linux-kernel - [PATCH] audit: fix out-of-bounds read in audit_compare_dname

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Message-Id: <20250902110049.4437-1-disclosure@aisle.com>
Date: Tue,  2 Sep 2025 14:00:49 +0300
From: Stanislav Fort <stanislav.fort@...le.com>
To: paul@...l-moore.com,
	audit@...r.kernel.org
Cc: torvalds@...uxfoundation.org,
	eparis@...hat.com,
	security@...nel.org,
	linux-kernel@...r.kernel.org,
	Stanislav Fort <disclosure@...le.com>
Subject: [PATCH] audit: fix out-of-bounds read in audit_compare_dname_path

When a watch on dir=/ is combined with an fsnotify event for a
single-character name directly under / (e.g., creating /a), an
out-of-bounds read can occur in audit_compare_dname_path().

The helper parent_len() returns 1 for "/". In audit_compare_dname_path(),
when parentlen equals the full path length (1), the code sets p = path + 1
and pathlen = 1 - 1 = 0. The subsequent loop then dereferences
p[pathlen - 1] (i.e., p[-1]), causing an out-of-bounds read.

Fix this by adding a pathlen > 0 check to the while loop condition
to prevent the out-of-bounds access.

Reported-by: Stanislav Fort <disclosure@...le.com>
Suggested-by: Linus Torvalds <torvalds@...uxfoundation.org>
Signed-off-by: Stanislav Fort <disclosure@...le.com>
---
 kernel/auditfilter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/auditfilter.c b/kernel/auditfilter.c
index e3f42018ed46..f7708fe2c457 100644
--- a/kernel/auditfilter.c
+++ b/kernel/auditfilter.c
@@ -1326,7 +1326,7 @@ int audit_compare_dname_path(const struct qstr *dname, const char *path, int par
 
 	/* handle trailing slashes */
 	pathlen -= parentlen;
-	while (p[pathlen - 1] == '/')
+	while (pathlen > 0 && p[pathlen - 1] == '/')
 		pathlen--;
 
 	if (pathlen != dlen)
-- 
2.39.3 (Apple Git-146)