linux-kernel - [PATCH 5.15 270/279] selinux: fix NULL-pointer dereference when hashtab allocation fails

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Message-Id: <20211124115728.017444288@linuxfoundation.org>
Date:   Wed, 24 Nov 2021 12:59:17 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Ondrej Mosnacek <omosnace@...hat.com>,
        Paul Moore <paul@...l-moore.com>
Subject: [PATCH 5.15 270/279] selinux: fix NULL-pointer dereference when hashtab allocation fails

From: Ondrej Mosnacek <omosnace@...hat.com>

commit dc27f3c5d10c58069672215787a96b4fae01818b upstream.

When the hash table slot array allocation fails in hashtab_init(),
h->size is left initialized with a non-zero value, but the h->htable
pointer is NULL. This may then cause a NULL pointer dereference, since
the policydb code relies on the assumption that even after a failed
hashtab_init(), hashtab_map() and hashtab_destroy() can be safely called
on it. Yet, these detect an empty hashtab only by looking at the size.

Fix this by making sure that hashtab_init() always leaves behind a valid
empty hashtab when the allocation fails.

Cc: stable@...r.kernel.org
Fixes: 03414a49ad5f ("selinux: do not allocate hashtabs dynamically")
Signed-off-by: Ondrej Mosnacek <omosnace@...hat.com>
Signed-off-by: Paul Moore <paul@...l-moore.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 security/selinux/ss/hashtab.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

--- a/security/selinux/ss/hashtab.c
+++ b/security/selinux/ss/hashtab.c
@@ -30,13 +30,20 @@ static u32 hashtab_compute_size(u32 nel)
 
 int hashtab_init(struct hashtab *h, u32 nel_hint)
 {
-	h->size = hashtab_compute_size(nel_hint);
+	u32 size = hashtab_compute_size(nel_hint);
+
+	/* should already be zeroed, but better be safe */
 	h->nel = 0;
-	if (!h->size)
-		return 0;
+	h->size = 0;
+	h->htable = NULL;
 
-	h->htable = kcalloc(h->size, sizeof(*h->htable), GFP_KERNEL);
-	return h->htable ? 0 : -ENOMEM;
+	if (size) {
+		h->htable = kcalloc(size, sizeof(*h->htable), GFP_KERNEL);
+		if (!h->htable)
+			return -ENOMEM;
+		h->size = size;
+	}
+	return 0;
 }
 
 int __hashtab_insert(struct hashtab *h, struct hashtab_node **dst,