On 13/09/20 11:43 am, Greg KH wrote:
> 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?
>
> :(
My apologies. I think I ended up overlooking the build warning. Thank you for
pointing that out.
If everything else looks good, I'd be happy to send in a v2 that fixes this
build warning.
Thanks,
Anant
