| Message ID | 20231218-net-skbuff-build-bug-v1-1-eefc2fb0a7d3@weissschuh.net (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d6e5794b06c0fab74fe6e4fa55d508a5ceb14735 |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: avoid build bug in skb extension length calculation | expand |
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@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> Acked-by: Arnd Bergmann <arnd@arndb.de> > --- > 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
Hello: This patch was applied to netdev/net.git (main) by Paolo Abeni <pabeni@redhat.com>: On Mon, 18 Dec 2023 18:06:54 +0100 you 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. > > [...] Here is the summary with links: - net: avoid build bug in skb extension length calculation https://git.kernel.org/netdev/net/c/d6e5794b06c0 You are awesome, thank you!
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(),
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(+) --- base-commit: ceb6a6f023fd3e8b07761ed900352ef574010bcb change-id: 20231218-net-skbuff-build-bug-4a7c1103d0a6 Best regards,