On 13/09/20 11:43 am, Greg KH wrote:

On Sun, Sep 13, 2020 at 11:26:39AM +0530, Anant Thazhemadam wrote:

quoted

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+09a5d591c1f98cf5efcb@syzkaller.appspotmail.com
Tested-by: syzbot+09a5d591c1f98cf5efcb@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <redacted>
---
 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
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