Re: WARNING in add_uevent_var

[Tetsuo Handa]

On 2018/04/03 21:34, Johannes Berg wrote:
> On Sun, 2018-04-01 at 23:01 -0700, syzbot wrote:
> 
>> So far this crash happened 5 times on net-next, upstream.
>> C reproducer: https://syzkaller.appspot.com/x/repro.c?id=6614377067184128
>>
> 
> Huh, fun. Looks like you're basically creating a new HWSIM radio with an
> insanely long name (4k!) and nothing stops you, until we try to generate
> an rfkill instance which sends a uevent and only has a 2k buffer for the
> environment variables, where we put the name ...
> 
> But yeah, we should probably limit the phy name to something sane, I'll
> pick 128 and send a patch.
> 

I think it should be NAME_MAX.

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#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <linux/netlink.h>

int main(int argc, char *argv[])
{
	const int fd = socket(PF_NETLINK, SOCK_RAW, NETLINK_GENERIC);
	static struct {
		struct nlmsghdr hdr;
		char data[4120 - sizeof(struct nlmsghdr)];
	} buf = { };
	struct sockaddr_nl addr = { .nl_family = AF_NETLINK };
	struct iovec iov = { &buf, sizeof(buf) };
	struct msghdr msg = {
		.msg_name = &addr,
		.msg_namelen = sizeof(addr),
		.msg_iov = &iov,
		.msg_iovlen = 1,
	};
	buf.hdr.nlmsg_len = 0x1018;
	buf.hdr.nlmsg_type = 0x22;
	buf.hdr.nlmsg_flags = 0x109;
	*(uint8_t*) buf.data = 4;
	*(uint8_t*) (buf.data + 1) = 0;
	*(uint16_t*) (buf.data + 2) = 0;
	*(uint16_t*) (buf.data + 4) = 0x1004;
	*(uint16_t*) (buf.data + 6) = 0x11;
	memset(buf.data + 8, 'A', 4096); /* strlen() > NAME_MAX */
	sendmsg(fd, &msg, 0);
	return 0;
}
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