linux-kernel - [PATCH] selinux: reject invalid ebitmaps

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Date:   Fri, 18 Aug 2023 17:29:09 +0200
From:   Christian Göttsche <cgzones@...glemail.com>
To:     selinux@...r.kernel.org
Cc:     Paul Moore <paul@...l-moore.com>,
        Stephen Smalley <stephen.smalley.work@...il.com>,
        Eric Paris <eparis@...isplace.org>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] selinux: reject invalid ebitmaps

Reject ebitmaps with a node containing an empty map or with an incorrect
highbit.  Both checks are already performed by userspace, the former
since 2008 (patch 13cd4c896068 ("initial import from svn trunk revision
2950")), the latter since v2.7 in 2017 (patch 75b14a5de10a ("libsepol:
ebitmap: reject loading bitmaps with incorrect high bit")).

Signed-off-by: Christian Göttsche <cgzones@...glemail.com>
---
 security/selinux/ss/ebitmap.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/security/selinux/ss/ebitmap.c b/security/selinux/ss/ebitmap.c
index 77875ad355f7..ac9da819531d 100644
--- a/security/selinux/ss/ebitmap.c
+++ b/security/selinux/ss/ebitmap.c
@@ -450,6 +450,10 @@ int ebitmap_read(struct ebitmap *e, void *fp)
 			goto bad;
 		}
 		map = le64_to_cpu(mapbits);
+		if (!map) {
+			pr_err("SELinux: ebitmap: empty map\n");
+			goto bad;
+		}
 
 		index = (startbit - n->startbit) / EBITMAP_UNIT_SIZE;
 		while (map) {
@@ -457,6 +461,13 @@ int ebitmap_read(struct ebitmap *e, void *fp)
 			map = EBITMAP_SHIFT_UNIT_SIZE(map);
 		}
 	}
+
+	if (n && n->startbit + EBITMAP_SIZE != e->highbit) {
+		pr_err("SELinux: ebitmap: high bit %d has not the expected value %ld\n",
+		       e->highbit, n->startbit + EBITMAP_SIZE);
+		goto bad;
+	}
+
 ok:
 	rc = 0;
 out:
-- 
2.40.1