Re: [PATCH v2] net: fix uninit value error in __sys_sendmmsg

Anant Thazhemadam
2020-09-14T08:16:55Z

On 13/09/20 4:33 pm, Anant Thazhemadam wrote:
> The crash report indicated 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.
>
> Initializing this stack to 0s prevents this bug from happening.
> Since the memory pointed to by *iov 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 system call.
>
> Reported-by: syzbot+09a5d591c1f98cf5efcb@syzkaller.appspotmail.com
> Tested-by: syzbot+09a5d591c1f98cf5efcb@syzkaller.appspotmail.com
> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
> ---
> Changes from v1:
> * Fixed the build warning that v1 had introduced
> net/socket.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/net/socket.c b/net/socket.c
> index 0c0144604f81..1e6f9b54982c 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2398,6 +2398,7 @@ static int ___sys_sendmsg(struct socket *sock, struct user_msghdr __user *msg,
> struct iovec iovstack[UIO_FASTIOV], *iov = iovstack;
> ssize_t err;
>
> + memset(iov, 0, UIO_FASTIOV);
> msg_sys->msg_name = &address;
>
> err = sendmsg_copy_msghdr(msg_sys, msg, flags, &iov);
It has since been determined that this patch is incorrect, and even if it were correct,
provides a huge performance overhead, that is not welcome. Kindly ignore this patch.
Sorry.

Thanks,
Anant