Patch "ipv4: off-by-one in continuation handling in /proc/net/route" has been added to the 4.1-stable tree

This is a note to let you know that I've just added the patch titled

ipv4: off-by-one in continuation handling in /proc/net/route

to the 4.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
ipv4-off-by-one-in-continuation-handling-in-proc-net-route.patch
and it can be found in the queue-4.1 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andy Whitcroft <[email protected]>
Date: Thu, 13 Aug 2015 20:49:01 +0100
Subject: ipv4: off-by-one in continuation handling in /proc/net/route

From: Andy Whitcroft <[email protected]>

[ Upstream commit 25b97c016b26039982daaa2c11d83979f93b71ab ]

When generating /proc/net/route we emit a header followed by a line for each route. When a short read is performed we will restart this process based on the open file descriptor. When calculating the start point we fail to take into account that the 0th entry is the header. This leads us to skip the first entry when doing a continuation read.

This can be easily seen with the comparison below:

while read l; do echo "$l"; done </proc/net/route >A cat /proc/net/route >B
diff -bu A B | grep '^[+-]'

On my example machine I have approximatly 10KB of route output. There we see the very first non-title element is lost in the while read case, and an entry around the 8K mark in the cat case:

+wlan0 00000000 02021EAC 0003 0 0 400 00000000 0 0 0 -tun1 00C0AC0A 00000000 0001 0 0 950 00C0FFFF 0 0 0

Fix up the off-by-one when reaquiring position on continuation.

---
 net/ipv4/fib_trie.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -2453,7 +2453,7 @@ static struct key_vector *fib_route_get_
 		key = l->key + 1;
 		iter->pos++;
 
-		if (pos-- <= 0)
+		if (--pos <= 0)
 			break;
 
 		l = NULL;

Patches currently in stable-queue which might be from [email protected] are

queue-4.1/ipv4-off-by-one-in-continuation-handling-in-proc-net-route.patch