[PATCH v2 1/1] net: netlink: Fix multicast group storage allocation for families with more than one groups

[PATCH v2 1/1] net: netlink: Fix multicast group storage allocation for families with more than one groups

[Matti Vaittinen]

Hello again,

      Second version, Fixed the 'off by one' bug spotted by David.

      Br.
        Matti Vaittinen

Multicast groups are stored in global buffer. Check for needed buffer size
incorrectly compares buffer size to first id for family. This means that
for families with more than one mcast id one may allocate too small buffer
and end up writing rest of the groups to some unallocated memory. Fix the
buffer size check to compare allocated space to last mcast id for the
family.

Tested on ARM using kernel 3.14

Signed-off-by: Matti Vaittinen <matti.vaittinen@nokia.com>
---
 net/netlink/genetlink.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/genetlink.c b/net/netlink/genetlink.c
index bc0e504..5e113ba 100644
--- a/net/netlink/genetlink.c
+++ b/net/netlink/genetlink.c
@@ -185,7 +185,7 @@ static int genl_allocate_reserve_groups(int n_groups, int *first_id)
 			}
 		}
 
-		if (id >= mc_groups_longs * BITS_PER_LONG) {
+		if (id + n_groups > mc_groups_longs * BITS_PER_LONG) {
 			unsigned long new_longs = mc_groups_longs +
 						  BITS_TO_LONGS(n_groups);
 			size_t nlen = new_longs * sizeof(unsigned long);
-- 
2.1.0

Re: [PATCH v2 1/1] net: netlink: Fix multicast group storage allocation for families with more than one groups

[David Miller]

From: Matti Vaittinen <matti.vaittinen@nokia.com>
Date: Wed, 13 Jan 2016 09:54:12 +0200

> Hello again,
> 
>       Second version, Fixed the 'off by one' bug spotted by David.
> 
>       Br.
>         Matti Vaittinen
> 
> Multicast groups are stored in global buffer. Check for needed buffer size
> incorrectly compares buffer size to first id for family. This means that
> for families with more than one mcast id one may allocate too small buffer
> and end up writing rest of the groups to some unallocated memory. Fix the
> buffer size check to compare allocated space to last mcast id for the
> family.
> 
> Tested on ARM using kernel 3.14
> 
> Signed-off-by: Matti Vaittinen <matti.vaittinen@nokia.com>

I inadvertantly applied your original patch, so I'll just fix
the off-by-one error with a seperate commit.

Sorry for the confusion and thanks for fixing this.