diff mbox series

fbdev: fix divide error in fb_var_to_videomode

Message ID 1552998003-237288-1-git-send-email-shile.zhang@linux.alibaba.com (mailing list archive)
State New, archived
Headers show
Series fbdev: fix divide error in fb_var_to_videomode | expand

Commit Message

Shile Zhang March 19, 2019, 12:20 p.m. UTC 
From: Shile Zhang <shile.zhang@linux.alibaba.com>

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>
---
 drivers/video/fbdev/core/modedb.c | 3 +++
 1 file changed, 3 insertions(+)

Comments

Shile Zhang March 26, 2019, 5:54 a.m. UTC | #1 
Hi, Bartlomiej, Fredrik, Daniel,

Could you please help to have a look at this patch?

Many thanks!

-Shile

On 2019/3/19 20:20, shile.zhang@linux.alibaba.com wrote:
> From: Shile Zhang <shile.zhang@linux.alibaba.com>
>
> 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>
> ---
>   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 283d9307..ac04987 100644
> --- a/drivers/video/fbdev/core/modedb.c
> +++ b/drivers/video/fbdev/core/modedb.c
> @@ -935,6 +935,9 @@ 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;
>   }
Fredrik Noring March 29, 2019, 6:49 p.m. UTC | #2 
Hi Shile,

Thank you for your report and patch.

On Tue, Mar 26, 2019 at 01:54:13PM +0800, Shile Zhang wrote:
> Hi, Bartlomiej, Fredrik, Daniel,
> 
> Could you please help to have a look at this patch?

I have tested your patch with a MIPS R5900 system and indeed there is
a division by zero, although my kernel inhibits the exception that you
observed.

The statements

	mode->refresh = 0;

	if (!var->pixclock)
		return;

a bit further up in fb_var_to_videomode seem to suggest that setting
mode->refresh to zero signals an invalid value. Your patch makes sense
to me in that having htotal or vtotal zero is equally absurd.

The note above the function could be improved to clarify the meaning
of assigning zero to mode->refresh. The refresh field is marked as
optional in the fb_videomode structure definition; perhaps zero is a
special value for this purpose.

Interestingly, the division by zero on the MIPS R5900 assigns -1 to
mode->refresh, which isn't zero as one might prefer for a video mode
that is invalid. Your patch would correct this anomaly.

Hopefully Bartlomiej or someone else with authority to approve your
patch submission will have a look at it.

Fredrik

> On 2019/3/19 20:20, shile.zhang@linux.alibaba.com wrote:
> > From: Shile Zhang <shile.zhang@linux.alibaba.com>
> >
> > 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>
> > ---
> >   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 283d9307..ac04987 100644
> > --- a/drivers/video/fbdev/core/modedb.c
> > +++ b/drivers/video/fbdev/core/modedb.c
> > @@ -935,6 +935,9 @@ 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;
> >   }
Mukesh Ojha March 29, 2019, 8:46 p.m. UTC | #3 
On 3/19/2019 5:50 PM, shile.zhang@linux.alibaba.com wrote:
> From: Shile Zhang <shile.zhang@linux.alibaba.com>
>
> 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>

To avoid any exception we should include the check.
Looks fine to me.
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>

Cheers,
-Mukesh

> ---
>   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 283d9307..ac04987 100644
> --- a/drivers/video/fbdev/core/modedb.c
> +++ b/drivers/video/fbdev/core/modedb.c
> @@ -935,6 +935,9 @@ 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;
>   }
Bartlomiej Zolnierkiewicz April 1, 2019, 3:25 p.m. UTC | #4 
On 03/29/2019 09:46 PM, Mukesh Ojha wrote:
> 
> On 3/19/2019 5:50 PM, shile.zhang@linux.alibaba.com wrote:
>> From: Shile Zhang <shile.zhang@linux.alibaba.com>
>>
>> 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>
> 
> To avoid any exception we should include the check.
> Looks fine to me.
> Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>

Patch queued for v5.2, thanks.

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics
diff mbox series

Patch

diff --git a/drivers/video/fbdev/core/modedb.c b/drivers/video/fbdev/core/modedb.c
index 283d9307..ac04987 100644
--- a/drivers/video/fbdev/core/modedb.c
+++ b/drivers/video/fbdev/core/modedb.c
@@ -935,6 +935,9 @@  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;
 }