From c0cc94f2f65a682827cca2a79a4d045a20f8897f Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Wed, 22 May 2013 14:07:44 -0700 Subject: 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 Cc: David S. Miller Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- include/linux/socket.h | 3 +++ 1 file changed, 3 insertions(+) (limited to 'include') diff --git a/include/linux/socket.h b/include/linux/socket.h index 8f15b1d0031..9b54ebef173 100644 --- a/include/linux/socket.h +++ b/include/linux/socket.h @@ -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, -- cgit v1.2.3-18-g5258