Re: [syzbot] WARNING in mntput_no_expire (2)

Al Viro
2021-04-04T02:38:36Z

On Sun, Apr 04, 2021 at 02:34:08AM +0000, Al Viro wrote:

> I really wonder what mount is it happening to. BTW, how painful would
> it be to teach syzcaller to turn those cascades of
> NONFAILING(*(uint8_t*)0x20000080 = 0x12);
> NONFAILING(*(uint8_t*)0x20000081 = 0);
> NONFAILING(*(uint16_t*)0x20000082 = 0);
> NONFAILING(*(uint32_t*)0x20000084 = 0xffffff9c);
> NONFAILING(*(uint64_t*)0x20000088 = 0);
> NONFAILING(*(uint64_t*)0x20000090 = 0x20000180);
> NONFAILING(memcpy((void*)0x20000180, "./file0\000", 8));
> NONFAILING(*(uint32_t*)0x20000098 = 0);
> NONFAILING(*(uint32_t*)0x2000009c = 0x80);
> NONFAILING(*(uint64_t*)0x200000a0 = 0x23456);
> ....
> NONFAILING(syz_io_uring_submit(r[1], r[2], 0x20000080, 0));
> into something more readable? Bloody annoyance every time... Sure, I can
> manually translate it into
> struct io_uring_sqe *sqe = (void *)0x20000080;
> char *s = (void *)0x20000180;
> memset(sqe, '\0', sizeof(*sqe));
> sqe->opcode = 0x12; // IORING_OP_OPENAT?
> sqe->fd = -100; // AT_FDCWD?
> sqe->addr = s;
> strcpy(s, "./file0");
> sqe->open_flags = 0x80; // O_EXCL???
> sqe->user_data = 0x23456; // random tag?
> syz_io_uring_submit(r[1], r[2], (unsigned long)p, 0);
> but it's really annoying as hell, especially since syz_io_uring_submit()
> comes from syzcaller and the damn thing _knows_ that the third argument
> is sodding io_uring_sqe, and never passed to anything other than
> memcpy() in there, at that, so the exact address can't matter.

... especially since the native syzcaller reproducer clearly *does* have
that information. Simply putting that into comments side-by-side with
what gets put into C reproducer would be nice, especially if it goes with
field names...