UPSTREAM: bug: switch data corruption check to __must_check

(cherry-picked from 85caa95b9f19bb3a26d7e025d1134760b69e0c40)

The CHECK_DATA_CORRUPTION() macro was designed to have callers do
something meaningful/protective on failure.  However, using "return
false" in the macro too strictly limits the design patterns of callers.
Instead, let callers handle the logic test directly, but make sure that
the result IS checked by forcing __must_check (which appears to not be
able to be used directly on macro expressions).

Change-Id: I212eaf9cff926d6f4c04f84d438cd121bda82c2c
Link: http://lkml.kernel.org/r/20170206204547.GA125312@beast
Signed-off-by: Kees Cook <keescook@chromium.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Satya Tangirala <satyat@google.com>
Signed-off-by: khusika <khusikadhamar@gmail.com>

include/linux/bug.h

@@ -47,18 +47,20 @@ static inline enum bug_trap_type report_bug(unsigned long bug_addr,
 
 /*
  * Since detected data corruption should stop operation on the affected
- * structures, this returns false if the corruption condition is found.
+ * structures. Return value must be checked and sanely acted on by caller.
  */
+static inline __must_check bool check_data_corruption(bool v) { return v; }
 #define CHECK_DATA_CORRUPTION(condition, fmt, ...)			 \
-	do {								 \
-		if (unlikely(condition)) {				 \
+	check_data_corruption(({					 \
+		bool corruption = unlikely(condition);			 \
+		if (corruption) {					 \
 			if (IS_ENABLED(CONFIG_BUG_ON_DATA_CORRUPTION)) { \
 				pr_err(fmt, ##__VA_ARGS__);		 \
 				BUG();					 \
 			} else						 \
 				WARN(1, fmt, ##__VA_ARGS__);		 \
-			return false;					 \
 		}							 \
-	} while (0)
+		corruption;						 \
+	}))
 
 #endif	/* _LINUX_BUG_H */

lib/list_debug.c

@@ -20,15 +20,16 @@
 bool __list_add_valid(struct list_head *new, struct list_head *prev,
 		      struct list_head *next)
 {
-	CHECK_DATA_CORRUPTION(next->prev != prev,
-		"list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
-		prev, next->prev, next);
-	CHECK_DATA_CORRUPTION(prev->next != next,
-		"list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
-		next, prev->next, prev);
-	CHECK_DATA_CORRUPTION(new == prev || new == next,
-		"list_add double add: new=%p, prev=%p, next=%p.\n",
-		new, prev, next);
+	if (CHECK_DATA_CORRUPTION(next->prev != prev,
+			"list_add corruption. next->prev should be prev (%p), but was %p. (next=%p).\n",
+			prev, next->prev, next) ||
+	    CHECK_DATA_CORRUPTION(prev->next != next,
+			"list_add corruption. prev->next should be next (%p), but was %p. (prev=%p).\n",
+			next, prev->next, prev) ||
+	    CHECK_DATA_CORRUPTION(new == prev || new == next,
+			"list_add double add: new=%p, prev=%p, next=%p.\n",
+			new, prev, next))
+		return false;
 
 	return true;
 }
@@ -41,18 +42,20 @@ bool __list_del_entry_valid(struct list_head *entry)
 	prev = entry->prev;
 	next = entry->next;
 
-	CHECK_DATA_CORRUPTION(next == LIST_POISON1,
-		"list_del corruption, %p->next is LIST_POISON1 (%p)\n",
-		entry, LIST_POISON1);
-	CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
-		"list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
-		entry, LIST_POISON2);
-	CHECK_DATA_CORRUPTION(prev->next != entry,
-		"list_del corruption. prev->next should be %p, but was %p\n",
-		entry, prev->next);
-	CHECK_DATA_CORRUPTION(next->prev != entry,
-		"list_del corruption. next->prev should be %p, but was %p\n",
-		entry, next->prev);
+	if (CHECK_DATA_CORRUPTION(next == LIST_POISON1,
+			"list_del corruption, %p->next is LIST_POISON1 (%p)\n",
+			entry, LIST_POISON1) ||
+	    CHECK_DATA_CORRUPTION(prev == LIST_POISON2,
+			"list_del corruption, %p->prev is LIST_POISON2 (%p)\n",
+			entry, LIST_POISON2) ||
+	    CHECK_DATA_CORRUPTION(prev->next != entry,
+			"list_del corruption. prev->next should be %p, but was %p\n",
+			entry, prev->next) ||
+	    CHECK_DATA_CORRUPTION(next->prev != entry,
+			"list_del corruption. next->prev should be %p, but was %p\n",
+			entry, next->prev))
+		return false;
+
 	return true;
 
 }