[PATCH net-next] net: ethernet: rmnet: Restructure if checks to avoid uninitialized warning

Nathan Chancellor
2021-06-03T17:34:36Z

Clang warns that proto in rmnet_map_v5_checksum_uplink_packet() might be
used uninitialized:

drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c:283:14: warning:
variable 'proto' is used uninitialized whenever 'if' condition is false
[-Wsometimes-uninitialized]
} else if (skb->protocol == htons(ETH_P_IPV6)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c:295:36: note:
uninitialized use occurs here
check = rmnet_map_get_csum_field(proto, trans);
^~~~~
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c:283:10: note:
remove the 'if' if its condition is always true
} else if (skb->protocol == htons(ETH_P_IPV6)) {
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c:270:11: note:
initialize the variable 'proto' to silence this warning
u8 proto;
^
= '\0'
1 warning generated.

This is technically a false positive because there is an if statement
above this one that checks skb->protocol for not being either
ETH_P_IP{,V6}. However, it is more obvious to sink that into the if
statement as an else branch, which makes the code clearer and fixes the
warning.

At the same time, move the "IS_ENABLED(CONFIG_IPV6)" into the else if
condition so that the else branch of the preprocessor conditional can
be shared, since there is no build failure with CONFIG_IPV6 disabled.

Fixes: b6e5d27e32ef ("net: ethernet: rmnet: Add support for MAPv5 egress packets")
Link: https://github.com/ClangBuiltLinux/linux/issues/1390
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
---
.../net/ethernet/qualcomm/rmnet/rmnet_map_data.c | 13 +++----------
1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
index 6492ec5bdec4..cecf72be5102 100644
--- a/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
+++ b/drivers/net/ethernet/qualcomm/rmnet/rmnet_map_data.c
@@ -269,27 +269,20 @@ static void rmnet_map_v5_checksum_uplink_packet(struct sk_buff *skb,
void *trans;
u8 proto;

- if (skb->protocol != htons(ETH_P_IP) &&
- skb->protocol != htons(ETH_P_IPV6)) {
- priv->stats.csum_err_invalid_ip_version++;
- goto sw_csum;
- }
-
if (skb->protocol == htons(ETH_P_IP)) {
u16 ip_len = ((struct iphdr *)iph)->ihl * 4;

proto = ((struct iphdr *)iph)->protocol;
trans = iph + ip_len;
- } else if (skb->protocol == htons(ETH_P_IPV6)) {
-#if IS_ENABLED(CONFIG_IPV6)
+ } else if (IS_ENABLED(CONFIG_IPV6) &&
+ skb->protocol == htons(ETH_P_IPV6)) {
u16 ip_len = sizeof(struct ipv6hdr);

proto = ((struct ipv6hdr *)iph)->nexthdr;
trans = iph + ip_len;
-#else
+ } else {
priv->stats.csum_err_invalid_ip_version++;
goto sw_csum;
-#endif /* CONFIG_IPV6 */
}

check = rmnet_map_get_csum_field(proto, trans);

base-commit: 270d47dc1fc4756a0158778084a236bc83c156d2
--
2.32.0.rc3