[PATCH] nl80211: check return of nla_parse_nested

[PATCH] nl80211: check return of nla_parse_nested

[trix]

From: Tom Rix <trix@redhat.com>

Clang static analysis reports this representative problem
nl80211.c:15426:6: warning: Branch condition evaluates
  to a garbage value
  if (!tb[NL80211_SAR_ATTR_TYPE] ||
       ^~~~~~~~~~~~~~~~~~~~~~~~~~

tb is set when nla_parse_nested() is successful.
So check.

Fixes: 6bdb68cef7bf ("nl80211: add common API to configure SAR power limitations")
Signed-off-by: Tom Rix <trix@redhat.com>
---
 net/wireless/nl80211.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 7543c73a3f1d..c1532c8eb657 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -15419,9 +15419,11 @@ static int nl80211_set_sar_specs(struct sk_buff *skb, struct genl_info *info)
 	if (!info->attrs[NL80211_ATTR_SAR_SPEC])
 		return -EINVAL;
 
-	nla_parse_nested(tb, NL80211_SAR_ATTR_MAX,
-			 info->attrs[NL80211_ATTR_SAR_SPEC],
-			 NULL, NULL);
+	err = nla_parse_nested(tb, NL80211_SAR_ATTR_MAX,
+			       info->attrs[NL80211_ATTR_SAR_SPEC],
+			       NULL, NULL);
+	if (err)
+		return err;
 
 	if (!tb[NL80211_SAR_ATTR_TYPE] || !tb[NL80211_SAR_ATTR_SPECS])
 		return -EINVAL;
@@ -15444,8 +15446,10 @@ static int nl80211_set_sar_specs(struct sk_buff *skb, struct genl_info *info)
 	sar_spec->type = type;
 	specs = 0;
 	nla_for_each_nested(spec_list, tb[NL80211_SAR_ATTR_SPECS], rem) {
-		nla_parse_nested(spec, NL80211_SAR_ATTR_SPECS_MAX,
-				 spec_list, NULL, NULL);
+		err = nla_parse_nested(spec, NL80211_SAR_ATTR_SPECS_MAX,
+				       spec_list, NULL, NULL);
+		if (err)
+			goto error;
 
 		switch (type) {
 		case NL80211_SAR_TYPE_POWER:
-- 
2.26.3

Re: [PATCH] nl80211: check return of nla_parse_nested

[Johannes Berg]

On Fri, 2022-02-18 at 08:30 -0800, trix@redhat.com wrote:
> From: Tom Rix <trix@redhat.com>
> 
> Clang static analysis reports this representative problem
> nl80211.c:15426:6: warning: Branch condition evaluates
>   to a garbage value
>   if (!tb[NL80211_SAR_ATTR_TYPE] ||
>        ^~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> tb is set when nla_parse_nested() is successful.
> So check.

Well, it's a bit annoying that we cannot express/check this, but we
already validated that it's going to succeed, through the nested policy:

static const struct nla_policy nl80211_policy[NUM_NL80211_ATTR] = {
[...]
        [NL80211_ATTR_SAR_SPEC] = NLA_POLICY_NESTED(sar_policy),


Thus, it cannot actually fail. I suppose in this case checking for
errors doesn't make the code that much worse, but there's isn't really
much point. Maybe a comment would be useful?

johannes