From: "Thomas Weißschuh" <linux@weissschuh.net>
To: "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@vger.kernel.org, linux-kernel@vger.kernel.org,
"kernel test robot" <lkp@intel.com>,
"Arnd Bergmann" <arnd@arndb.de>,
stable@vger.kernel.org, "Thomas Weißschuh" <linux@weissschuh.net>
Subject: [PATCH] net: avoid build bug in skb extension length calculation
Date: Mon, 18 Dec 2023 18:06:54 +0100 [thread overview]
Message-ID: <20231218-net-skbuff-build-bug-v1-1-eefc2fb0a7d3@weissschuh.net> (raw)
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>
---
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
skbuff_ext_cache = kmem_cache_create("skbuff_ext_cache",
SKB_EXT_ALIGN_VALUE * skb_ext_total_length(),
---
base-commit: ceb6a6f023fd3e8b07761ed900352ef574010bcb
change-id: 20231218-net-skbuff-build-bug-4a7c1103d0a6
Best regards,
--
Thomas Weißschuh <linux@weissschuh.net>
next reply other threads:[~2023-12-18 17:07 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-18 17:06 Thomas Weißschuh [this message]
2023-12-18 20:12 ` [PATCH] net: avoid build bug in skb extension length calculation Arnd Bergmann
2023-12-21 7:40 ` patchwork-bot+netdevbpf
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