Patch "net/mac80211/debugfs.c: prevent build failure with CONFIG_UBSAN=y" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

net/mac80211/debugfs.c: prevent build failure with CONFIG_UBSAN=y

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
net-mac80211-debugfs.c-prevent-build-failure-with-config_ubsan-y.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrey Ryabinin <[email protected]>
Date: Wed, 20 Jan 2016 15:00:51 -0800
Subject: net/mac80211/debugfs.c: prevent build failure with CONFIG_UBSAN=y

From: Andrey Ryabinin <[email protected]>

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.

---

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(-)

@@ -91,7 +91,7 @@ static const struct file_operations rese
 };
 #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_IEE
 	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
 	/* 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))

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/net-mac80211-debugfs.c-prevent-build-failure-with-config_ubsan-y.patch