linux-kernel - Re: [PATCH] sctp: prevent reading out-of-bounds memory

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Message-ID: <AANLkTikRBOhTQM0gyS8_Vwu7EsetaaaEuv0owkBp7B_F@mail.gmail.com>
Date:	Fri, 3 Sep 2010 10:35:15 -0400
From:	Dan Rosenberg <dan.j.rosenberg@...il.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
Cc:	sri@...ibm.com, linux-sctp@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sctp: prevent reading out-of-bounds memory

Ha, I knew there was an easier way.  Take two:

Signed-off-by: Dan Rosenberg <dan.j.rosenberg@...il.com>

--- linux-2.6.35.4.orig/net/sctp/socket.c	2010-09-03 08:58:48.127080114 -0400
+++ linux-2.6.35.4/net/sctp/socket.c	2010-09-03 10:28:14.929595312 -0400
@@ -916,6 +916,12 @@ SCTP_STATIC int sctp_setsockopt_bindx(st
 	/* Walk through the addrs buffer and count the number of addresses. */
 	addr_buf = kaddrs;
 	while (walk_size < addrs_size) {
+
+		if (walk_size + sizeof(sa_family_t) > addrs_size) {
+			kfree(kaddrs);
+			return -EINVAL;
+		}
+
 		sa_addr = (struct sockaddr *)addr_buf;
 		af = sctp_get_af_specific(sa_addr->sa_family);

@@ -1002,6 +1008,12 @@ static int __sctp_connect(struct sock* s
 	/* Walk through the addrs buffer and count the number of addresses. */
 	addr_buf = kaddrs;
 	while (walk_size < addrs_size) {
+
+		if (walk_size + sizeof(sa_family_t) > addrs_size) {
+			err = -EINVAL;
+			goto out_free;
+		}
+
 		sa_addr = (union sctp_addr *)addr_buf;
 		af = sctp_get_af_specific(sa_addr->sa.sa_family);
 		port = ntohs(sa_addr->v4.sin_port);


>
> Hm.. we already validate that we have the proper amount of space for a given sockaddr.
> The only thing we are missing is making sure that there is room to get the proper address
> family and I think you can do that without adding any extra variables:
>
>        if (walk_size + sizeof(sa_family_t) > addr_size) {
>                /* Not enough room for address family */
>                kfree(kaddrs);
>                return -EINVAL;
>        }
>
> -vlad
>

On Fri, Sep 3, 2010 at 10:15 AM, Vlad Yasevich
<vladislav.yasevich@...com> wrote:
> On 09/03/2010 09:48 AM, Dan Rosenberg wrote:
>> Two user-controlled allocations in SCTP are subsequently dereferenced
>> as sockaddr structs, without checking if the dereferenced struct
>> members fall beyond the end of the allocated chunk.  There doesn't
>> appear to be any information leakage here based on how these members
>> are used and additional checking, but it's still worth fixing.
>>
>> Signed-off-by: Dan Rosenberg <dan.j.rosenberg@...il.com>
>>
>> --- linux-2.6.35.4.orig/net/sctp/socket.c     2010-09-03 08:58:48.127080114 -0400
>> +++ linux-2.6.35.4/net/sctp/socket.c  2010-09-03 09:22:06.337096825 -0400
>> @@ -889,6 +889,7 @@ SCTP_STATIC int sctp_setsockopt_bindx(st
>>       int err;
>>       int addrcnt = 0;
>>       int walk_size = 0;
>> +     unsigned int remaining = addrs_size;
>>       struct sockaddr *sa_addr;
>>       void *addr_buf;
>>       struct sctp_af *af;
>> @@ -916,6 +917,13 @@ SCTP_STATIC int sctp_setsockopt_bindx(st
>>       /* Walk through the addrs buffer and count the number of addresses. */
>>       addr_buf = kaddrs;
>>       while (walk_size < addrs_size) {
>> +
>> +             /* Don't read out-of-bounds memory */
>> +             if (remaining < sizeof(struct sockaddr)) {
>> +                     kfree(kaddrs);
>> +                     return -EINVAL;
>> +             }
>> +
>>               sa_addr = (struct sockaddr *)addr_buf;
>>               af = sctp_get_af_specific(sa_addr->sa_family);
>>
>> @@ -929,6 +937,7 @@ SCTP_STATIC int sctp_setsockopt_bindx(st
>>               addrcnt++;
>>               addr_buf += af->sockaddr_len;
>>               walk_size += af->sockaddr_len;
>> +             remaining -= af->sockaddr_len;
>>       }
>>
>>       /* Do the work. */
>> @@ -984,6 +993,7 @@ static int __sctp_connect(struct sock* s
>>       void *addr_buf;
>>       unsigned short port;
>>       unsigned int f_flags = 0;
>> +     unsigned int remaining = addrs_size;
>>
>>       sp = sctp_sk(sk);
>>       ep = sp->ep;
>> @@ -1002,6 +1012,13 @@ static int __sctp_connect(struct sock* s
>>       /* Walk through the addrs buffer and count the number of addresses. */
>>       addr_buf = kaddrs;
>>       while (walk_size < addrs_size) {
>> +
>> +             /* Don't read out-of-bounds memory */
>> +             if (remaining < sizeof(union sctp_addr)) {
>> +                     err = -EINVAL;
>> +                     goto out_free;
>> +             }
>> +
>>               sa_addr = (union sctp_addr *)addr_buf;
>>               af = sctp_get_af_specific(sa_addr->sa.sa_family);
>>               port = ntohs(sa_addr->v4.sin_port);
>> @@ -1101,6 +1118,7 @@ static int __sctp_connect(struct sock* s
>>               addrcnt++;
>>               addr_buf += af->sockaddr_len;
>>               walk_size += af->sockaddr_len;
>> +             remaining -= af->sockaddr_len;
>>       }
>>
>>       /* In case the user of sctp_connectx() wants an association
>>
>
>
--
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