From 1f466e1f15cf1dac7c86798d694649fc42cd868a Mon Sep 17 00:00:00 2001 From: Christoph Hellwig Date: Mon, 11 May 2020 13:59:13 +0200 Subject: net: cleanly handle kernel vs user buffers for ->msg_control The msg_control field in struct msghdr can either contain a user pointer when used with the recvmsg system call, or a kernel pointer when used with sendmsg. To complicate things further kernel_recvmsg can stuff a kernel pointer in and then use set_fs to make the uaccess helpers accept it. Replace it with a union of a kernel pointer msg_control field, and a user pointer msg_control_user one, and allow kernel_recvmsg operate on a proper kernel pointer using a bitfield to override the normal choice of a user pointer for recvmsg. Signed-off-by: Christoph Hellwig Signed-off-by: David S. Miller --- net/core/scm.c | 49 ++++++++++++++++++++++++++++--------------------- 1 file changed, 28 insertions(+), 21 deletions(-) (limited to 'net/core/scm.c') diff --git a/net/core/scm.c b/net/core/scm.c index 168b006a52ff..a75cd637a71f 100644 --- a/net/core/scm.c +++ b/net/core/scm.c @@ -212,16 +212,12 @@ EXPORT_SYMBOL(__scm_send); int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data) { - struct cmsghdr __user *cm - = (__force struct cmsghdr __user *)msg->msg_control; - struct cmsghdr cmhdr; int cmlen = CMSG_LEN(len); - int err; - if (MSG_CMSG_COMPAT & msg->msg_flags) + if (msg->msg_flags & MSG_CMSG_COMPAT) return put_cmsg_compat(msg, level, type, len, data); - if (cm==NULL || msg->msg_controllen < sizeof(*cm)) { + if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) { msg->msg_flags |= MSG_CTRUNC; return 0; /* XXX: return error? check spec. */ } @@ -229,23 +225,30 @@ int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data) msg->msg_flags |= MSG_CTRUNC; cmlen = msg->msg_controllen; } - cmhdr.cmsg_level = level; - cmhdr.cmsg_type = type; - cmhdr.cmsg_len = cmlen; - - err = -EFAULT; - if (copy_to_user(cm, &cmhdr, sizeof cmhdr)) - goto out; - if (copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm))) - goto out; - cmlen = CMSG_SPACE(len); - if (msg->msg_controllen < cmlen) - cmlen = msg->msg_controllen; + + if (msg->msg_control_is_user) { + struct cmsghdr __user *cm = msg->msg_control_user; + struct cmsghdr cmhdr; + + cmhdr.cmsg_level = level; + cmhdr.cmsg_type = type; + cmhdr.cmsg_len = cmlen; + if (copy_to_user(cm, &cmhdr, sizeof cmhdr) || + copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm))) + return -EFAULT; + } else { + struct cmsghdr *cm = msg->msg_control; + + cm->cmsg_level = level; + cm->cmsg_type = type; + cm->cmsg_len = cmlen; + memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm)); + } + + cmlen = min(CMSG_SPACE(len), msg->msg_controllen); msg->msg_control += cmlen; msg->msg_controllen -= cmlen; - err = 0; -out: - return err; + return 0; } EXPORT_SYMBOL(put_cmsg); @@ -328,6 +331,10 @@ void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm) return; } + /* no use for FD passing from kernel space callers */ + if (WARN_ON_ONCE(!msg->msg_control_is_user)) + return; + for (i = 0; i < fdmax; i++) { err = __scm_install_fd(scm->fp->fp[i], cmsg_data + i, o_flags); if (err) -- cgit v1.2.3-59-g8ed1b