Subject: [PATCH] negative dev use in /proc/net/rose_neigh

From: Bernard Pidoux <[email-masked]>
Date: Sun, 28 Sep 2008 21:56:38 +0200

When running rose network applications, rose_neigh use counter can become negative as shown below.
Number 65535 actually represents a short integer underflow, meaning that use counter has been
decremented while equal to zero.
Then use counter continues to decrease by one each time the function is called.

proc/net/rose_neigh
addr  callsign  dev  count use mode restart  t0  tf digipeaters
00005 F5KCK-11  ax1      4   1  DTE     yes   0   0
00004 F6BVP-5   ax4      6   0  DTE      no   0   0
00003 F6BVP-7   ax4      6   0  DCE     yes   0   0
00002 F6BVP-11  ax4      6 65535  DCE     yes   0   0
00001 RSLOOP-0  ???      1   4  DCE     yes   0   0

After investigations I found that use counter value was going negative when
rose_kill_by_neigh() (in af_rose.c) was called and sk_for_each() macro loop activated
rose->neighbour->use-- more than once.

I propose the following patch to avoid use counter underflow.
However a KERN_WARNING message could be better instead of KERN_ERR.
 
Signed-off-by: Bernard Pidoux <[email-masked]>
---
 net/rose/af_rose.c |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/net/rose/af_rose.c b/net/rose/af_rose.c
index a7f1ce1..8a54cff 100644
--- a/net/rose/af_rose.c
+++ b/net/rose/af_rose.c
@@ -175,7 +175,10 @@ void rose_kill_by_neigh(struct rose_neigh *neigh)
 
 		if (rose->neighbour == neigh) {
 			rose_disconnect(s, ENETUNREACH, ROSE_OUT_OF_ORDER, 0);
-			rose->neighbour->use--;
+			if (rose->neighbour->use > 0 ) 
+				rose->neighbour->use--;
+			else
+				printk(KERN_ERR "ROSE: rose_kill_by_neigh() - neighbour->use-- could be < 0\n");
 			rose->neighbour = NULL;
 		}
 	}
-- 
1.5.5