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SubjectRe: [PATCH] netfilter: xt_TPROXY: fix clang -Wformat warnings:
On Thu, Jul 7, 2022 at 12:18 PM Justin Stitt <justinstitt@google.com> wrote:
>
> When building with Clang we encounter these warnings:
> | net/netfilter/xt_TPROXY.c:173:5: error: format specifies type 'unsigned
> | char' but the argument has type 'int' [-Werror,-Wformat] tproto,
> | &iph->saddr, ntohs(hp->source),
> -
> | net/netfilter/xt_TPROXY.c:181:4: error: format specifies type 'unsigned
> | char' but the argument has type 'int' [-Werror,-Wformat] tproto,
> | &iph->saddr, ntohs(hp->source),
>
> The format specifier `%hhu` refers to a u8 while tproto is an int. In
> this case we weren't losing any data because ipv6_find_hdr returns an
> int but its return value (nexthdr) is a u8. This u8 gets widened to an
> int when returned from ipv6_find_hdr and assigned to tproto. The
> previous format specifier is functionally fine but still produces a
> warning due to a type mismatch.
>
> The fix is simply to listen to Clang and change `%hhu` to `%d` for both
> instances of the warning.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/378
> Signed-off-by: Justin Stitt <justinstitt@google.com>

Thanks for the patch, this fixes the warning I observe when building
ARCH=arm64 allmodconfig with -Wno-format removed!
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> It should be noted that for this entire file to build without -Wformat
> warnings you should apply this `ntohs` patch which fixed many, many
> -Wformat warnings in the kernel.
> https://lore.kernel.org/all/20220608223539.470472-1-justinstitt@google.com/
>
> net/netfilter/xt_TPROXY.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/netfilter/xt_TPROXY.c b/net/netfilter/xt_TPROXY.c
> index 459d0696c91a..5d74abffc94f 100644
> --- a/net/netfilter/xt_TPROXY.c
> +++ b/net/netfilter/xt_TPROXY.c
> @@ -169,7 +169,7 @@ tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
> targets on the same rule yet */
> skb->mark = (skb->mark & ~tgi->mark_mask) ^ tgi->mark_value;
>
> - pr_debug("redirecting: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
> + pr_debug("redirecting: proto %d %pI6:%hu -> %pI6:%hu, mark: %x\n",
> tproto, &iph->saddr, ntohs(hp->source),
> laddr, ntohs(lport), skb->mark);
>
> @@ -177,7 +177,7 @@ tproxy_tg6_v1(struct sk_buff *skb, const struct xt_action_param *par)
> return NF_ACCEPT;
> }
>
> - pr_debug("no socket, dropping: proto %hhu %pI6:%hu -> %pI6:%hu, mark: %x\n",
> + pr_debug("no socket, dropping: proto %d %pI6:%hu -> %pI6:%hu, mark: %x\n",
> tproto, &iph->saddr, ntohs(hp->source),
> &iph->daddr, ntohs(hp->dest), skb->mark);
>
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>


--
Thanks,
~Nick Desaulniers

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