lkml.org 
[lkml]   [2007]   [Jun]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2.6.21.3] ppp_mppe: account for osize too small errors in mppe_decompress()
Thanks for pointing this out. It seems that we would need to allocate
this extra byte somewhere in kernel ppp code.

However, I am not very familiar with that part of the code yet, and
I'll appreciate any help with finding parts of code where obuffer for
mppe_decompress is allocated.

On 6/20/07, Sergey Vlasov <vsu@altlinux.ru> wrote:
> On Tue, 05 Jun 2007 22:23:02 +1100 Konstantin Sharlaimov wrote:
>
> > Prevent mppe_decompress() from generating "osize too small" errors when checking
> > for output buffer size. When receiving a packet of mru size the output buffer
> > for decrypted data is 1 byte too small since mppe_decompress() tries to account
> > for possible PFC, however later in code it is assumed no PFC.
> >
> > Adjusting the check prevented there errors from occurring.
> >
> > Signed-off-by: Konstantin Sharlaimov <konstantin.sharlaimov@gmail.com>
> > ---
> > --- linux-2.6.21.3/drivers/net/ppp_mppe.c.orig 2007-06-01 20:57:04.000000000 +1100
> > +++ linux-2.6.21.3/drivers/net/ppp_mppe.c 2007-06-05 21:46:30.000000000 +1100
> > @@ -493,14 +493,14 @@ mppe_decompress(void *arg, unsigned char
> >
> > /*
> > * Make sure we have enough room to decrypt the packet.
> > - * Note that for our test we only subtract 1 byte whereas in
> > - * mppe_compress() we added 2 bytes (+MPPE_OVHD);
> > - * this is to account for possible PFC.
> > + * To account for possible PFC we should only subtract 1
> > + * byte whereas in mppe_compress() we added 2 bytes (+MPPE_OVHD);
> > + * However, we assume no PFC, thus subtracting 2 bytes.
> > */
> > - if (osize < isize - MPPE_OVHD - 1) {
> > + if (osize < isize - MPPE_OVHD - 2) {
> > printk(KERN_DEBUG "mppe_decompress[%d]: osize too small! "
> > "(have: %d need: %d)\n", state->unit,
> > - osize, isize - MPPE_OVHD - 1);
> > + osize, isize - MPPE_OVHD - 2);
> > return DECOMP_ERROR;
> > }
> > osize = isize - MPPE_OVHD - 2; /* assume no PFC */
>
> Seems that this patch is not correct - even though the comment above
> says "assume no PFC", the subsequent code actually supports PFC:
>
> /*
> * Do PFC decompression.
> * This would be nicer if we were given the actual sk_buff
> * instead of a char *.
> */
> if ((obuf[0] & 0x01) != 0) {
> obuf[1] = obuf[0];
> obuf[0] = 0;
> obuf++;
> osize++;
> }
>
> Therefore, depending on the packet contents, the decompressor may
> really need that extra byte in the output buffer, and changing the
> check may cause buffer overflows.
>
>
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-19 23:35    [W:0.029 / U:0.860 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site