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 <hch@lst.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/scm.c b/net/core/scm.c
index 168b006..a75cd63 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)
