From: "Arnd Bergmann" <arnd@arndb.de>
To: "Thomas Weißschuh" <linux@weissschuh.net>,
"David S . Miller" <davem@davemloft.net>,
"Eric Dumazet" <edumazet@google.com>,
"Jakub Kicinski" <kuba@kernel.org>,
"Paolo Abeni" <pabeni@redhat.com>,
"Simon Horman" <horms@kernel.org>
Cc: Netdev <netdev@vger.kernel.org>,
linux-kernel@vger.kernel.org, "kernel test robot" <lkp@intel.com>,
stable@vger.kernel.org
Subject: Re: [PATCH] net: avoid build bug in skb extension length calculation
Date: Mon, 18 Dec 2023 20:12:07 +0000 [thread overview]
Message-ID: <0877a767-dea5-4c49-8125-d1995ef55407@app.fastmail.com> (raw)
In-Reply-To: <20231218-net-skbuff-build-bug-v1-1-eefc2fb0a7d3@weissschuh.net>
On Mon, Dec 18, 2023, at 17:06, Thomas Weißschuh wrote:
> GCC seems to incorrectly fail to evaluate skb_ext_total_length() at
> compile time under certain conditions.
>
> The issue even occurs if all values in skb_ext_type_len[] are "0",
> ruling out the possibility of an actual overflow.
>
> As the patch has been in mainline since v6.6 without triggering the
> problem it seems to be a very uncommon occurrence.
>
> As the issue only occurs when -fno-tree-loop-im is specified as part of
> CFLAGS_GCOV, disable the BUILD_BUG_ON() only when building with coverage
> reporting enabled.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Closes:
> https://lore.kernel.org/oe-kbuild-all/202312171924.4FozI5FG-lkp@intel.com/
> Suggested-by: Arnd Bergmann <arnd@arndb.de>
> Link:
> https://lore.kernel.org/lkml/487cfd35-fe68-416f-9bfd-6bb417f98304@app.fastmail.com/
> Fixes: 5d21d0a65b57 ("net: generalize calculation of skb extensions
> length")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Acked-by: Arnd Bergmann <arnd@arndb.de>
> ---
> net/core/skbuff.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/net/core/skbuff.c b/net/core/skbuff.c
> index 83af8aaeb893..94cc40a6f797 100644
> --- a/net/core/skbuff.c
> +++ b/net/core/skbuff.c
> @@ -4825,7 +4825,9 @@ static __always_inline unsigned int
> skb_ext_total_length(void)
> static void skb_extensions_init(void)
> {
> BUILD_BUG_ON(SKB_EXT_NUM >= 8);
> +#if !IS_ENABLED(CONFIG_KCOV_INSTRUMENT_ALL)
> BUILD_BUG_ON(skb_ext_total_length() > 255);
> +#endif
The way I would write this is
BUILD_BUG_ON(!IS_ENABLED(CONFIG_KCOV_INSTRUMENT_ALL) &&
skb_ext_total_length() > 255);
but of course the effect is the same.
Arnd
next prev parent reply other threads:[~2023-12-18 20:12 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-18 17:06 [PATCH] net: avoid build bug in skb extension length calculation Thomas Weißschuh
2023-12-18 20:12 ` Arnd Bergmann [this message]
2023-12-21 7:40 ` patchwork-bot+netdevbpf
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