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SubjectRe: 2.4.0-ac3 write() to tcp socket returning errno of -3 (ESRCH: "No such process")
On Sun, 7 Jan 2001, David S. Miller wrote:

> Date: Sun, 7 Jan 2001 23:55:28 -0600 (CST)
> From: Paul Cassella <pwc@speakeasy.net>
>
> [1.] One line summary of the problem:
>
> write() returns -1 and sets errno non-sensically. 2.4.0{,-ac[23]}
>
> What you describe I can only say is "impossible".

Right. That's why the code g_error()'s there. :)

> None of them can occur via TCP socket writes (only netlink socket
> operations or socket control calls).

I didn't imagine that a TCP write could return any of these errors, which
is why I guessed that something's returning a value it thinks is positive,
but turns out to be negative in this case, for example, "return a - b;"
where due to, maybe, (but I guess not,) the peer shrunk window thing, a < b.

> Therefore I suspect you are perhaps getting rather some form of memory
> corruption or similar, really, please search the networking code for
> ESRCH value usage, you will see.

I believe that the tcp_sendmsg() path never tries to return -ESRCH, but I
don't see how userland memory corruption could cause the app to (1) open
such a socket instead of a TCP socket, and (2) get ESRCH or ENOEXEC
instead of EPERM or whatever a non-root process would get when it tried
such a thing.

I have seen no signs of bad memory on this machine, and of a fairly small
sample set, one (I was wrong when I said several) person is seeing the
same thing, with 2.4.0-test13-pre4, and I didn't see it with
2.4.0-test11-pre2.

The change I made to linux/fs/read_write.c:sys_write() checks

file->f_op == &socket_file_ops

and then finds ret == -3; presumably this is the same 3 that my app gets.


Would it be more helpful if I were to check something like

socki_lookup(file->f_dentry->f_inode)->ops == tcp_prot

instead? Or do the check in tcp_sendmsg()?

--
Paul Cassella

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