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Commit 8beeb76a authored by Andy Lutomirski's avatar Andy Lutomirski Committed by Ben Hutchings
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net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg 

[ Upstream commits 1be374a0 and
  a7526eb5 ]

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: default avatarAndy Lutomirski <luto@amacapital.net>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarBen Hutchings <ben@decadent.org.uk>
parent 94e7239c
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Inline Side-by-side
Showing with 59 additions and 24 deletions
include/linux/socket.h
View file @ 8beeb76a
......@@ -336,6 +336,9 @@ extern int put_cmsg(struct msghdr*, int level, int type, int len, void *data);
struct timespec;
/* The __sys_...msg variants allow MSG_CMSG_COMPAT */
extern long __sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags);
extern long __sys_sendmsg(int fd, struct msghdr __user *msg, unsigned flags);
extern int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
unsigned int flags, struct timespec *timeout);
extern int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg,
......
net/compat.c
View file @ 8beeb76a
......@@ -733,19 +733,25 @@ static unsigned char nas[21] = {
asmlinkage long compat_sys_sendmsg(int fd, struct compat_msghdr __user *msg, unsigned flags)
{
return sys_sendmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_sendmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
}
asmlinkage long compat_sys_sendmmsg(int fd, struct compat_mmsghdr __user *mmsg,
unsigned vlen, unsigned int flags)
{
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_sendmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
flags | MSG_CMSG_COMPAT);
}
asmlinkage long compat_sys_recvmsg(int fd, struct compat_msghdr __user *msg, unsigned int flags)
{
return sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_recvmsg(fd, (struct msghdr __user *)msg, flags | MSG_CMSG_COMPAT);
}
asmlinkage long compat_sys_recv(int fd, void __user *buf, size_t len, unsigned flags)
......@@ -767,6 +773,9 @@ asmlinkage long compat_sys_recvmmsg(int fd, struct compat_mmsghdr __user *mmsg,
int datagrams;
struct timespec ktspec;
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
if (timeout == NULL)
return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
flags | MSG_CMSG_COMPAT, NULL);
......
net/socket.c
View file @ 8beeb76a
......@@ -1876,9 +1876,9 @@ struct used_address {
unsigned int name_len;
};
static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
struct msghdr *msg_sys, unsigned flags,
struct used_address *used_address)
static int ___sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
struct msghdr *msg_sys, unsigned flags,
struct used_address *used_address)
{
struct compat_msghdr __user *msg_compat =
(struct compat_msghdr __user *)msg;
......@@ -1998,22 +1998,30 @@ static int __sys_sendmsg(struct socket *sock, struct msghdr __user *msg,
* BSD sendmsg interface
*/
SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned, flags)
long __sys_sendmsg(int fd, struct msghdr __user *msg, unsigned flags)
{
int fput_needed, err;
struct msghdr msg_sys;
struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
struct socket *sock;
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (!sock)
goto out;
err = __sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
err = ___sys_sendmsg(sock, msg, &msg_sys, flags, NULL);
fput_light(sock->file, fput_needed);
out:
return err;
}
SYSCALL_DEFINE3(sendmsg, int, fd, struct msghdr __user *, msg, unsigned int, flags)
{
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_sendmsg(fd, msg, flags);
}
/*
* Linux sendmmsg interface
*/
......@@ -2044,15 +2052,16 @@ int __sys_sendmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
while (datagrams < vlen) {
if (MSG_CMSG_COMPAT & flags) {
err = __sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
&msg_sys, flags, &used_address);
err = ___sys_sendmsg(sock, (struct msghdr __user *)compat_entry,
&msg_sys, flags, &used_address);
if (err < 0)
break;
err = __put_user(err, &compat_entry->msg_len);
++compat_entry;
} else {
err = __sys_sendmsg(sock, (struct msghdr __user *)entry,
&msg_sys, flags, &used_address);
err = ___sys_sendmsg(sock,
(struct msghdr __user *)entry,
&msg_sys, flags, &used_address);
if (err < 0)
break;
err = put_user(err, &entry->msg_len);
......@@ -2076,11 +2085,13 @@ 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);
}
static int __sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
struct msghdr *msg_sys, unsigned flags, int nosec)
static int ___sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
struct msghdr *msg_sys, unsigned flags, int nosec)
{
struct compat_msghdr __user *msg_compat =
(struct compat_msghdr __user *)msg;
......@@ -2177,23 +2188,31 @@ static int __sys_recvmsg(struct socket *sock, struct msghdr __user *msg,
* BSD recvmsg interface
*/
SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
unsigned int, flags)
long __sys_recvmsg(int fd, struct msghdr __user *msg, unsigned flags)
{
int fput_needed, err;
struct msghdr msg_sys;
struct socket *sock = sockfd_lookup_light(fd, &err, &fput_needed);
struct socket *sock;
sock = sockfd_lookup_light(fd, &err, &fput_needed);
if (!sock)
goto out;
err = __sys_recvmsg(sock, msg, &msg_sys, flags, 0);
err = ___sys_recvmsg(sock, msg, &msg_sys, flags, 0);
fput_light(sock->file, fput_needed);
out:
return err;
}
SYSCALL_DEFINE3(recvmsg, int, fd, struct msghdr __user *, msg,
unsigned int, flags)
{
if (flags & MSG_CMSG_COMPAT)
return -EINVAL;
return __sys_recvmsg(fd, msg, flags);
}
/*
* Linux recvmmsg interface
*/
......@@ -2231,17 +2250,18 @@ int __sys_recvmmsg(int fd, struct mmsghdr __user *mmsg, unsigned int vlen,
* No need to ask LSM for more than the first datagram.
*/
if (MSG_CMSG_COMPAT & flags) {
err = __sys_recvmsg(sock, (struct msghdr __user *)compat_entry,
&msg_sys, flags & ~MSG_WAITFORONE,
datagrams);
err = ___sys_recvmsg(sock, (struct msghdr __user *)compat_entry,
&msg_sys, flags & ~MSG_WAITFORONE,
datagrams);
if (err < 0)
break;
err = __put_user(err, &compat_entry->msg_len);
++compat_entry;
} else {
err = __sys_recvmsg(sock, (struct msghdr __user *)entry,
&msg_sys, flags & ~MSG_WAITFORONE,
datagrams);
err = ___sys_recvmsg(sock,
(struct msghdr __user *)entry,
&msg_sys, flags & ~MSG_WAITFORONE,
datagrams);
if (err < 0)
break;
err = put_user(err, &entry->msg_len);
......@@ -2308,6 +2328,9 @@ 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);
......
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