[PATCH net] ipv6: rpl: fix loop iteration

[PATCH net] ipv6: rpl: fix loop iteration

[Alexander Aring]

This patch fix the loop iteration by not walking over the last
iteration. The cmpri compressing value exempt the last segment. As the
code shows the last iteration will be overwritten by cmpre value
handling which is for the last segment.

I think this doesn't end in any bufferoverflows because we work on worst
case temporary buffer sizes but it ends in not best compression settings
in some cases.

Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")
Signed-off-by: Alexander Aring <alex.aring@gmail.com>
---
Sorry, I should have caught this earlier and was sure I tested this code.
It's likely to have a off by one error because sometimes you want to walk
over all segments and sometimes you want to walk over all exempt the last
(because cmpri affects all segments exempt the last one).

 net/ipv6/rpl.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/ipv6/rpl.c b/net/ipv6/rpl.c
index dc4f20e23bf7..d38b476fc7f2 100644
--- a/net/ipv6/rpl.c
+++ b/net/ipv6/rpl.c
@@ -48,7 +48,7 @@ void ipv6_rpl_srh_decompress(struct ipv6_rpl_sr_hdr *outhdr,
 	outhdr->cmpri = 0;
 	outhdr->cmpre = 0;
 
-	for (i = 0; i <= n; i++)
+	for (i = 0; i < n; i++)
 		ipv6_rpl_addr_decompress(&outhdr->rpl_segaddr[i], daddr,
 					 ipv6_rpl_segdata_pos(inhdr, i),
 					 inhdr->cmpri);
@@ -66,7 +66,7 @@ static unsigned char ipv6_rpl_srh_calc_cmpri(const struct ipv6_rpl_sr_hdr *inhdr
 	int i;
 
 	for (plen = 0; plen < sizeof(*daddr); plen++) {
-		for (i = 0; i <= n; i++) {
+		for (i = 0; i < n; i++) {
 			if (daddr->s6_addr[plen] !=
 			    inhdr->rpl_segaddr[i].s6_addr[plen])
 				return plen;
@@ -114,7 +114,7 @@ void ipv6_rpl_srh_compress(struct ipv6_rpl_sr_hdr *outhdr,
 	outhdr->cmpri = cmpri;
 	outhdr->cmpre = cmpre;
 
-	for (i = 0; i <= n; i++)
+	for (i = 0; i < n; i++)
 		ipv6_rpl_addr_compress(ipv6_rpl_segdata_pos(outhdr, i),
 				       &inhdr->rpl_segaddr[i], cmpri);
 
-- 
2.20.1

Re: [PATCH net] ipv6: rpl: fix loop iteration

[David Miller]

From: Alexander Aring <alex.aring@gmail.com>
Date: Sat,  4 Apr 2020 11:22:57 -0400

> This patch fix the loop iteration by not walking over the last
> iteration. The cmpri compressing value exempt the last segment. As the
> code shows the last iteration will be overwritten by cmpre value
> handling which is for the last segment.
> 
> I think this doesn't end in any bufferoverflows because we work on worst
> case temporary buffer sizes but it ends in not best compression settings
> in some cases.
> 
> Fixes: 8610c7c6e3bd ("net: ipv6: add support for rpl sr exthdr")
> Signed-off-by: Alexander Aring <alex.aring@gmail.com>

Applied, thanks.