[PATCH net] ipv6: Fix may be used uninitialized warning in rt6_check

rt_cookie might be used uninitialized, fix this by
initializing it.

Fixes: c5cff8561d2d ("ipv6: add rcu grace period before freeing fib6_node")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index a9d3564..48c8c92 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -1289,7 +1289,7 @@ static void rt6_dst_from_metrics_check(struct rt6_info *rt)
 
 static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
 {
-	u32 rt_cookie;
+	u32 rt_cookie = 0;
 
 	if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie)
 		return NULL;

-- 
2.7.4

On Fri, Aug 25, 2017 at 09:05:42AM +0200, Steffen Klassert wrote:

The compiler warning seems to be a false positive, as
rt_cookie != cookie is only checked if rt6_get_cookie_safe
returns true in which case rt_cookie is initialized.

Please disregard this patch.

On Fri, 25 Aug 2017 09:52:17 +0200
Steffen Klassert [off-list ref] wrote:

On Fri, Aug 25, 2017 at 09:05:42AM +0200, Steffen Klassert wrote:

quoted

rt_cookie might be used uninitialized, fix this by
initializing it.

Fixes: c5cff8561d2d ("ipv6: add rcu grace period before freeing fib6_node")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index a9d3564..48c8c92 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -1289,7 +1289,7 @@ static void rt6_dst_from_metrics_check(struct rt6_info *rt)
 
 static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
 {
-	u32 rt_cookie;
+	u32 rt_cookie = 0;
 
 	if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie)
 		return NULL;  

The compiler warning seems to be a false positive, as
rt_cookie != cookie is only checked if rt6_get_cookie_safe
returns true in which case rt_cookie is initialized.

Please disregard this patch.

...or not? I was thinking of sending a similar patch with
uninitialized_var(rt_cookie), but it seems we have similar cases
where we just initialize to zero instead.

I wonder which approach is considered the most acceptable nowadays. I
would be in favour of uninitialized_var() as it doesn't change the
binary output, but https://lwn.net/Articles/529954/ also contains some
valid criticism. Ideas?

From: Stefano Brivio <redacted>
Date: Fri, 25 Aug 2017 11:02:06 +0200

On Fri, 25 Aug 2017 09:52:17 +0200
Steffen Klassert [off-list ref] wrote:

quoted

On Fri, Aug 25, 2017 at 09:05:42AM +0200, Steffen Klassert wrote:

quoted

rt_cookie might be used uninitialized, fix this by
initializing it.

Fixes: c5cff8561d2d ("ipv6: add rcu grace period before freeing fib6_node")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
---
 net/ipv6/route.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/route.c b/net/ipv6/route.c
index a9d3564..48c8c92 100644
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c

@@ -1289,7 +1289,7 @@ static void rt6_dst_from_metrics_check(struct rt6_info *rt)
 
 static struct dst_entry *rt6_check(struct rt6_info *rt, u32 cookie)
 {
-	u32 rt_cookie;
+	u32 rt_cookie = 0;
 
 	if (!rt6_get_cookie_safe(rt, &rt_cookie) || rt_cookie != cookie)
 		return NULL;  

The compiler warning seems to be a false positive, as
rt_cookie != cookie is only checked if rt6_get_cookie_safe
returns true in which case rt_cookie is initialized.

Please disregard this patch.

...or not? I was thinking of sending a similar patch with
uninitialized_var(rt_cookie), but it seems we have similar cases
where we just initialize to zero instead.

I wonder which approach is considered the most acceptable nowadays. I
would be in favour of uninitialized_var() as it doesn't change the
binary output, but https://lwn.net/Articles/529954/ also contains some
valid criticism. Ideas?

Generally speaking I guess initializing to zero is Ok to do.

As far as which approach is better, I don't have any strong opinion.

So I will probably just apply Steffen's patch.

From: Steffen Klassert <steffen.klassert@secunet.com>
Date: Fri, 25 Aug 2017 09:05:42 +0200

rt_cookie might be used uninitialized, fix this by
initializing it.

Fixes: c5cff8561d2d ("ipv6: add rcu grace period before freeing fib6_node")
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>

Applied, thanks.