From: Andrey Ryabinin aryabinin@virtuozzo.com

commit 68920c973254c5b71a684645c5f6f82d6732c5d6 upstream.

With upcoming CONFIG_UBSAN the following BUILD_BUG_ON in net/mac80211/debugfs.c starts to trigger:

BUILD_BUG_ON(hw_flag_names[NUM_IEEE80211_HW_FLAGS] != (void *)0x1);

It seems, that compiler instrumentation causes some code deoptimizations. Because of that GCC is not being able to resolve condition in BUILD_BUG_ON() at compile time.

We could make size of hw_flag_names array unspecified and replace the condition in BUILD_BUG_ON() with following:

ARRAY_SIZE(hw_flag_names) != NUM_IEEE80211_HW_FLAGS

That will have the same effect as before (adding new flag without updating array will trigger build failure) except it doesn't fail with CONFIG_UBSAN. As a bonus this patch slightly decreases size of hw_flag_names array.

Signed-off-by: Andrey Ryabinin aryabinin@virtuozzo.com Cc: Johannes Berg johannes@sipsolutions.net Cc: "David S. Miller" davem@davemloft.net Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org [Daniel: backport to 4.4.] Signed-off-by: Daniel Wagner daniel.wagner@siemens.com ---

Hi,

The only stable tree which is missing this fix is 4.4. 4.1 doesn't have 30686bf7f5b3 ("mac80211: convert HW flags to unsigned long bitmap") which makes gcc unhappy with allmodconfig. 4.9 contains the fix.

Thanks, Daniel

net/mac80211/debugfs.c | 7 ++----- 1 file changed, 2 insertions(+), 5 deletions(-)

diff --git a/net/mac80211/debugfs.c b/net/mac80211/debugfs.c index 4d2aaebd4f97..e546a987a9d3 100644 --- a/net/mac80211/debugfs.c +++ b/net/mac80211/debugfs.c @@ -91,7 +91,7 @@ static const struct file_operations reset_ops = { }; #endif

-static const char *hw_flag_names[NUM_IEEE80211_HW_FLAGS + 1] = { +static const char *hw_flag_names[] = { #define FLAG(F) [IEEE80211_HW_##F] = #F FLAG(HAS_RATE_CONTROL), FLAG(RX_INCLUDES_FCS), @@ -125,9 +125,6 @@ static const char *hw_flag_names[NUM_IEEE80211_HW_FLAGS + 1] = { FLAG(TDLS_WIDER_BW), FLAG(SUPPORTS_AMSDU_IN_AMPDU), FLAG(BEACON_TX_STATUS), - - /* keep last for the build bug below */ - (void *)0x1 #undef FLAG };

@@ -147,7 +144,7 @@ static ssize_t hwflags_read(struct file *file, char __user *user_buf, /* fail compilation if somebody adds or removes * a flag without updating the name array above */ - BUILD_BUG_ON(hw_flag_names[NUM_IEEE80211_HW_FLAGS] != (void *)0x1); + BUILD_BUG_ON(ARRAY_SIZE(hw_flag_names) != NUM_IEEE80211_HW_FLAGS);

for (i = 0; i < NUM_IEEE80211_HW_FLAGS; i++) { if (test_bit(i, local->hw.flags))