From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jiri Bohac Subject: Re: [PATCH v2] ROSE: prevent heap corruption with bad facilities Date: Thu, 31 Mar 2011 20:02:25 +0200 Message-ID: <20110331180225.GA6677@midget.suse.cz> References: <1300603423.1869.18.camel@dan> <1300639685.26693.286.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dan Rosenberg , ralf@linux-mips.org, davem@davemloft.net, netdev@vger.kernel.org, security@kernel.org To: Ben Hutchings Return-path: Received: from cantor.suse.de ([195.135.220.2]:58256 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758792Ab1CaSC2 (ORCPT ); Thu, 31 Mar 2011 14:02:28 -0400 Content-Disposition: inline In-Reply-To: <1300639685.26693.286.camel@localhost> Sender: netdev-owner@vger.kernel.org List-ID: On Sun, Mar 20, 2011 at 04:48:05PM +0000, Ben Hutchings wrote: > @@ -365,49 +393,44 @@ static int rose_parse_ccitt(unsigned char *p, struct rose_facilities_struct *fac > return n; > } > > -int rose_parse_facilities(unsigned char *p, > +int rose_parse_facilities(unsigned char *p, unsigned packet_len, > struct rose_facilities_struct *facilities) > { > int facilities_len, len; > > facilities_len = *p++; > > - if (facilities_len == 0) > + if (facilities_len == 0 || (unsigned)facilities_len > packet_len) > return 0; > > - while (facilities_len > 0) { > - if (*p == 0x00) { > - facilities_len--; > - p++; > - > - switch (*p) { > - case FAC_NATIONAL: /* National */ > - len = rose_parse_national(p + 1, facilities, facilities_len - 1); > - if (len < 0) > - return 0; > - facilities_len -= len + 1; > - p += len + 1; > - break; > - > - case FAC_CCITT: /* CCITT */ > - len = rose_parse_ccitt(p + 1, facilities, facilities_len - 1); > - if (len < 0) > - return 0; > - facilities_len -= len + 1; > - p += len + 1; > - break; > - > - default: > - printk(KERN_DEBUG "ROSE: rose_parse_facilities - unknown facilities family %02X\n", *p); > - facilities_len--; > - p++; > - break; > - } > - } else > - break; /* Error in facilities format */ > + while (facilities_len >= 3 && *p == 0x00) { > + facilities_len--; > + p++; > + > + switch (*p) { > + case FAC_NATIONAL: /* National */ > + len = rose_parse_national(p + 1, facilities, facilities_len - 1); > + break; > + > + case FAC_CCITT: /* CCITT */ > + len = rose_parse_ccitt(p + 1, facilities, facilities_len - 1); > + break; > + > + default: > + printk(KERN_DEBUG "ROSE: rose_parse_facilities - unknown facilities family %02X\n", *p); > + len = 1; > + break; > + } > + > + if (len < 0) > + return 0; > + if (WARN_ON(len >= facilities_len)) > + return 0; > + facilities_len -= len + 1; > + p += len + 1; > } > > - return 1; > + return facilities_len == 0; > } This last hunk does not look correct. In the default branch of the switch, you set len = 1, which means p += 2; facilities_len -= 2. The original code does facilities_len--; p++; ... and it looks correct. So, to get the old behaviour back: diff --git a/net/rose/rose_subr.c b/net/rose/rose_subr.c index f6c71ca..9777700 100644 --- a/net/rose/rose_subr.c +++ b/net/rose/rose_subr.c @@ -418,7 +418,7 @@ int rose_parse_facilities(unsigned char *p, unsigned packet_len, default: printk(KERN_DEBUG "ROSE: rose_parse_facilities - unknown facilities family %02X\n", *p); - len = 1; + len = 0; break; } However, I wonder how much sense it makes to continue parsing the facilities if an unknown facility family appears. We don't know the length of its data, so we will interpret each 16 bytes a new facilities header, hopefully soon bailing out on *p != 0x00. In case of a long packet where every other byte is zero, the loop will spam the kernel log with the printk ... which could probably be classified as a security problem on its own. So how about the following instead? I have no idea if this breaks some rose specification, though. Signed-off-by: Jiri Bohac diff --git a/net/rose/rose_subr.c b/net/rose/rose_subr.c index f6c71ca..e687c7f 100644 --- a/net/rose/rose_subr.c +++ b/net/rose/rose_subr.c @@ -418,8 +418,7 @@ int rose_parse_facilities(unsigned char *p, unsigned packet_len, default: printk(KERN_DEBUG "ROSE: rose_parse_facilities - unknown facilities family %02X\n", *p); - len = 1; - break; + return 0; } if (len < 0) -- Jiri Bohac SUSE Labs, SUSE CZ