netdev - Re: [PATCH] sctp: fix -ENOMEM result with invalid user space pointer in sendto() syscall

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Date:	Mon, 26 Nov 2012 10:25:34 -0500
From:	Neil Horman <nhorman@...driver.com>
To:	Tommi Rantala <tt.rantala@...il.com>
Cc:	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	Vlad Yasevich <vyasevich@...il.com>,
	Sridhar Samudrala <sri@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH] sctp: fix -ENOMEM result with invalid user space pointer
 in sendto() syscall

On Thu, Nov 22, 2012 at 03:23:16PM +0200, Tommi Rantala wrote:
> Consider the following program, that sets the second argument to the
> sendto() syscall incorrectly:
> 
>  #include <string.h>
>  #include <arpa/inet.h>
>  #include <sys/socket.h>
> 
>  int main(void)
>  {
>          int fd;
>          struct sockaddr_in sa;
> 
>          fd = socket(AF_INET, SOCK_STREAM, 132 /*IPPROTO_SCTP*/);
>          if (fd < 0)
>                  return 1;
> 
>          memset(&sa, 0, sizeof(sa));
>          sa.sin_family = AF_INET;
>          sa.sin_addr.s_addr = inet_addr("127.0.0.1");
>          sa.sin_port = htons(11111);
> 
>          sendto(fd, NULL, 1, 0, (struct sockaddr *)&sa, sizeof(sa));
> 
>          return 0;
>  }
> 
> We get -ENOMEM:
> 
>  $ strace -e sendto ./demo
>  sendto(3, NULL, 1, 0, {sa_family=AF_INET, sin_port=htons(11111), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 ENOMEM (Cannot allocate memory)
> 
> Propagate the error code from sctp_user_addto_chunk(), so that we will
> tell user space what actually went wrong:
> 
>  $ strace -e sendto ./demo
>  sendto(3, NULL, 1, 0, {sa_family=AF_INET, sin_port=htons(11111), sin_addr=inet_addr("127.0.0.1")}, 16) = -1 EFAULT (Bad address)
> 
> Noticed while running Trinity (the syscall fuzzer).
> 
> Signed-off-by: Tommi Rantala <tt.rantala@...il.com>
> ---
>  net/sctp/chunk.c  |   13 +++++++++----
>  net/sctp/socket.c |    4 ++--
>  2 files changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/net/sctp/chunk.c b/net/sctp/chunk.c
> index d241ef5..3952ca9 100644
> --- a/net/sctp/chunk.c
> +++ b/net/sctp/chunk.c
> @@ -183,7 +183,7 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
>  
>  	msg = sctp_datamsg_new(GFP_KERNEL);
>  	if (!msg)
> -		return NULL;
> +		return ERR_PTR(-ENOMEM);
>  
>  	/* Note: Calculate this outside of the loop, so that all fragments
>  	 * have the same expiration.
> @@ -280,8 +280,11 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
>  
>  		chunk = sctp_make_datafrag_empty(asoc, sinfo, len, frag, 0);
>  
> -		if (!chunk)
> +		if (!chunk) {
> +			err = -ENOMEM;
>  			goto errout;
> +		}
> +
>  		err = sctp_user_addto_chunk(chunk, offset, len, msgh->msg_iov);
>  		if (err < 0)
>  			goto errout_chunk_put;
> @@ -315,8 +318,10 @@ struct sctp_datamsg *sctp_datamsg_from_user(struct sctp_association *asoc,
>  
>  		chunk = sctp_make_datafrag_empty(asoc, sinfo, over, frag, 0);
>  
> -		if (!chunk)
> +		if (!chunk) {
> +			err = -ENOMEM;
>  			goto errout;
> +		}
>  
>  		err = sctp_user_addto_chunk(chunk, offset, over,msgh->msg_iov);
>  
> @@ -342,7 +347,7 @@ errout:
>  		sctp_chunk_free(chunk);
>  	}
>  	sctp_datamsg_put(msg);
> -	return NULL;
> +	return ERR_PTR(err);
>  }
>  
>  /* Check whether this message has expired. */
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index a60d1f8..406d957 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -1915,8 +1915,8 @@ SCTP_STATIC int sctp_sendmsg(struct kiocb *iocb, struct sock *sk,
>  
>  	/* Break the message into multiple chunks of maximum size. */
>  	datamsg = sctp_datamsg_from_user(asoc, sinfo, msg, msg_len);
> -	if (!datamsg) {
> -		err = -ENOMEM;
> +	if (IS_ERR(datamsg)) {
> +		err = PTR_ERR(datamsg);
>  		goto out_free;
>  	}
>  
> -- 
> 1.7.9.5
> 
> --
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> 
Acked-by: Neil Horman <nhorman@...driver.com>

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