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Date: Wed, 4 Mar 2009 14:20:06 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Jiri Kosina <jkosina@suse.cz>
Cc: Samuel.CUELLA@supinfo.com, adaplas@gmail.com, linux-kernel@vger.kernel.org,
       trivial@kernel.org, linux-fbdev-devel@lists.sourceforge.net
Subject: Re: [PATCH 2.6.28 ] i810: kernel crash fix when  struct
 fb_var_screeninfo is supplied
Message-Id: <20090304142006.20ad72fe.akpm@linux-foundation.org>
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On Wed, 4 Mar 2009 11:09:21 +0100 (CET)
Jiri Kosina <jkosina@suse.cz> wrote:

> On Thu, 26 Feb 2009, CUELLA Samuel wrote:
> 
> > from: Samuel CUELLA <samuel.cuella@supinfo.com>
> > 
> > This patch prevents the kernel from being crashed by a divide-by-zero operation when supplied an incorrectly filled 'struct fb_var_screeninfo' from userland.
> > 
> > Previously i810_main.c:1005 (i810_check_params) was using the global 'yres' symbol previously defined at i810_main.c:145
> > as a module parameter value holder (i810_main.c:2174). If i810fb is compiled-in or if this param doesn't get a default value, 
> > this direct usage leads to a divide-by-zero at i810_main.c:1005 (i810_check_params). The patch simply replace the 'yres' global,
> > perhaps undefined symbol usage by a given parameter structure lookup.
> > 
> > This problem occurs with directfb, mplayer -vo fbdev, SDL library.
> > It was also reported ( but non solved ) at : http://mail.directfb.org/pipermail/directfb-dev/2008-March/004050.html
> > Sample code to reproduce :
> > /*Comile with gcc crashfb.c -o crashfb*/
> > #include <fcntl.h>
> > #include <linux/fb.h>
> > #include <stdio.h>
> > #include <sys/ioctl.h>
> > #include <sys/mman.h>
> > #include <sys/stat.h>
> > #include <string.h>
> > #include <stdlib.h>
> > 
> > 
> > #define FB "/dev/fb0"
> > 
> > int main(){
> >         int fd;
> >         int rv;
> >         struct fb_var_screeninfo vinfo;
> > 
> >         fd = open(FB,O_RDWR);
> >         if( fd ){
> >                 vinfo.xres = 800;
> >                 vinfo.yres = 600;
> >                 rv =ioctl(fd, FBIOPUT_VSCREENINFO, &vinfo);
> >         }
> >         return(rv);
> > }
> > Leads to this crash dump:
> > divide error: 0000 [#1]
> > last sysfs file: /sys/kernel/uevent_seqnum
> > Modules linked in:
> > 
> > Pid: 4058, comm: crashfb Not tainted (2.6.28 #4)
> > EIP: 0060:[<c02558c8>] EFLAGS: 00010202 CPU: 0
> > EIP is at i810fb_check_var+0x428/0x520
> > EAX: 00400000 EBX: ce9d5e44 ECX: 001209a0 EDX: 00000000
> > ESI: 00000020 EDI: 00000004 EBP: 00000000 ESP: ce9d5d0c
> >  DS: 007b ES: 007b FS: 0000 GS: 0033 SS: 0068
> > Process crashfb (pid: 4058, ti=ce9d4000 task=cf8af0e0 task.ti=ce9d4000)
> > Stack:
> >  c014f993 00000000 00000001 00000000 00000000 00400000 0000001a cf811000
> >  08048268 cf81123c 00000258 00000320 ffffffed cf811015 ce9d5e45 cf811000
> >  c0224821 ce9d5e44 ce9b09a0 00000000 00012000 00000000 c0111a89 00000001
> > Call Trace:
> >  [<c014f993>] handle_mm_fault+0x5c3/0x650
> >  [<c0224821>] fb_set_var+0x61/0x2d0
> >  [<c0111a89>] do_page_fault+0x3a9/0x8b0
> >  [<c016c935>] do_lookup+0x65/0x1a0
> >  [<c02257aa>] fb_ioctl+0x21a/0x3c0
> >  [<c014f577>] handle_mm_fault+0x1a7/0x650
> >  [<c0225590>] fb_ioctl+0x0/0x3c0
> >  [<c017077f>] vfs_ioctl+0x1f/0x70
> >  [<c017096c>] do_vfs_ioctl+0x5c/0x430
> >  [<c0111a89>] do_page_fault+0x3a9/0x8b0
> >  [<c0170d7d>] sys_ioctl+0x3d/0x70
> >  [<c0103af9>] sysenter_do_call+0x12/0x25
> > Code: c0 0f 44 d0 89 54 24 04 e8 b6 5a ec ff b8 ea ff ff ff 83 c4 30 5b 5e 5f 5d c3 8b 2d ac 0e 4a c0 31 d2 89 f7 8b 44 24 14 c1 ef 03 <f7> f5 31 d2 f7 f7 3b 03 89 c7 0f 83 3c fd ff ff 89 c2 89 f1 89
> > EIP: [<c02558c8>] i810fb_check_var+0x428/0x520 SS:ESP 0068:ce9d5d0c
> > ---[ end trace 1840767f449d222e ]---
> > 
> > Despite this dump says that EIP was in 'i810fb_check_var' the divide by zero truly occurs in 'i810_check_params' called by 'i810fb_check_var' (i810_main.c:1466).
> > 
> > Signed-off-by: Samuel CUELLA <samuel.cuella@supinfo.com>
> > ---
> > --- linux-2.6.28/drivers/video/i810/i810_main.c.orig    2009-02-26 15:23:03.000000000 +0100
> > +++ linux-2.6.28/drivers/video/i810/i810_main.c 2009-02-26 14:50:06.000000000 +0100
> > @@ -993,6 +993,8 @@ static int i810_check_params(struct fb_v
> >         struct i810fb_par *par = info->par;
> >         int line_length, vidmem, mode_valid = 0, retval = 0;
> >         u32 vyres = var->yres_virtual, vxres = var->xres_virtual;
> > +       u32 yres = info->var.yres;
> > +
> >         /*
> >          *  Memory limit
> >          */
> > 
> 
> This is not appropriate for trivial tree. CCing akpm and lkml.
> 

I don't have a copy of the original patch.

Please resend everything, with full changelog and a Signed-off-by: as
per Documentation/SubmittingPatches.  Please also cc
linux-fbdev-devel@lists.sourceforge.net.