[PATCH] SCTP: Respect the real chunk length when walking parameters (CVE-2006-1858)

When performing bound checks during the parameter processing, we
want to use the real chunk and paramter lengths for bounds instead
of the rounded ones.  This prevents us from potentially walking of
the end if the chunk length was miscalculated.  We still use rounded
lengths when advancing the pointer. This was found during a
conformance test that changed the chunk length without modifying
parameters.

(Vlad noted elsewhere: the most you'd overflow is 3 bytes, so problem
is parameter dependent).
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>

include/net/sctp/sctp.h

@@ -461,12 +461,12 @@ static inline int sctp_frag_point(const struct sctp_sock *sp, int pmtu)
  * there is room for a param header too.
  */
 #define sctp_walk_params(pos, chunk, member)\
-_sctp_walk_params((pos), (chunk), WORD_ROUND(ntohs((chunk)->chunk_hdr.length)), member)
+_sctp_walk_params((pos), (chunk), ntohs((chunk)->chunk_hdr.length), member)
 
 #define _sctp_walk_params(pos, chunk, end, member)\
 for (pos.v = chunk->member;\
      pos.v <= (void *)chunk + end - sizeof(sctp_paramhdr_t) &&\
-     pos.v <= (void *)chunk + end - WORD_ROUND(ntohs(pos.p->length)) &&\
+     pos.v <= (void *)chunk + end - ntohs(pos.p->length) &&\
      ntohs(pos.p->length) >= sizeof(sctp_paramhdr_t);\
      pos.v += WORD_ROUND(ntohs(pos.p->length)))
 
@@ -477,7 +477,7 @@ _sctp_walk_errors((err), (chunk_hdr), ntohs((chunk_hdr)->length))
 for (err = (sctp_errhdr_t *)((void *)chunk_hdr + \
 	    sizeof(sctp_chunkhdr_t));\
      (void *)err <= (void *)chunk_hdr + end - sizeof(sctp_errhdr_t) &&\
-     (void *)err <= (void *)chunk_hdr + end - WORD_ROUND(ntohs(err->length)) &&\
+     (void *)err <= (void *)chunk_hdr + end - ntohs(err->length) &&\
      ntohs(err->length) >= sizeof(sctp_errhdr_t); \
      err = (sctp_errhdr_t *)((void *)err + WORD_ROUND(ntohs(err->length))))