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net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg

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To: linux-kernel@vger.kernel.org
Cc: x86@kernel.org, trinity@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>, netdev@vger.kernel.org, "David S.
	Miller" <davem@davemloft.net>
Subject: [PATCH 5/5] net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg

MSG_CMSG_COMPAT is (AFAIK) not intended to be part of the API --
it's a hack that steals a bit to indicate to other networking code
that a compat entry was used.  So don't allow it from a non-compat
syscall.

This prevents an oops when running this code:

int main()
{
	int s;
	struct sockaddr_in addr;
	struct msghdr *hdr;

	char *highpage = mmap((void*)(TASK_SIZE_MAX - 4096), 4096,
	                      PROT_READ | PROT_WRITE,
	                      MAP_PRIVATE | MAP_ANONYMOUS | MAP_FIXED, -1, 0);
	if (highpage == MAP_FAILED)
		err(1, "mmap");

	s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
	if (s == -1)
		err(1, "socket");

        addr.sin_family = AF_INET;
        addr.sin_port = htons(1);
        addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
	if (connect(s, (struct sockaddr*)&addr, sizeof(addr)) != 0)
		err(1, "connect");

	void *evil = highpage + 4096 - COMPAT_MSGHDR_SIZE;
	printf("Evil address is %p\n", evil);

	if (syscall(__NR_sendmmsg, s, evil, 1, MSG_CMSG_COMPAT) < 0)
		err(1, "sendmmsg");

	return 0;
}

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Andy Lutomirski 2013-05-22 14:07:44 -07:00 committed by David S. Miller
parent f96ef988cc
commit 1be374a051
1 changed files with 31 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

33
net/socket.c
View file

@ -2075,8 +2075,12 @@ SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned int, fla
{
int fput_needed, err;
struct msghdr msg_sys;
struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
struct socket *sock;
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (!sock)
goto out;
@ -2149,6 +2153,8 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
SYSCALL_DEFINE4(sendmmsg, int, fd, struct mmsghdr __user *, mmsg,
unsigned int, vlen, unsigned int, flags)
{
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_sendmmsg(fd, mmsg, vlen, flags);
}
@ -2249,8 +2255,12 @@ SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
{
int fput_needed, err;
struct msghdr msg_sys;
struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
struct socket *sock;
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (!sock)
goto out;
@ -2375,6 +2385,9 @@ SYSCALL_DEFINE5(recvmmsg, int, fd, struct mmsghdr __user *, mmsg,
int datagrams;
struct timespec timeout_sys;
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
if (!timeout)
return __sys_recvmmsg(fd, mmsg, vlen, flags, NULL);
@ -2492,15 +2505,31 @@ SYSCALL_DEFINE2(socketcall, int, call, unsigned long __user *, args)
(int __user *)a[4]);
break;
case SYS_SENDMSG:
if (a[2] & MSG_CMSG_COMPAT) {
err = -EINVAL;
break;
}
err = sys_sendmsg(a0, (struct msghdr __user *)a1, a[2]);
break;
case SYS_SENDMMSG:
if (a[3] & MSG_CMSG_COMPAT) {
err = -EINVAL;
break;
}
err = sys_sendmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3]);
break;
case SYS_RECVMSG:
if (a[2] & MSG_CMSG_COMPAT) {
err = -EINVAL;
break;
}
err = sys_recvmsg(a0, (struct msghdr __user *)a1, a[2]);
break;
case SYS_RECVMMSG:
if (a[3] & MSG_CMSG_COMPAT) {
err = -EINVAL;
break;
}
err = sys_recvmmsg(a0, (struct mmsghdr __user *)a1, a[2], a[3],
(struct timespec __user *)a[4]);
break;