Re: [PATCH 2.6.21.3] ppp_mppe: account for osize too small errors in mppe_decompress()
From: Sergey Vlasov <hidden>
Date: 2007-06-19 15:13:28
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On Tue, 05 Jun 2007 22:23:02 +1100 Konstantin Sharlaimov wrote:
quoted hunk
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 <redacted> ------ 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. Attachments
- (unnamed) [application/pgp-signature] 189 bytes