From 8beeb76aa534e9312fdae1c91ab3a2effc847ee5 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; } Cc: David S. Miller Signed-off-by: Andy Lutomirski Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings --- net/compat.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-) (limited to 'net/compat.c') diff --git a/net/compat.c b/net/compat.c index 6def90e0a112..8c979cccdbd9 100644 --- a/net/compat.c +++ b/net/compat.c @@ -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); -- cgit v1.2.3