[PATCH] netfilter: nf_flow_table_offload: Don't use offset uninitialized in flow_offload_port_{d,s}nat

[Nathan Chancellor]

Clang warns (trimmed the second warning for brevity):

../net/netfilter/nf_flow_table_offload.c:342:2: warning: variable
'offset' is used uninitialized whenever switch default is taken
[-Wsometimes-uninitialized]
default:
^~~~~~~
../net/netfilter/nf_flow_table_offload.c:346:57: note: uninitialized use
occurs here
flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
^~~~~~
../net/netfilter/nf_flow_table_offload.c:331:12: note: initialize the
variable 'offset' to silence this warning
u32 offset;
^
= 0

Match what was done in the flow_offload_ipv{4,6}_{d,s}nat functions and
just return in the default case, since port would also be uninitialized.

Fixes: c29f74e0df7a ("netfilter: nf_flow_table: hardware offload support")
Link: https://github.com/ClangBuiltLinux/linux/issues/780
Signed-off-by: Nathan Chancellor <natecha...@gmail.com>
---
net/netfilter/nf_flow_table_offload.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/netfilter/nf_flow_table_offload.c b/net/netfilter/nf_flow_table_offload.c
index c54c9a6cc981..a77a6e1cfd64 100644
--- a/net/netfilter/nf_flow_table_offload.c
+++ b/net/netfilter/nf_flow_table_offload.c
@@ -340,7 +340,7 @@ static void flow_offload_port_snat(struct net *net,
offset = 0; /* offsetof(struct tcphdr, dest); */
break;
default:
- break;
+ return;
}

flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
@@ -367,7 +367,7 @@ static void flow_offload_port_dnat(struct net *net,
offset = 0; /* offsetof(struct tcphdr, dest); */
break;
default:
- break;
+ return;
}

flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
--
2.24.0

[Nick Desaulniers]

On Tue, Nov 26, 2019 at 12:13 PM Nathan Chancellor
<natecha...@gmail.com> wrote:
>
> Clang warns (trimmed the second warning for brevity):
>
> ../net/netfilter/nf_flow_table_offload.c:342:2: warning: variable
> 'offset' is used uninitialized whenever switch default is taken
> [-Wsometimes-uninitialized]
> default:
> ^~~~~~~
> ../net/netfilter/nf_flow_table_offload.c:346:57: note: uninitialized use
> occurs here
> flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
> ^~~~~~
> ../net/netfilter/nf_flow_table_offload.c:331:12: note: initialize the
> variable 'offset' to silence this warning
> u32 offset;
> ^
> = 0
>
> Match what was done in the flow_offload_ipv{4,6}_{d,s}nat functions and
> just return in the default case, since port would also be uninitialized.

Thanks for the patch. I have a report of this from kernelci bot, would
you mind crediting it:
Reported-by: kernelci.org bot <b...@kernelci.org>
Looks like `port` is uninitialized (prior to your patch), too.
Reviewed-by: Nick Desaulniers <ndesau...@google.com>
These two functions look identical except for the mask. The
maintainers should consider reusing more code between them and passing
in the mask.

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--
Thanks,
~Nick Desaulniers

[Pablo Neira Ayuso]

On Tue, Nov 26, 2019 at 01:12:26PM -0700, Nathan Chancellor wrote:
> Clang warns (trimmed the second warning for brevity):
>
> ../net/netfilter/nf_flow_table_offload.c:342:2: warning: variable
> 'offset' is used uninitialized whenever switch default is taken
> [-Wsometimes-uninitialized]
> default:
> ^~~~~~~
> ../net/netfilter/nf_flow_table_offload.c:346:57: note: uninitialized use
> occurs here
> flow_offload_mangle(entry, flow_offload_l4proto(flow), offset,
> ^~~~~~
> ../net/netfilter/nf_flow_table_offload.c:331:12: note: initialize the
> variable 'offset' to silence this warning
> u32 offset;
> ^
> = 0
>
> Match what was done in the flow_offload_ipv{4,6}_{d,s}nat functions and
> just return in the default case, since port would also be uninitialized.

Applied, thanks.