linux-kernel - [PATCH 3.16 092/204] lsm: fix smack_inode_removexattr and xattr

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Message-ID: <lsq.1514480744.257484541@decadent.org.uk>
Date:   Thu, 28 Dec 2017 17:05:44 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org,
        "James Morris" <james.l.morris@...cle.com>,
        "Konstantin Khlebnikov" <khlebnikov@...dex-team.ru>,
        "Casey Schaufler" <casey@...aufler-ca.com>
Subject: [PATCH 3.16 092/204] lsm: fix smack_inode_removexattr and
 xattr_getsecurity memleak

3.16.52-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Casey Schaufler <casey@...aufler-ca.com>

commit 57e7ba04d422c3d41c8426380303ec9b7533ded9 upstream.

security_inode_getsecurity() provides the text string value
of a security attribute. It does not provide a "secctx".
The code in xattr_getsecurity() that calls security_inode_getsecurity()
and then calls security_release_secctx() happened to work because
SElinux and Smack treat the attribute and the secctx the same way.
It fails for cap_inode_getsecurity(), because that module has no
secctx that ever needs releasing. It turns out that Smack is the
one that's doing things wrong by not allocating memory when instructed
to do so by the "alloc" parameter.

The fix is simple enough. Change the security_release_secctx() to
kfree() because it isn't a secctx being returned by
security_inode_getsecurity(). Change Smack to allocate the string when
told to do so.

Note: this also fixes memory leaks for LSMs which implement
inode_getsecurity but not release_secctx, such as capabilities.

Signed-off-by: Casey Schaufler <casey@...aufler-ca.com>
Reported-by: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
Signed-off-by: James Morris <james.l.morris@...cle.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/xattr.c                 |  2 +-
 security/smack/smack_lsm.c | 55 +++++++++++++++++++++-------------------------
 2 files changed, 26 insertions(+), 31 deletions(-)

--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -163,7 +163,7 @@ xattr_getsecurity(struct inode *inode, c
 	}
 	memcpy(value, buffer, len);
 out:
-	security_release_secctx(buffer, len);
+	kfree(buffer);
 out_noalloc:
 	return len;
 }
--- a/security/smack/smack_lsm.c
+++ b/security/smack/smack_lsm.c
@@ -1060,7 +1060,7 @@ static int smack_inode_removexattr(struc
  * @inode: the object
  * @name: attribute name
  * @buffer: where to put the result
- * @alloc: unused
+ * @alloc: duplicate memory
  *
  * Returns the size of the attribute or an error code
  */
@@ -1073,43 +1073,38 @@ static int smack_inode_getsecurity(const
 	struct super_block *sbp;
 	struct inode *ip = (struct inode *)inode;
 	char *isp;
-	int ilen;
-	int rc = 0;
 
-	if (strcmp(name, XATTR_SMACK_SUFFIX) == 0) {
+	if (strcmp(name, XATTR_SMACK_SUFFIX) == 0)
 		isp = smk_of_inode(inode);
-		ilen = strlen(isp);
-		*buffer = isp;
-		return ilen;
+	else {
+		/*
+		 * The rest of the Smack xattrs are only on sockets.
+		 */
+		sbp = ip->i_sb;
+		if (sbp->s_magic != SOCKFS_MAGIC)
+			return -EOPNOTSUPP;
+
+		sock = SOCKET_I(ip);
+		if (sock == NULL || sock->sk == NULL)
+			return -EOPNOTSUPP;
+
+		ssp = sock->sk->sk_security;
+
+		if (strcmp(name, XATTR_SMACK_IPIN) == 0)
+			isp = ssp->smk_in->smk_known;
+		else if (strcmp(name, XATTR_SMACK_IPOUT) == 0)
+			isp = ssp->smk_out->smk_known;
+		else
+			return -EOPNOTSUPP;
 	}
 
-	/*
-	 * The rest of the Smack xattrs are only on sockets.
-	 */
-	sbp = ip->i_sb;
-	if (sbp->s_magic != SOCKFS_MAGIC)
-		return -EOPNOTSUPP;
-
-	sock = SOCKET_I(ip);
-	if (sock == NULL || sock->sk == NULL)
-		return -EOPNOTSUPP;
-
-	ssp = sock->sk->sk_security;
-
-	if (strcmp(name, XATTR_SMACK_IPIN) == 0)
-		isp = ssp->smk_in->smk_known;
-	else if (strcmp(name, XATTR_SMACK_IPOUT) == 0)
-		isp = ssp->smk_out->smk_known;
-	else
-		return -EOPNOTSUPP;
-
-	ilen = strlen(isp);
-	if (rc == 0) {
-		*buffer = isp;
-		rc = ilen;
+	if (alloc) {
+		*buffer = kstrdup(isp, GFP_KERNEL);
+		if (*buffer == NULL)
+			return -ENOMEM;
 	}
 
-	return rc;
+	return strlen(isp);
 }