linux-kernel - Re: [patch 7/8] fdmap v2

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Message-Id: <20070607123937.db4a9f30.dada1@cosmosbay.com>
Date:	Thu, 7 Jun 2007 12:39:37 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	Ingo Molnar <mingo@...e.hu>
Subject: Re: [patch 7/8] fdmap v2 - implement sys_socket2

Davide Libenzi <davidel@...ilserver.org> wrote:

> The sys_accept() system call has been modified to return a file
> descriptor inside the non-sequential area, if the listening fd is.

> -   newfd = sock_alloc_fd(&newfile);
> +   newfd = sock_alloc_fd(&newfile,
> +         fd > current->signal->rlim[RLIMIT_NOFILE].rlim_cur ? O_NONSEQFD: 0);

This will break apps that change/downgrade their rlimit (after getting a high fd listen socket)
Yes probably insane, but who knows...

sock = socket(...);
bind(...);
listen(sock, backlog); ...
fd = dup2(sock, 1023);
close(sock);

setrlimit( RLIMIT_NOFILE, rlim.rlim_cur = 256);
...
while ((newsock = accept(fd, ...)) != -1) {
     fork();...
     Plain legacy code, expecting newsock being *small*
     FD_SET(newsock , &rd_set);
     ...oops... fd is too large to fit in fd_set
     select(newsock + 1, &rd_set, ...);
     }


So you might change logic to straight :

newfd = sock_alloc_fd(&newfile, (fd >= FDMAP_NONSEQ_BASE) ? O_NONSEQFD: 0);

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