ssh_poll_ctx_dopoll: Sometimes returns 1 instead of SSH_{OK,ERROR,AGAIN}

[poptsov.artyom@xxxxxxxxx (Artyom V. Poptsov)]

Hello,

I found that in some cases 'ssh_poll_ctx_dopoll' procedure from 'poll.c'
(libssh 0.9.0) returns 1 instead of a valid SSH_{OK,ERROR,AGAIN} code.
This seems to be wrong according to the commentary written above the
procedure.

My application (Guile-SSH) fails approximately 4 out of 5 times due to
this libssh behavior as I do 'assert (0)' on the cases when
'ssh_channel_open_forward' returns unknown value (1, in my case.)

I'm investigating the problem and it seems that there are situations
when 'ssh_poll' returns 1 as the result, and 'used = ctx->polls_used'
yields to zero, so this loop[1] never executes and thus 'rc' value never
decreases to zero:

--8<---------------cut here---------------start------------->8---
    for (i = 0; i < used && rc > 0; ) {
        if (!ctx->pollfds[i].revents || ctx->pollptrs[i]->lock) {
            i++;
        } else {
            // ... skipped ...
            rc--;
        }
    }
--8<---------------cut here---------------end--------------->8---

In such case, the procedure returns 1.

I observe the same problem on the 'master' branch (c6460cc9).

I can prepare a patch when I figure out what is the right solution for
this.  Any help with that would be appreciated.

Thanks!

- Artyom

[1] https://git.libssh.org/projects/libssh.git/tree/src/poll.c?h=libssh-0.9.0#n690

-- 
Artyom V. Poptsov <poptsov.artyom@xxxxxxxxx>
Home page: http://poptsov-artyom.narod.ru/
CADR Hackerspace co-founder: https://cadrspace.ru/
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