On Sun, Sep 13, 2020 at 11:26:39AM +0530, Anant Thazhemadam wrote:
> The crash report showed that there was a local variable;
>
> ----iovstack.i@__sys_sendmmsg created at:
> ___sys_sendmsg net/socket.c:2388 [inline]
> __sys_sendmmsg+0x6db/0xc90 net/socket.c:2480
>
> that was left uninitialized.
>
> The contents of iovstack are of interest, since the respective pointer
> is passed down as an argument to sendmsg_copy_msghdr as well.
> Initializing this contents of this stack prevents this bug from happening.
>
> Since the memory that was initialized is freed at the end of the function
> call, memory leaks are not likely to be an issue.
>
> syzbot seems to have triggered this error by passing an array of 0's as
> a parameter while making the initial system call.
>
> Reported-by: syzbot+09a5d591c1f98cf5e...@syzkaller.appspotmail.com
> Tested-by: syzbot+09a5d591c1f98cf5e...@syzkaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhema...@gmail.com>
> ---
> net/socket.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/socket.c b/net/socket.c
> index 0c0144604f81..d74443dfd73b 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2396,6 +2396,7 @@ static int ___sys_sendmsg(struct socket *sock, struct
> user_msghdr __user *msg,
> {
> struct sockaddr_storage address;
> struct iovec iovstack[UIO_FASTIOV], *iov = iovstack;
> + memset(iov, 0, UIO_FASTIOV);
> ssize_t err;
>
> msg_sys->msg_name = &address;
I don't think you built this code change, otherwise you would have seen
that it adds a build warning to the system, right?
:(
