[PATCH 5.15] ksmbd: Compare MACs in constant time

[Eric Biggers <ebiggers@kernel.org>]

commit c5794709bc9105935dbedef8b9cf9c06f2b559fa upstream.

To prevent timing attacks, MAC comparisons need to be constant-time.
Replace the memcmp() with the correct function, crypto_memneq().

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
---
 fs/ksmbd/auth.c    | 4 +++-
 fs/ksmbd/smb2pdu.c | 5 +++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/ksmbd/auth.c b/fs/ksmbd/auth.c
index 647692ca78a28..7a06139274172 100644
--- a/fs/ksmbd/auth.c
+++ b/fs/ksmbd/auth.c
@@ -11,10 +11,11 @@
 #include <linux/writeback.h>
 #include <linux/uio.h>
 #include <linux/xattr.h>
 #include <crypto/hash.h>
 #include <crypto/aead.h>
+#include <crypto/algapi.h>
 #include <linux/random.h>
 #include <linux/scatterlist.h>
 
 #include "auth.h"
 #include "glob.h"
@@ -279,11 +280,12 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
 	if (rc) {
 		ksmbd_debug(AUTH, "Could not generate sess key\n");
 		goto out;
 	}
 
-	if (memcmp(ntlmv2->ntlmv2_hash, ntlmv2_rsp, CIFS_HMAC_MD5_HASH_SIZE) != 0)
+	if (crypto_memneq(ntlmv2->ntlmv2_hash, ntlmv2_rsp,
+			  CIFS_HMAC_MD5_HASH_SIZE))
 		rc = -EINVAL;
 out:
 	if (ctx)
 		ksmbd_release_crypto_ctx(ctx);
 	kfree(construct);
diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
index b5ff4c855f9cb..829329abca664 100644
--- a/fs/ksmbd/smb2pdu.c
+++ b/fs/ksmbd/smb2pdu.c
@@ -2,10 +2,11 @@
 /*
  *   Copyright (C) 2016 Namjae Jeon <linkinjeon@kernel.org>
  *   Copyright (C) 2018 Samsung Electronics Co., Ltd.
  */
 
+#include <crypto/algapi.h>
 #include <linux/inetdevice.h>
 #include <net/addrconf.h>
 #include <linux/syscalls.h>
 #include <linux/namei.h>
 #include <linux/statfs.h>
@@ -8396,11 +8397,11 @@ int smb2_check_sign_req(struct ksmbd_work *work)
 
 	if (ksmbd_sign_smb2_pdu(work->conn, work->sess->sess_key, iov, 1,
 				signature))
 		return 0;
 
-	if (memcmp(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
 		pr_err("bad smb2 signature\n");
 		return 0;
 	}
 
 	return 1;
@@ -8484,11 +8485,11 @@ int smb3_check_sign_req(struct ksmbd_work *work)
 	iov[0].iov_len = len;
 
 	if (ksmbd_sign_smb3_pdu(conn, signing_key, iov, 1, signature))
 		return 0;
 
-	if (memcmp(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
+	if (crypto_memneq(signature, signature_req, SMB2_SIGNATURE_SIZE)) {
 		pr_err("bad smb2 signature\n");
 		return 0;
 	}
 
 	return 1;

base-commit: 91d48252ad4b17577cf8cc8d3e1353402e4da8f1
-- 
2.53.0