[PATCH nft] mnl: silence compiler warning

[PATCH nft] mnl: silence compiler warning

[Florian Westphal]

gcc 14.3.0 reports this:

src/mnl.c: In function 'mnl_nft_chain_add':
src/mnl.c:916:25: warning: 'nest' may be used uninitialized [-Wmaybe-uninitialized]
  916 |                         mnl_attr_nest_end(nlh, nest);

I guess its because compiler can't know that the conditions cannot change
in-between and assumes nest_end() can be called without nest_start().

Fixes: 01277922fede ("src: ensure chain policy evaluation when specified")
Signed-off-by: Florian Westphal <fw@strlen.de>
---
 src/mnl.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/src/mnl.c b/src/mnl.c
index ceb43b06690c..6684029606e5 100644
--- a/src/mnl.c
+++ b/src/mnl.c
@@ -890,7 +890,7 @@ int mnl_nft_chain_add(struct netlink_ctx *ctx, struct cmd *cmd,
 	nftnl_chain_nlmsg_build_payload(nlh, nlc);
 
 	if (cmd->chain && cmd->chain->flags & CHAIN_F_BASECHAIN) {
-		struct nlattr *nest;
+		struct nlattr *nest = NULL;
 
 		if (cmd->chain->type.str) {
 			cmd_add_loc(cmd, nlh, &cmd->chain->type.loc);
@@ -911,8 +911,7 @@ int mnl_nft_chain_add(struct netlink_ctx *ctx, struct cmd *cmd,
 		if (cmd->chain && cmd->chain->dev_expr)
 			mnl_nft_chain_devs_build(nlh, cmd);
 
-		if (cmd->chain->type.str ||
-		    (cmd->chain && cmd->chain->dev_expr))
+		if (nest)
 			mnl_attr_nest_end(nlh, nest);
 	}
 
-- 
2.49.1

Re: [PATCH nft] mnl: silence compiler warning

[Pablo Neira Ayuso]

On Wed, Aug 20, 2025 at 02:44:43PM +0200, Florian Westphal wrote:
> gcc 14.3.0 reports this:
> 
> src/mnl.c: In function 'mnl_nft_chain_add':
> src/mnl.c:916:25: warning: 'nest' may be used uninitialized [-Wmaybe-uninitialized]
>   916 |                         mnl_attr_nest_end(nlh, nest);
> 
> I guess its because compiler can't know that the conditions cannot change
> in-between and assumes nest_end() can be called without nest_start().
> 
> Fixes: 01277922fede ("src: ensure chain policy evaluation when specified")
> Signed-off-by: Florian Westphal <fw@strlen.de>

Thanks for this fix.

Reviewed-by: Pablo Neira Ayuso <pablo@netfilter.org>