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@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> Acked-by: Arnd Bergmann <arnd@xxxxxxxx> > --- > 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
