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 <[email protected]>
---
.../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
Hello:
This patch was applied to netdev/net-next.git (refs/heads/master):
On Thu, 3 Jun 2021 10:34:10 -0700 you wrote:
> 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.
>
> [...]
Here is the summary with links:
- [net-next] net: ethernet: rmnet: Restructure if checks to avoid uninitialized warning
https://git.kernel.org/netdev/net-next/c/118de6106735
You are awesome, thank you!
--
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html
On 2021-06-03 16:40, [email protected] wrote:
> Hello:
>
> This patch was applied to netdev/net-next.git (refs/heads/master):
>
> On Thu, 3 Jun 2021 10:34:10 -0700 you wrote:
>> 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.
>>
>> [...]
>
> Here is the summary with links:
> - [net-next] net: ethernet: rmnet: Restructure if checks to avoid
> uninitialized warning
> https://git.kernel.org/netdev/net-next/c/118de6106735
>
> You are awesome, thank you!
> --
> Deet-doot-dot, I am a bot.
> https://korg.docs.kernel.org/patchwork/pwbot.html
Hi Nathan
Can you tell why CLANG detected this error.
Does it require a bug fix.
Hi Subash,
On 6/3/2021 10:15 PM, [email protected] wrote:
> On 2021-06-03 16:40, [email protected] wrote:
>> Hello:
>>
>> This patch was applied to netdev/net-next.git (refs/heads/master):
>>
>> On Thu, 3 Jun 2021 10:34:10 -0700 you wrote:
>>> 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.
>>>
>>> [...]
>>
>> Here is the summary with links:
>> - [net-next] net: ethernet: rmnet: Restructure if checks to avoid
>> uninitialized warning
>> https://git.kernel.org/netdev/net-next/c/118de6106735
>>
>> You are awesome, thank you!
>> --
>> Deet-doot-dot, I am a bot.
>> https://korg.docs.kernel.org/patchwork/pwbot.html
>
> Hi Nathan
>
> Can you tell why CLANG detected this error.
> Does it require a bug fix.
As far as I understand it, clang does not remember the conditions of
previous if statements when generating this warning. Basically:
void bar(int x)
{
}
int foo(int a, int b)
{
int x;
if (!a && !b)
goto out;
if (a)
x = 1;
else if (b)
x = 2;
bar(x);
out:
return 0;
}
clang will warn that x is uninitialized when neither of the second if
statement's conditions are true, even though we as humans know that is
not possible due to the first if statement. I am guessing this has
something to do with how clang generates its control flow graphs. While
this is a false positive, I do not personally see this as a bug in the
compiler. The code is more clear to both the compiler and humans if it
is written as:
if (a)
x = 1;
else if (b)
x = 2;
else
goto out;
Cheers,
Nathan