Linux Ethernet Bridging - Jul 2019 - [Bridge] [PATCH] netfilter: ebtables: compat: fix a memory leak bug

From: Wenwen Wang <wenwen at cs.uga.edu>

In compat_do_replace(), a temporary buffer is allocated through vmalloc()
to hold entries copied from the user space. The buffer address is firstly
saved to 'newinfo->entries', and later on assigned to
'entries_tmp'. Then
the entries in this temporary buffer is copied to the internal kernel
structure through compat_copy_entries(). If this copy process fails,
compat_do_replace() should be terminated. However, the allocated temporary
buffer is not freed on this path, leading to a memory leak.

To fix the bug, free the buffer before returning from compat_do_replace().

Signed-off-by: Wenwen Wang <wenwen at cs.uga.edu>
---
 net/bridge/netfilter/ebtables.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 963dfdc..fd84b48e 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -2261,8 +2261,10 @@ static int compat_do_replace(struct net *net, void __user
*user,
 	state.buf_kern_len = size64;
 
 	ret = compat_copy_entries(entries_tmp, tmp.entries_size, &state);
-	if (WARN_ON(ret < 0))
+	if (WARN_ON(ret < 0)) {
+		vfree(entries_tmp);
 		goto out_unlock;
+	}
 
 	vfree(entries_tmp);
 	tmp.entries_size = size64;
-- 
2.7.4

Wenwen Wang <wang6495 at umn.edu> wrote:
> From: Wenwen Wang <wenwen at cs.uga.edu>
> 
> In compat_do_replace(), a temporary buffer is allocated through vmalloc()
> to hold entries copied from the user space. The buffer address is firstly
> saved to 'newinfo->entries', and later on assigned to
'entries_tmp'. Then
> the entries in this temporary buffer is copied to the internal kernel
> structure through compat_copy_entries(). If this copy process fails,
> compat_do_replace() should be terminated. However, the allocated temporary
> buffer is not freed on this path, leading to a memory leak.
> 
> To fix the bug, free the buffer before returning from compat_do_replace().
> 
> Signed-off-by: Wenwen Wang <wenwen at cs.uga.edu>
Reviewed-by: Florian Westphal <fw at strlen.de>

On Sat, Jul 20, 2019 at 07:22:45AM -0500, Wenwen Wang
wrote:
> From: Wenwen Wang <wenwen at cs.uga.edu>
> 
> In compat_do_replace(), a temporary buffer is allocated through vmalloc()
> to hold entries copied from the user space. The buffer address is firstly
> saved to 'newinfo->entries', and later on assigned to
'entries_tmp'. Then
> the entries in this temporary buffer is copied to the internal kernel
> structure through compat_copy_entries(). If this copy process fails,
> compat_do_replace() should be terminated. However, the allocated temporary
> buffer is not freed on this path, leading to a memory leak.
> 
> To fix the bug, free the buffer before returning from compat_do_replace().
Applied, thanks.