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@xxxxxxxxx> Closes: https://lore.kernel.org/oe-kbuild-all/202312171924.4FozI5FG-lkp@xxxxxxxxx/ Suggested-by: Arnd Bergmann <arnd@xxxxxxxx> Link: https://lore.kernel.org/lkml/487cfd35-fe68-416f-9bfd-6bb417f98304@xxxxxxxxxxxxxxxx/ Fixes: 5d21d0a65b57 ("net: generalize calculation of skb extensions length") Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Thomas Weißschuh <linux@xxxxxxxxxxxxxx> --- 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@xxxxxxxxxxxxxx>
