Subject: Re: [PATCH] ROSE: prevent heap corruption with bad facilities

From: Dan Rosenberg <[email-masked]>
Date: Sun, 20 Mar 2011 02:03:24 -0400

On Sat, 2011-03-19 at 19:28 -0400, Dan Rosenberg wrote:
> When parsing the FAC_NATIONAL_DIGIS facilities field, keeping the
> counter field in an unsigned char is insufficient, since the counter is
> incremented by AX25_ADDR_LEN (7) with each loop.  Providing a field
> length of 0xf, for example, causes heap corruption because the counter
> wraps without ever reaching the length and data is copied past the
> boundaries of the source_digis or dest_digis facilities arrays.  Change
> the counter to an unsigned ints to prevent this wrapping and overflow.
> 
> Additionally, when parsing the FAC_CCITT_DEST_NSAP and
> FAC_CCITT_SRC_NSAP facilities fields, a length of less than 10 results
> in an underflow in a memcpy size, resulting in a kernel panic due to
> massive heap corruption.  Abort facilities parsing on this invalid
> length value.

Please disregard this patch, my brain wasn't working properly when I
wrote it.  There are problems in these areas, but this fix is incomplete
(and the description for the first issue is practically nonsensical).
I'll resend a new version shortly.

> 
> Signed-off-by: Dan Rosenberg <[email-masked]>
> Cc: [email-masked]
> ---
>  net/rose/rose_subr.c |   12 +++++++++++-
>  1 files changed, 11 insertions(+), 1 deletions(-)
> 
> diff --git a/net/rose/rose_subr.c b/net/rose/rose_subr.c
> index 1734abb..fee9de4 100644
> --- a/net/rose/rose_subr.c
> +++ b/net/rose/rose_subr.c
> @@ -240,7 +240,8 @@ int rose_decode(struct sk_buff *skb, int *ns, int *nr, int *q, int *d, int *m)
>  static int rose_parse_national(unsigned char *p, struct rose_facilities_struct *facilities, int len)
>  {
>  	unsigned char *pt;
> -	unsigned char l, lg, n = 0;
> +	unsigned char l, n = 0;
> +	unsigned int lg;
>  	int fac_national_digis_received = 0;
>  
>  	do {
> @@ -334,12 +335,16 @@ static int rose_parse_ccitt(unsigned char *p, struct rose_facilities_struct *fac
>  		case 0xC0:
>  			l = p[1];
>  			if (*p == FAC_CCITT_DEST_NSAP) {
> +				if (l < 10)
> +					return -1;
>  				memcpy(&facilities->source_addr, p + 7, ROSE_ADDR_LEN);
>  				memcpy(callsign, p + 12,   l - 10);
>  				callsign[l - 10] = '\0';
>  				asc2ax(&facilities->source_call, callsign);
>  			}
>  			if (*p == FAC_CCITT_SRC_NSAP) {
> +				if (l < 10)
> +					return -1;
>  				memcpy(&facilities->dest_addr, p + 7, ROSE_ADDR_LEN);
>  				memcpy(callsign, p + 12, l - 10);
>  				callsign[l - 10] = '\0';
> @@ -379,6 +384,11 @@ int rose_parse_facilities(unsigned char *p,
>  
>  			case FAC_CCITT:		/* CCITT */
>  				len = rose_parse_ccitt(p + 1, facilities, facilities_len - 1);
> +
> +				/* Invalid facilities */
> +				if (len < 0)
> +					return 0;
> +
>  				facilities_len -= len + 1;
>  				p += len + 1;
>  				break;
>