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ksmbd: Compare MACs in constant time

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

Fixes: e2f34481b2 ("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>
This commit is contained in:
Eric Biggers 2026-02-17 20:28:29 -08:00 • committed by Steve French
parent 6de23f81a5
commit c5794709bc
3 changed files with 7 additions and 3 deletions
Download patch file Download diff file Expand all files Collapse all files

1
fs/smb/server/Kconfig
View file

@ -13,6 +13,7 @@ config SMB_SERVER
select CRYPTO_LIB_MD5
select CRYPTO_LIB_SHA256
select CRYPTO_LIB_SHA512
select CRYPTO_LIB_UTILS
select CRYPTO_CMAC
select CRYPTO_AEAD2
select CRYPTO_CCM

4
fs/smb/server/auth.c
View file

@ -15,6 +15,7 @@
#include <crypto/aead.h>
#include <crypto/md5.h>
#include <crypto/sha2.h>
#include <crypto/utils.h>
#include <linux/random.h>
#include <linux/scatterlist.h>
@ -165,7 +166,8 @@ int ksmbd_auth_ntlmv2(struct ksmbd_conn *conn, struct ksmbd_session *sess,
ntlmv2_rsp, CIFS_HMAC_MD5_HASH_SIZE,
sess->sess_key);
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))
return -EINVAL;
return 0;
}

5
fs/smb/server/smb2pdu.c
View file

@ -4,6 +4,7 @@
* Copyright (C) 2018 Samsung Electronics Co., Ltd.
*/
#include <crypto/utils.h>
#include <linux/inetdevice.h>
#include <net/addrconf.h>
#include <linux/syscalls.h>
@ -8880,7 +8881,7 @@ int smb2_check_sign_req(struct ksmbd_work *work)
ksmbd_sign_smb2_pdu(work->conn, work->sess->sess_key, iov, 1,
signature);
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;
}
@ -8968,7 +8969,7 @@ int smb3_check_sign_req(struct ksmbd_work *work)
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;
}