Commit d6e5794b authored by Thomas Weißschuh's avatar Thomas Weißschuh Committed by Paolo Abeni
Browse files

net: avoid build bug in skb extension length calculation 



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: default avatarkernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202312171924.4FozI5FG-lkp@intel.com/


Suggested-by: default avatarArnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/lkml/487cfd35-fe68-416f-9bfd-6bb417f98304@app.fastmail.com/


Fixes: 5d21d0a6 ("net: generalize calculation of skb extensions length")
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarThomas Weißschuh <linux@weissschuh.net>
Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20231218-net-skbuff-build-bug-v1-1-eefc2fb0a7d3@weissschuh.net


Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 7cb8cd4d

net/core/skbuff.c

+2 −0
Original line number Diff line number Diff line
@@ -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(),