Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 20 Jun 2007 08:33:01 +1100 | From | Konstantin <> | Subject | Re: [PATCH 2.6.21.3] ppp_mppe: account for osize too small errors in mppe_decompress() |
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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/
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