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sunrpc: fix client side handling of tls alerts 

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: dea034b963 ("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>
This commit is contained in:
Olga Kornievskaia 2025-07-31 14:00:56 -04:00 committed by Trond Myklebust
parent 533210f239
commit cc5d59081f
1 changed files with 30 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

40
net/sunrpc/xprtsock.c
View File

@ -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