[PATCH 6/6] backports: genetlink: avoid NULL dereference

From: Johannes Berg <[email protected]>

If we fail to allocate extack, we fall back to the code path
that tries to send an error *with* extack, but that will
access our extack pointer. It also doesn't make sense, so just
return an error back to netlink immediately and let it handle
sending the error message to userspace.

Signed-off-by: Johannes Berg <[email protected]>
Signed-off-by: Luca Coelho <[email protected]>
---
 backport/compat/backport-genetlink.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/backport/compat/backport-genetlink.c b/backport/compat/backport-genetlink.c
index 71bf45adf88d..885f17568333 100644
--- a/backport/compat/backport-genetlink.c
+++ b/backport/compat/backport-genetlink.c
@@ -157,12 +157,10 @@ static int backport_pre_doit(__genl_const struct genl_ops *ops,
 #if LINUX_VERSION_IS_LESS(4,12,0)
 	struct netlink_ext_ack *extack = kzalloc(sizeof(*extack), GFP_KERNEL);
 
-	__bp_genl_info_userhdr_set(info, extack);
+	if (!extack)
+		return -ENOMEM;
 
-	if (!extack) {
-		err = -ENOMEM;
-		goto err;
-	}
+	__bp_genl_info_userhdr_set(info, extack);
 
 	extack->__bp_doit = ops->doit;
 #else
@@ -175,7 +173,6 @@ static int backport_pre_doit(__genl_const struct genl_ops *ops,
 		err = family->pre_doit(ops, skb, info);
 
 #if LINUX_VERSION_IS_LESS(4,12,0)
-err:
 	if (err) {
 		/* signal to do nothing */
 		extack->__bp_doit = NULL;
-- 
2.20.1

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