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net: avoid build bug in skb extension length calculation

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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: 5d21d0a65b ("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>
Link: https://lore.kernel.org/r/20231218-net-skbuff-build-bug-v1-1-eefc2fb0a7d3@weissschuh.net
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
This commit is contained in:
Thomas Weißschuh 2023-12-18 18:06:54 +01:00 committed by Paolo Abeni
parent 7cb8cd4daa
commit d6e5794b06
1 changed files with 2 additions and 0 deletions
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2
net/core/skbuff.c
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@ -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(),