commit 412cb7a3fb66792f8ec30ed80e126193ad073e56
author Arnd Bergmann <arnd@arndb.de> Wed Apr 29 21:00:41 2020 +0200
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> Thu May 14 07:57:23 2020 +0200
tree e06ef3d1416de63ceca8ee4f85325055353a70d1
parent efc97a1dec84a0f19ad3851014e54306597f2602

netfilter: nf_osf: avoid passing pointer to local var

commit c165d57b552aaca607fa5daf3fb524a6efe3c5a3 upstream.

gcc-10 points out that a code path exists where a pointer to a stack
variable may be passed back to the caller:

net/netfilter/nfnetlink_osf.c: In function 'nf_osf_hdr_ctx_init':
cc1: warning: function may return address of local variable [-Wreturn-local-addr]
net/netfilter/nfnetlink_osf.c:171:16: note: declared here
  171 |  struct tcphdr _tcph;
      |                ^~~~~

I am not sure whether this can happen in practice, but moving the
variable declaration into the callers avoids the problem.

Fixes: 31a9c29210e2 ("netfilter: nf_osf: add struct nf_osf_hdr_ctx")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/netfilter/nfnetlink_osf.c

diff --git a/net/netfilter/nfnetlink_osf.c b/net/netfilter/nfnetlink_osf.c
index b0bc130..131f9f8 100644
--- a/net/netfilter/nfnetlink_osf.c
+++ b/net/netfilter/nfnetlink_osf.c
@@ -170,12 +170,12 @@
 static const struct tcphdr *nf_osf_hdr_ctx_init(struct nf_osf_hdr_ctx *ctx,
 						const struct sk_buff *skb,
 						const struct iphdr *ip,
-						unsigned char *opts)
+						unsigned char *opts,
+						struct tcphdr *_tcph)
 {
 	const struct tcphdr *tcp;
-	struct tcphdr _tcph;
 
-	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), &_tcph);
+	tcp = skb_header_pointer(skb, ip_hdrlen(skb), sizeof(struct tcphdr), _tcph);
 	if (!tcp)
 		return NULL;
 
@@ -210,10 +210,11 @@
 	int fmatch = FMATCH_WRONG;
 	struct nf_osf_hdr_ctx ctx;
 	const struct tcphdr *tcp;
+	struct tcphdr _tcph;
 
 	memset(&ctx, 0, sizeof(ctx));
 
-	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
+	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 	if (!tcp)
 		return false;
 
@@ -270,10 +271,11 @@
 	struct nf_osf_hdr_ctx ctx;
 	const struct tcphdr *tcp;
 	const char *genre = NULL;
+	struct tcphdr _tcph;
 
 	memset(&ctx, 0, sizeof(ctx));
 
-	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts);
+	tcp = nf_osf_hdr_ctx_init(&ctx, skb, ip, opts, &_tcph);
 	if (!tcp)
 		return NULL;