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

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Date:	Thu, 7 Jun 2007 08:42:29 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Eric Dumazet <dada1@...mosbay.com>
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

On Thu, 7 Jun 2007, Eric Dumazet wrote:

> 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);

Yes, that makes perfectly sense to me.


- Davide


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