[PATCH] do_xip_mapping_read: fix length calculation

[PATCH] do_xip_mapping_read: fix length calculation

[Martin Schwidefsky]

From: Martin Schwidefsky <schwidefsky@de.ibm.com>

The calculation of the value nr in do_xip_mapping_read is incorrect. If
the copy required more than one iteration in the do while loop the
copies variable will be non-zero. The maximum length that may be passed
to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied
but the check only compares against (nr > len).

This bug is the cause for the heap corruption Carsten has been chasing
for so long:

*** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 ***  
======= Backtrace: =========  
/lib64/libc.so.6[0x200000b9b44]  
/lib64/libc.so.6(cfree+0x8e)[0x200000bdade]  
/bin/bash(free_buffered_stream+0x32)[0x80050e4e]  
/bin/bash(close_buffered_stream+0x1c)[0x80050ea4]  
/bin/bash(unset_bash_input+0x2a)[0x8001c366]  
/bin/bash(make_child+0x1d4)[0x8004115c]  
/bin/bash[0x8002fc3c]  
/bin/bash(execute_command_internal+0x656)[0x8003048e]  
/bin/bash(execute_command+0x5e)[0x80031e1e]  
/bin/bash(execute_command_internal+0x79a)[0x800305d2]  
/bin/bash(execute_command+0x5e)[0x80031e1e]  
/bin/bash(reader_loop+0x270)[0x8001efe0]  
/bin/bash(main+0x1328)[0x8001e960]  
/lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8]  
/bin/bash(clearerr+0x5e)[0x8001c092]  

With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2
"ext2/xip: refuse to change xip flag during remount with busy inodes"
can be removed again.

Cc: Carsten Otte <cotte@de.ibm.com>
Cc: Nick Piggin <npiggin@suse.de>
Cc: Jared Hulbert <jaredeh@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
---

 mm/filemap_xip.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff -urpN linux-2.6/mm/filemap_xip.c linux-2.6-patched/mm/filemap_xip.c
--- linux-2.6/mm/filemap_xip.c	2009-03-24 00:12:14.000000000 +0100
+++ linux-2.6-patched/mm/filemap_xip.c	2009-03-31 15:25:53.000000000 +0200
@@ -89,8 +89,8 @@ do_xip_mapping_read(struct address_space
 			}
 		}
 		nr = nr - offset;
-		if (nr > len)
-			nr = len;
+		if (nr > len - copied)
+			nr = len - copied;
 
 		error = mapping->a_ops->get_xip_mem(mapping, index, 0,
 							&xip_mem, &xip_pfn);

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Re: [PATCH] do_xip_mapping_read: fix length calculation

[Andrew Morton]

On Tue, 31 Mar 2009 15:32:23 +0200
Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:

> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
> 
> The calculation of the value nr in do_xip_mapping_read is incorrect. If
> the copy required more than one iteration in the do while loop the
> copies variable will be non-zero. The maximum length that may be passed
> to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied
> but the check only compares against (nr > len).
> 
> This bug is the cause for the heap corruption Carsten has been chasing
> for so long:
> 
> *** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 ***  
> ======= Backtrace: =========  
> /lib64/libc.so.6[0x200000b9b44]  
> /lib64/libc.so.6(cfree+0x8e)[0x200000bdade]  
> /bin/bash(free_buffered_stream+0x32)[0x80050e4e]  
> /bin/bash(close_buffered_stream+0x1c)[0x80050ea4]  
> /bin/bash(unset_bash_input+0x2a)[0x8001c366]  
> /bin/bash(make_child+0x1d4)[0x8004115c]  
> /bin/bash[0x8002fc3c]  
> /bin/bash(execute_command_internal+0x656)[0x8003048e]  
> /bin/bash(execute_command+0x5e)[0x80031e1e]  
> /bin/bash(execute_command_internal+0x79a)[0x800305d2]  
> /bin/bash(execute_command+0x5e)[0x80031e1e]  
> /bin/bash(reader_loop+0x270)[0x8001efe0]  
> /bin/bash(main+0x1328)[0x8001e960]  
> /lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8]  
> /bin/bash(clearerr+0x5e)[0x8001c092]  

Please get into the habit of adding Cc: <stable@kernel.org> to the
changelogs?

I believe I personally am pretty good at picking up stable things, but
other patch-mergers are quite unreliable.  We all need as much help as
we can get on this, because things are falling through cracks.

> With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2
> "ext2/xip: refuse to change xip flag during remount with busy inodes"
> can be removed again.

OK, please send a standalone patch to do this at an appropriate time. 
I guess that this second patch won't be needed in -stable.

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Re: [PATCH] do_xip_mapping_read: fix length calculation

[Martin Schwidefsky]

On Wed, 1 Apr 2009 14:17:00 -0700
Andrew Morton <akpm@linux-foundation.org> wrote:

> On Tue, 31 Mar 2009 15:32:23 +0200
> Martin Schwidefsky <schwidefsky@de.ibm.com> wrote:
>
> Please get into the habit of adding Cc: <stable@kernel.org> to the
> changelogs?

Ok, I've made me a sticky note and attached it to my monitor. Perhaps
that will help me to remember .. 

> I believe I personally am pretty good at picking up stable things, but
> other patch-mergers are quite unreliable.  We all need as much help as
> we can get on this, because things are falling through cracks.

Ok, makes sense. Better safe than sorry.
 
> > With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2
> > "ext2/xip: refuse to change xip flag during remount with busy inodes"
> > can be removed again.
> 
> OK, please send a standalone patch to do this at an appropriate time. 
> I guess that this second patch won't be needed in -stable.
 
The revert should be done either with the bug fix or after the bug fix
hit mainline. Guess I just create the patch and send it.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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Re: [PATCH] do_xip_mapping_read: fix length calculation

[Jared Hulbert]

> This bug is the cause for the heap corruption Carsten has been chasing
> for so long:

Finally saw this issue on ARM.  Some programs in Android on ARM were
crashing with AXFS.  This fixed it.

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Re: [PATCH] do_xip_mapping_read: fix length calculation

[Minchan Kim]

Nice catch!

I tested this patch on ext2's ramdisk with xip.
It fixed following bug.

*** stack smashing detected ***: <unknown> terminated
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0xb7fe5138]
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x0)[0xb7fe50f0]
[0x80485f8]
[0x0]
======= Memory map: ========
08048000-08049000 r-xp 00000000 01:00 12         /mnt/xip_test
08049000-0804a000 rw-p 00000000 01:00 12         /mnt/xip_test
0804a000-0806b000 rw-p 0804a000 00:00 0          [heap]
b7ef7000-b7ef8000 rw-p b7ef7000 00:00 0
b7ef8000-b8041000 r-xp 00000000 08:03 4219915    /lib/tls/i686/cmov/libc-2.7.so
b8041000-b8042000 r--p 00149000 08:03 4219915    /lib/tls/i686/cmov/libc-2.7.so
b8042000-b8044000 rw-p 0014a000 08:03 4219915    /lib/tls/i686/cmov/libc-2.7.so
b8044000-b8047000 rw-p b8044000 00:00 0
b8047000-b8051000 r-xp 00000000 08:03 4202508    /lib/libgcc_s.so.1
b8051000-b8052000 rw-p 0000a000 08:03 4202508    /lib/libgcc_s.so.1
b8052000-b8055000 rw-p b8052000 00:00 0
b8055000-b8056000 r-xp b8055000 00:00 0          [vdso]
b8056000-b8070000 r-xp 00000000 08:03 4202565    /lib/ld-2.7.so
b8070000-b8072000 rw-p 00019000 08:03 4202565    /lib/ld-2.7.so
bf95c000-bf971000 rw-p bffeb000 00:00 0          [stack]
Aborted


Reviewed-by: Minchan kim <minchan.kim@gmail.com>
Tested-by: Minchan kim <minchan.kim@gmail.com>


On Tue, Mar 31, 2009 at 10:32 PM, Martin Schwidefsky
<schwidefsky@de.ibm.com> wrote:
> From: Martin Schwidefsky <schwidefsky@de.ibm.com>
>
> The calculation of the value nr in do_xip_mapping_read is incorrect. If
> the copy required more than one iteration in the do while loop the
> copies variable will be non-zero. The maximum length that may be passed
> to the call to copy_to_user(buf+copied, xip_mem+offset, nr) is len-copied
> but the check only compares against (nr > len).
>
> This bug is the cause for the heap corruption Carsten has been chasing
> for so long:
>
> *** glibc detected *** /bin/bash: free(): invalid next size (normal): 0x00000000800e39f0 ***
> ======= Backtrace: =========
> /lib64/libc.so.6[0x200000b9b44]
> /lib64/libc.so.6(cfree+0x8e)[0x200000bdade]
> /bin/bash(free_buffered_stream+0x32)[0x80050e4e]
> /bin/bash(close_buffered_stream+0x1c)[0x80050ea4]
> /bin/bash(unset_bash_input+0x2a)[0x8001c366]
> /bin/bash(make_child+0x1d4)[0x8004115c]
> /bin/bash[0x8002fc3c]
> /bin/bash(execute_command_internal+0x656)[0x8003048e]
> /bin/bash(execute_command+0x5e)[0x80031e1e]
> /bin/bash(execute_command_internal+0x79a)[0x800305d2]
> /bin/bash(execute_command+0x5e)[0x80031e1e]
> /bin/bash(reader_loop+0x270)[0x8001efe0]
> /bin/bash(main+0x1328)[0x8001e960]
> /lib64/libc.so.6(__libc_start_main+0x100)[0x200000592a8]
> /bin/bash(clearerr+0x5e)[0x8001c092]
>
> With this bug fix the commit 0e4a9b59282914fe057ab17027f55123964bc2e2
> "ext2/xip: refuse to change xip flag during remount with busy inodes"
> can be removed again.
>
> Cc: Carsten Otte <cotte@de.ibm.com>
> Cc: Nick Piggin <npiggin@suse.de>
> Cc: Jared Hulbert <jaredeh@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> ---
>
>  mm/filemap_xip.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff -urpN linux-2.6/mm/filemap_xip.c linux-2.6-patched/mm/filemap_xip.c
> --- linux-2.6/mm/filemap_xip.c  2009-03-24 00:12:14.000000000 +0100
> +++ linux-2.6-patched/mm/filemap_xip.c  2009-03-31 15:25:53.000000000 +0200
> @@ -89,8 +89,8 @@ do_xip_mapping_read(struct address_space
>                        }
>                }
>                nr = nr - offset;
> -               if (nr > len)
> -                       nr = len;
> +               if (nr > len - copied)
> +                       nr = len - copied;
>
>                error = mapping->a_ops->get_xip_mem(mapping, index, 0,
>                                                        &xip_mem, &xip_pfn);
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
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>



-- 
Kinds regards,
Minchan Kim

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