6.12-stable review patch. If anyone has any objections, please let me know.
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From: Olga Kornievskaia okorniev@redhat.com
[ Upstream commit cc5d59081fa26506d02de2127ab822f40d88bc5a ]
A security exploit was discovered in NFS over TLS in tls_alert_recv due to its assumption that there is valid data in the msghdr's iterator's kvec.
Instead, this patch proposes the rework how control messages are setup and used by sock_recvmsg().
If no control message structure is setup, kTLS layer will read and process TLS data record types. As soon as it encounters a TLS control message, it would return an error. At that point, NFS can setup a kvec backed control buffer and read in the control message such as a TLS alert. Scott found that a msg iterator can advance the kvec pointer as a part of the copy process thus we need to revert the iterator before calling into the tls_alert_recv.
Fixes: dea034b963c8 ("SUNRPC: Capture CMSG metadata on client-side receive") Suggested-by: Trond Myklebust trondmy@hammerspace.com Suggested-by: Scott Mayhew smayhew@redhat.com Signed-off-by: Olga Kornievskaia okorniev@redhat.com Link: https://lore.kernel.org/r/20250731180058.4669-3-okorniev@redhat.com Signed-off-by: Trond Myklebust trond.myklebust@hammerspace.com Signed-off-by: Sasha Levin sashal@kernel.org --- net/sunrpc/xprtsock.c | 40 ++++++++++++++++++++++++++++++---------- 1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c index 67d099c7c662..1397bb48cdde 100644 --- a/net/sunrpc/xprtsock.c +++ b/net/sunrpc/xprtsock.c @@ -358,7 +358,7 @@ xs_alloc_sparse_pages(struct xdr_buf *buf, size_t want, gfp_t gfp)
static int xs_sock_process_cmsg(struct socket *sock, struct msghdr *msg, - struct cmsghdr *cmsg, int ret) + unsigned int *msg_flags, struct cmsghdr *cmsg, int ret) { u8 content_type = tls_get_record_type(sock->sk, cmsg); u8 level, description; @@ -371,7 +371,7 @@ xs_sock_process_cmsg(struct socket *sock, struct msghdr *msg, * record, even though there might be more frames * waiting to be decrypted. */ - msg->msg_flags &= ~MSG_EOR; + *msg_flags &= ~MSG_EOR; break; case TLS_RECORD_TYPE_ALERT: tls_alert_recv(sock->sk, msg, &level, &description); @@ -386,19 +386,33 @@ xs_sock_process_cmsg(struct socket *sock, struct msghdr *msg, }
static int -xs_sock_recv_cmsg(struct socket *sock, struct msghdr *msg, int flags) +xs_sock_recv_cmsg(struct socket *sock, unsigned int *msg_flags, int flags) { union { struct cmsghdr cmsg; u8 buf[CMSG_SPACE(sizeof(u8))]; } u; + u8 alert[2]; + struct kvec alert_kvec = { + .iov_base = alert, + .iov_len = sizeof(alert), + }; + struct msghdr msg = { + .msg_flags = *msg_flags, + .msg_control = &u, + .msg_controllen = sizeof(u), + }; int ret;
- msg->msg_control = &u; - msg->msg_controllen = sizeof(u); - ret = sock_recvmsg(sock, msg, flags); - if (msg->msg_controllen != sizeof(u)) - ret = xs_sock_process_cmsg(sock, msg, &u.cmsg, ret); + iov_iter_kvec(&msg.msg_iter, ITER_DEST, &alert_kvec, 1, + alert_kvec.iov_len); + ret = sock_recvmsg(sock, &msg, flags); + if (ret > 0 && + tls_get_record_type(sock->sk, &u.cmsg) == TLS_RECORD_TYPE_ALERT) { + iov_iter_revert(&msg.msg_iter, ret); + ret = xs_sock_process_cmsg(sock, &msg, msg_flags, &u.cmsg, + -EAGAIN); + } return ret; }
@@ -408,7 +422,13 @@ xs_sock_recvmsg(struct socket *sock, struct msghdr *msg, int flags, size_t seek) ssize_t ret; if (seek != 0) iov_iter_advance(&msg->msg_iter, seek); - ret = xs_sock_recv_cmsg(sock, msg, flags); + ret = sock_recvmsg(sock, msg, flags); + /* Handle TLS inband control message lazily */ + if (msg->msg_flags & MSG_CTRUNC) { + msg->msg_flags &= ~(MSG_CTRUNC | MSG_EOR); + if (ret == 0 || ret == -EIO) + ret = xs_sock_recv_cmsg(sock, &msg->msg_flags, flags); + } return ret > 0 ? ret + seek : ret; }
@@ -434,7 +454,7 @@ xs_read_discard(struct socket *sock, struct msghdr *msg, int flags, size_t count) { iov_iter_discard(&msg->msg_iter, ITER_DEST, count); - return xs_sock_recv_cmsg(sock, msg, flags); + return xs_sock_recvmsg(sock, msg, flags, 0); }
#if ARCH_IMPLEMENTS_FLUSH_DCACHE_PAGE