[PATCH] scripts/sorttable: Fix orc_sort_cmp() to maintain symmetry and transitivity

[Kuan-Wei Chiu]

The orc_sort_cmp() function, used with qsort(), previously violated the
symmetry and transitivity rules required by the C standard.
Specifically, when both entries are ORC_TYPE_UNDEFINED, it could result
in both a < b and b < a, which breaks the required symmetry and
transitivity. This can lead to undefined behavior and incorrect sorting
results, potentially causing memory corruption in glibc
implementations [1].

Symmetry: If x < y, then y > x.
Transitivity: If x < y and y < z, then x < z.

Fix the comparison logic to return 0 when both entries are
ORC_TYPE_UNDEFINED, ensuring compliance with qsort() requirements.

Link: https://www.qualys.com/2024/01/30/qsort.txt [1]
Fixes: 57fa18994285 ("scripts/sorttable: Implement build-time ORC unwind table sorting")
Fixes: fb799447ae29 ("x86,objtool: Split UNWIND_HINT_EMPTY in two")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Kuan-Wei Chiu <visitorckw@xxxxxxxxx>
---
 scripts/sorttable.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/scripts/sorttable.h b/scripts/sorttable.h
index 7bd0184380d3..a7c5445baf00 100644
--- a/scripts/sorttable.h
+++ b/scripts/sorttable.h
@@ -110,7 +110,7 @@ static inline unsigned long orc_ip(const int *ip)
 
 static int orc_sort_cmp(const void *_a, const void *_b)
 {
-	struct orc_entry *orc_a;
+	struct orc_entry *orc_a, *orc_b;
 	const int *a = g_orc_ip_table + *(int *)_a;
 	const int *b = g_orc_ip_table + *(int *)_b;
 	unsigned long a_val = orc_ip(a);
@@ -128,6 +128,9 @@ static int orc_sort_cmp(const void *_a, const void *_b)
 	 * whitelisted .o files which didn't get objtool generation.
 	 */
 	orc_a = g_orc_table + (a - g_orc_ip_table);
+	orc_b = g_orc_table + (b - g_orc_ip_table);
+	if (orc_a->type == ORC_TYPE_UNDEFINED && orc_b->type == ORC_TYPE_UNDEFINED)
+		return 0;
 	return orc_a->type == ORC_TYPE_UNDEFINED ? -1 : 1;
 }
 
-- 
2.34.1