[PATCH mm v3 33/34] kasan: better identify bug types for tag-based modes

[andrey . konovalov]

From: Andrey Konovalov <andreyknvl@xxxxxxxxxx>

Identify the bug type for the tag-based modes based on the stack trace
entries found in the stack ring.

If a free entry is found first (meaning that it was added last), mark the
bug as use-after-free. If an alloc entry is found first, mark the bug as
slab-out-of-bounds. Otherwise, assign the common bug type.

This change returns the functionalify of the previously dropped
CONFIG_KASAN_TAGS_IDENTIFY.

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>
Signed-off-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
---
 mm/kasan/report_tags.c | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/mm/kasan/report_tags.c b/mm/kasan/report_tags.c
index 57f7355377f1..d3510424d29b 100644
--- a/mm/kasan/report_tags.c
+++ b/mm/kasan/report_tags.c
@@ -10,7 +10,7 @@
 
 extern struct kasan_stack_ring stack_ring;
 
-static const char *get_bug_type(struct kasan_report_info *info)
+static const char *get_common_bug_type(struct kasan_report_info *info)
 {
 	/*
 	 * If access_size is a negative number, then it has reason to be
@@ -37,9 +37,8 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
 	bool is_free;
 	bool alloc_found = false, free_found = false;
 
-	info->bug_type = get_bug_type(info);
-
-	if (!info->cache || !info->object)
+	if (!info->cache || !info->object) {
+		info->bug_type = get_common_bug_type(info);
 		return;
 	}
 
@@ -84,6 +83,13 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
 			info->free_track.pid = pid;
 			info->free_track.stack = stack;
 			free_found = true;
+
+			/*
+			 * If a free entry is found first, the bug is likely
+			 * a use-after-free.
+			 */
+			if (!info->bug_type)
+				info->bug_type = "use-after-free";
 		} else {
 			/* Second alloc of the same object. Give up. */
 			if (alloc_found)
@@ -92,8 +98,19 @@ void kasan_complete_mode_report_info(struct kasan_report_info *info)
 			info->alloc_track.pid = pid;
 			info->alloc_track.stack = stack;
 			alloc_found = true;
+
+			/*
+			 * If an alloc entry is found first, the bug is likely
+			 * an out-of-bounds.
+			 */
+			if (!info->bug_type)
+				info->bug_type = "slab-out-of-bounds";
 		}
 	}
 
 	write_unlock_irqrestore(&stack_ring.lock, flags);
+
+	/* Assign the common bug type if no entries were found. */
+	if (!info->bug_type)
+		info->bug_type = get_common_bug_type(info);
 }
-- 
2.25.1