[34-longterm 001/260] sctp: fix append error cause to ERROR chunk correctly

[Paul Gortmaker]

From: Wei Yongjun <yjwei@xxxxxxxxxxxxxx>

commit 2e3219b5c8a2e44e0b83ae6e04f52f20a82ac0f2 upstream.

commit 5fa782c2f5ef6c2e4f04d3e228412c9b4a4c8809
  sctp: Fix skb_over_panic resulting from multiple invalid \
    parameter errors (CVE-2010-1173) (v4)

cause 'error cause' never be add the the ERROR chunk due to
some typo when check valid length in sctp_init_cause_fixed().

Signed-off-by: Wei Yongjun <yjwei@xxxxxxxxxxxxxx>
Reviewed-by: Neil Horman <nhorman@xxxxxxxxxxxxx>
Acked-by: Vlad Yasevich <vladislav.yasevich@xxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 net/sctp/sm_make_chunk.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
index 30c1767..70d6c10 100644
--- a/net/sctp/sm_make_chunk.c
+++ b/net/sctp/sm_make_chunk.c
@@ -141,7 +141,7 @@ int sctp_init_cause_fixed(struct sctp_chunk *chunk, __be16 cause_code,
 	len = sizeof(sctp_errhdr_t) + paylen;
 	err.length  = htons(len);
 
-	if (skb_tailroom(chunk->skb) >  len)
+	if (skb_tailroom(chunk->skb) < len)
 		return -ENOSPC;
 	chunk->subh.err_hdr = sctp_addto_chunk_fixed(chunk,
 						     sizeof(sctp_errhdr_t),
@@ -1421,7 +1421,7 @@ void *sctp_addto_chunk(struct sctp_chunk *chunk, int len, const void *data)
 void *sctp_addto_chunk_fixed(struct sctp_chunk *chunk,
 			     int len, const void *data)
 {
-	if (skb_tailroom(chunk->skb) > len)
+	if (skb_tailroom(chunk->skb) >= len)
 		return sctp_addto_chunk(chunk, len, data);
 	else
 		return NULL;
-- 
1.7.3.3

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