2021-03-30 17:24:25

by Alaa Emad

Subject: [PATCH v2] wireless/nl80211.c: fix uninitialized variable

This change fix KMSAN uninit-value in net/wireless/nl80211.c:225 , That
because of `fixedlen` variable uninitialized,So I initialized it by zero.

Reported-by: [email protected]
Signed-off-by: Alaa Emad <[email protected]>
---
Changes in v2:
- Make the commit message more clearer.
---
net/wireless/nl80211.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 775d0c4d86c3..b87ab67ad33d 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -210,7 +210,7 @@ static int validate_beacon_head(const struct nlattr *attr,
const struct element *elem;
const struct ieee80211_mgmt *mgmt = (void *)data;
bool s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
- unsigned int fixedlen, hdrlen;
+ unsigned int fixedlen = 0, hdrlen;

if (s1g_bcn) {
fixedlen = offsetof(struct ieee80211_ext,
--
2.25.1

2021-03-30 19:31:12

by Eric Dumazet

Subject: Re: [PATCH v2] wireless/nl80211.c: fix uninitialized variable

On 3/30/21 7:22 PM, Alaa Emad wrote:
> This change fix KMSAN uninit-value in net/wireless/nl80211.c:225 , That
> because of `fixedlen` variable uninitialized,So I initialized it by zero.
>
> Reported-by: [email protected]
> Signed-off-by: Alaa Emad <[email protected]>
> ---
> Changes in v2:
> - Make the commit message more clearer.
> ---
> net/wireless/nl80211.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
> index 775d0c4d86c3..b87ab67ad33d 100644
> --- a/net/wireless/nl80211.c
> +++ b/net/wireless/nl80211.c
> @@ -210,7 +210,7 @@ static int validate_beacon_head(const struct nlattr *attr,
> const struct element *elem;
> const struct ieee80211_mgmt *mgmt = (void *)data;
> bool s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
> - unsigned int fixedlen, hdrlen;
> + unsigned int fixedlen = 0, hdrlen;
>
> if (s1g_bcn) {
> fixedlen = offsetof(struct ieee80211_ext,
>

What was the report exactly ?

Current code does :

unsigned int fixedlen;

if (s1g_bcn) {
fixedlen = something1;
...
else {
fixedlen = something2;
...
}

So your patch does nothing.

Initial value of @fixedlen is not relevant.

Reading this code (without access to KMSAN report) I suspect the issue
is more like the following :

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index 775d0c4d86c3..d815261917ff 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -209,9 +209,12 @@ static int validate_beacon_head(const struct nlattr *attr,
unsigned int len = nla_len(attr);
const struct element *elem;
const struct ieee80211_mgmt *mgmt = (void *)data;
- bool s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
unsigned int fixedlen, hdrlen;
+ bool s1g_bcn;

+ if (len < offsetofend(typeof(*mgmt), frame_control))
+ goto err;
+ s1g_bcn = ieee80211_is_s1g_beacon(mgmt->frame_control);
if (s1g_bcn) {
fixedlen = offsetof(struct ieee80211_ext,
u.s1g_beacon.variable);