Re: Memory corruption in nfs3_xdr_setaclargs()

["Sachin S. Prabhu" <sprabhu@redhat.com>]

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Trond Myklebust wrote:
> On Tue, 2009-01-20 at 17:14 +0000, Sachin S. Prabhu wrote:
>> A mistake in calculating the space left in the header in nfs3_xdr_setaclargs()
>> can cause memory corruption when setting a large number of acls.
>>
>> Reproducer:
>>
>> On Server:
>> 1) Create directory /test and set mode 777.
>> mkdir /test; chmod 777 /test
>> 2) Add 200 users and set default acl for user on /test
>> for i in {1..200}; do echo $i; useradd user$i; setfacl -m d:u:user$i:rwx
>> /test;done
>> 3) Add export /test  in /etc/exports
>> /test *(rw)
>>
>> On client
>> 1) Mount server:/test
>> mount server:/test /mnt
>> 2) Create large number of directories on the the share.
>> cd/mnt; for i in {1..1000}; do mkdir $i; done
>> At this point, the client should crash.
>>
>> A change in call_header changes the value req->rq_snd_buf->head[0]->iov_len to
>> reflect the exact size of the header.
>> [PATCH] RPC: Ensure XDR iovec length is initialized correctly in call_header
>> 334ccfd545bba9690515f2c5c167d5adb161989b
>>
>> The iov_len is set to the size of the header in  call_header().
>> req->rq_slen = xdr_adjust_iovec(&req->rq_svec[0], p);
>>
>> nfs3_xdr_setaclargs() depends on the older behavior and uses this value when
>> calculating the number of ACLs it can fit into the header.
>>
>>         /* put as much of the acls into head as possible. */
>>         len_in_head = min_t(unsigned int, buf->head->iov_len - base, len);
>>         len -= len_in_head;
>>         req->rq_slen = xdr_adjust_iovec(req->rq_svec, p + (len_in_head >> 2));
>>
>> Since at this stage, iov_len < base, len_in_head will always be set to len. For
>> a large number of ACLs, this will end up over-writing other parts of memory on
>> the nfs client.
>>
>> The following patch which set len_in_head to 0 was tested with the reproducer
>> and was found to fix the problem.
>>
> 
> Looks alright. Could you please add a s-o-b line?
> 
> Cheers
>   Trond
> 

Signed-off-by: Kevin Rudd <solgato@us.ibm.com>

--- fs/nfs/nfs3xdr.c.orig	2009-01-21 13:09:50.000000000 +0000
+++ fs/nfs/nfs3xdr.c	2009-01-21 13:12:11.000000000 +0000
@@ -712,7 +712,10 @@ nfs3_xdr_setaclargs(struct rpc_rqst *req
 	*p++ = htonl(args->mask);
 	base = (char *)p - (char *)buf->head->iov_base;
 	/* put as much of the acls into head as possible. */
-	len_in_head = min_t(unsigned int, buf->head->iov_len - base, len);
+	if ( buf->head->iov_len > base )
+		len_in_head = min_t(unsigned int, buf->head->iov_len - base, len);
+	else
+		len_in_head = 0;
 	len -= len_in_head;
 	req->rq_slen = xdr_adjust_iovec(req->rq_svec, p + (len_in_head >> 2));



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