[PATCH] net: avoid uninitialized variable

From: zhong jiang <redacted>

when I compiler the newest kernel, I hit the following error with
Werror=may-uninitalized.

net/core/flow_dissector.c: In function ?._skb_flow_dissect?
include/uapi/linux/swab.h:100:46: error: ?.lan?.may be used uninitialized in this function [-Werror=maybe-uninitialized]
net/core/flow_dissector.c:248:26: note: ?.lan?.was declared here

This adds an additional check for proto to explicitly tell the compiler
that vlan pointer have the correct value before it is used.

Signed-off-by: zhong jiang <redacted>
---
 net/core/flow_dissector.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 1a7b80f..a04d9cf 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c

@@ -245,7 +245,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 	}
 	case htons(ETH_P_8021AD):
 	case htons(ETH_P_8021Q): {
-		const struct vlan_hdr *vlan;
+		const struct vlan_hdr *vlan = NULL;
 
 		if (skb_vlan_tag_present(skb))
 			proto = skb->protocol;

@@ -276,7 +276,8 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
 				key_vlan->vlan_id = skb_vlan_tag_get_id(skb);
 				key_vlan->vlan_priority =
 					(skb_vlan_tag_get_prio(skb) >> VLAN_PRIO_SHIFT);
-			} else {
+			} else if (proto == cpu_to_be16(ETH_P_8021Q) ||
+						proto == cpu_to_be16(ETH_P_8021AD)) {
 				key_vlan->vlan_id = ntohs(vlan->h_vlan_TCI) &
 					VLAN_VID_MASK;
 				key_vlan->vlan_priority =

-- 
1.8.3.1

On Thu, Oct 27, 2016 at 11:56 AM, zhongjiang [off-list ref] wrote:

It seems there is one similar patch already.
You could refer to https://patchwork.kernel.org/patch/9389565/

Regards
Feng

On 2016/10/27 12:02, Gao Feng wrote:

On Thu, Oct 27, 2016 at 11:56 AM, zhongjiang [off-list ref] wrote:

quoted

From: zhong jiang <redacted>

when I compiler the newest kernel, I hit the following error with
Werror=may-uninitalized.

net/core/flow_dissector.c: In function ?._skb_flow_dissect?
include/uapi/linux/swab.h:100:46: error: ?.lan?.may be used uninitialized in this function [-Werror=maybe-uninitialized]
net/core/flow_dissector.c:248:26: note: ?.lan?.was declared here

This adds an additional check for proto to explicitly tell the compiler
that vlan pointer have the correct value before it is used.

Signed-off-by: zhong jiang <redacted>
---
 net/core/flow_dissector.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 1a7b80f..a04d9cf 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c

@@ -245,7 +245,7 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
        }
        case htons(ETH_P_8021AD):
        case htons(ETH_P_8021Q): {
-               const struct vlan_hdr *vlan;
+               const struct vlan_hdr *vlan = NULL;

                if (skb_vlan_tag_present(skb))
                        proto = skb->protocol;

@@ -276,7 +276,8 @@ bool __skb_flow_dissect(const struct sk_buff *skb,
                                key_vlan->vlan_id = skb_vlan_tag_get_id(skb);
                                key_vlan->vlan_priority =
                                        (skb_vlan_tag_get_prio(skb) >> VLAN_PRIO_SHIFT);
-                       } else {
+                       } else if (proto == cpu_to_be16(ETH_P_8021Q) ||
+                                               proto == cpu_to_be16(ETH_P_8021AD)) {
                                key_vlan->vlan_id = ntohs(vlan->h_vlan_TCI) &
                                        VLAN_VID_MASK;
                                key_vlan->vlan_priority =
--

1.8.3.1

It seems there is one similar patch already.
You could refer to https://patchwork.kernel.org/patch/9389565/

Regards
Feng

.

 sorry, I doesn't notice that patch.

 Thanks
 zhongjiang