f8a0 R11: f52000723f17 R12: 0080
>> R13: dc00 R14: 0080 R15: 888025045016
>> FS:  56932380() GS:8880b980() knlGS:
>> CS:  0010 DS:  ES:  CR0: 80050033
>> CR2: 005fdeb8 CR3: 7fcff000 CR4: 003506f0
>> DR0:  DR1:  DR2: 
>> DR3:  DR6: fffe0ff0 DR7: 0400
>> Call Trace:
>>  
>>  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+2e93e6fb36e6fdc56...@syzkaller.appspotmail.com
>> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
>> Signed-off-by: Edward Adam Davis 
>> ---
>>  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 
>>  #include 
>>  #include 
>> +#include 
>>  
>>  #include 
>>  #include 
>> @@ -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, )))
>> +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-astraj...@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

2023-11-20 Thread Ville Syrjälä 
On Mon, Nov 20, 2023 at 10:41:18PM +0800, Edward Adam Davis wrote:
> [Syz Log]
> divide error:  [#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:c9000391f8d0 EFLAGS: 00010246
> RAX: 0001f400 RBX: 888025045000 RCX: 0001f400
> RDX:  RSI: 8000 RDI: 888025045018
> RBP:  R08: 8528b9af R09: 
> R10: c9000391f8a0 R11: f52000723f17 R12: 0080
> R13: dc00 R14: 0080 R15: 888025045016
> FS:  56932380() GS:8880b980() knlGS:
> CS:  0010 DS:  ES:  CR0: 80050033
> CR2: 005fdeb8 CR3: 7fcff000 CR4: 003506f0
> DR0:  DR1:  DR2: 
> DR3:  DR6: fffe0ff0 DR7: 0400
> Call Trace:
>  
>  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+2e93e6fb36e6fdc56...@syzkaller.appspotmail.com
> Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
> Signed-off-by: Edward Adam Davis 
> ---
>  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 
>  #include 
>  #include 
> +#include 
>  
>  #include 
>  #include 
> @@ -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, )))
> + 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

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

2023-11-20 Thread Edward Adam Davis 
[Syz Log]
divide error:  [#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:c9000391f8d0 EFLAGS: 00010246
RAX: 0001f400 RBX: 888025045000 RCX: 0001f400
RDX:  RSI: 8000 RDI: 888025045018
RBP:  R08: 8528b9af R09: 
R10: c9000391f8a0 R11: f52000723f17 R12: 0080
R13: dc00 R14: 0080 R15: 888025045016
FS:  56932380() GS:8880b980() knlGS:
CS:  0010 DS:  ES:  CR0: 80050033
CR2: 005fdeb8 CR3: 7fcff000 CR4: 003506f0
DR0:  DR1:  DR2: 
DR3:  DR6: fffe0ff0 DR7: 0400
Call Trace:
 
 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+2e93e6fb36e6fdc56...@syzkaller.appspotmail.com
Fixes: ea40d7857d52 ("drm/vkms: fbdev emulation support")
Signed-off-by: Edward Adam Davis 
---
 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 
 #include 
 #include 
+#include 
 
 #include 
 #include 
@@ -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, )))
+   return 0;
+   }
 
return DIV_ROUND_CLOSEST_ULL(mul_u32_u32(num, 1000), den);
 }
-- 
2.25.1