From 1d3d1b23e1c8f52ec431ddaa8deea1322bc25cbf Mon Sep 17 00:00:00 2001 From: Jonas Schievink Date: Thu, 12 Jul 2018 00:12:44 +0200 Subject: [PATCH] Zero out the host's `msg_control` buffer If this is not done, qemu would drop any control message after the first one. This is because glibc's `CMSG_NXTHDR` macro accesses the uninitialized cmsghdr's length field in order to find out if the message fits into the `msg_control` buffer, wrongly assuming that it doesn't because the length field contains garbage. Accessing the length field is fine for completed messages we receive from the kernel, but is - as far as I know - not needed since the kernel won't return such an invalid cmsghdr in the first place. This is tracked as this glibc bug: https://sourceware.org/bugzilla/show_bug.cgi?id=13500 It's probably also a good idea to bail with an error if `CMSG_NXTHDR` returns NULL but `TARGET_CMSG_NXTHDR` doesn't (ie. we still expect cmsgs). Signed-off-by: Jonas Schievink Reviewed-by: Laurent Vivier Message-Id: <20180711221244.31869-1-jonasschievink@gmail.com> Signed-off-by: Laurent Vivier --- linux-user/syscall.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/linux-user/syscall.c b/linux-user/syscall.c index aa4f3eb1c8..3df3bdffb2 100644 --- a/linux-user/syscall.c +++ b/linux-user/syscall.c @@ -3843,6 +3843,8 @@ static abi_long do_sendrecvmsg_locked(int fd, struct target_msghdr *msgp, } msg.msg_controllen = 2 * tswapal(msgp->msg_controllen); msg.msg_control = alloca(msg.msg_controllen); + memset(msg.msg_control, 0, msg.msg_controllen); + msg.msg_flags = tswap32(msgp->msg_flags); count = tswapal(msgp->msg_iovlen);