From c5794709bc9105935dbedef8b9cf9c06f2b559fa Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Tue, 17 Feb 2026 20:28:29 -0800 Subject: [PATCH 1/2] ksmbd: Compare MACs in constant time 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 Acked-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/Kconfig | 1 + fs/smb/server/auth.c | 4 +++- fs/smb/server/smb2pdu.c | 5 +++-- 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/fs/smb/server/Kconfig b/fs/smb/server/Kconfig index 2775162c535c..12594879cb64 100644 --- a/fs/smb/server/Kconfig +++ b/fs/smb/server/Kconfig @@ -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 diff --git a/fs/smb/server/auth.c b/fs/smb/server/auth.c index 580c4d303dc3..5fe8c667c6b1 100644 --- a/fs/smb/server/auth.c +++ b/fs/smb/server/auth.c @@ -15,6 +15,7 @@ #include #include #include +#include #include #include @@ -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; } diff --git a/fs/smb/server/smb2pdu.c b/fs/smb/server/smb2pdu.c index 95901a78951c..743c629fe7ec 100644 --- a/fs/smb/server/smb2pdu.c +++ b/fs/smb/server/smb2pdu.c @@ -4,6 +4,7 @@ * Copyright (C) 2018 Samsung Electronics Co., Ltd. */ +#include #include #include #include @@ -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; } From 6b4f875aac344cdd52a1f34cc70ed2f874a65757 Mon Sep 17 00:00:00 2001 From: Nicholas Carlini Date: Thu, 19 Feb 2026 20:58:57 +0900 Subject: [PATCH 2/2] ksmbd: fix signededness bug in smb_direct_prepare_negotiation() smb_direct_prepare_negotiation() casts an unsigned __u32 value from sp->max_recv_size and req->preferred_send_size to a signed int before computing min_t(int, ...). A maliciously provided preferred_send_size of 0x80000000 will return as smaller than max_recv_size, and then be used to set the maximum allowed alowed receive size for the next message. By sending a second message with a large value (>1420 bytes) the attacker can then achieve a heap buffer overflow. This fix replaces min_t(int, ...) with min_t(u32) Fixes: 0626e6641f6b ("cifsd: add server handler for central processing and tranport layers") Signed-off-by: Nicholas Carlini Reviewed-by: Stefan Metzmacher Acked-by: Stefan Metzmacher Acked-by: Namjae Jeon Signed-off-by: Steve French --- fs/smb/server/transport_rdma.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/smb/server/transport_rdma.c b/fs/smb/server/transport_rdma.c index 7c53b78b818e..188572491d53 100644 --- a/fs/smb/server/transport_rdma.c +++ b/fs/smb/server/transport_rdma.c @@ -2540,9 +2540,9 @@ static int smb_direct_prepare(struct ksmbd_transport *t) goto put; req = (struct smbdirect_negotiate_req *)recvmsg->packet; - sp->max_recv_size = min_t(int, sp->max_recv_size, + sp->max_recv_size = min_t(u32, sp->max_recv_size, le32_to_cpu(req->preferred_send_size)); - sp->max_send_size = min_t(int, sp->max_send_size, + sp->max_send_size = min_t(u32, sp->max_send_size, le32_to_cpu(req->max_receive_size)); sp->max_fragmented_send_size = le32_to_cpu(req->max_fragmented_size);