net: Block MSG_CMSG_COMPAT in send(m)msg and recv(m)msg
[ Upstream commits 1be374a0518a288147c6a7398792583200a67261 and
a7526eb5d06b0084ef12d7b168d008fcf516caab ]
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;
}
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/net/compat.c b/net/compat.c
index ae6d67a..014e1c7 100644
--- a/net/compat.c
+++ b/net/compat.c
@@ -743,19 +743,25 @@
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)
@@ -777,6 +783,9 @@
int datagrams;
struct timespec ktspec;
+ if (flags & MSG_CMSG_COMPAT)
+ return -EINVAL;
+
if (COMPAT_USE_64BIT_TIME)
return __sys_recvmmsg(fd, (struct mmsghdr __user *)mmsg, vlen,
flags | MSG_CMSG_COMPAT,