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Date: Wed, 5 Oct 2016 19:00:50 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com
Subject: Re: possible bug in getdtablesize() ?
On Wed, Oct 05, 2016 at 05:56:40PM -0400, Assaf Gordon wrote:
> Hello,
>
> It seems that musl's getdtablesize() returns incorrect value,
> possibly using the "rlim_max" instead of "rlim_cur" value (just a guess, not sure about the actual reason).
>
> The following code demonstrates: trying to use dup2(2) on a file-descriptor value that "should work".
>
> #include <unistd.h>
> #include <stdio.h>
> #include <err.h>
>
> int main(void)
> {
> int fd = STDIN_FILENO;
> int maxfd = getdtablesize();
> printf("maxfd = %d\n", maxfd);
>
> int newfd = maxfd-1;
>
> int i = dup2(fd,newfd);
> if (i == -1)
> err(1,"dup2(%d, %d) failed", fd, newfd);
>
> if (i != newfd)
> errx(1,"dup2(%d, %d) returned %d", fd, newfd, i);
>
> return 0;
> }
>
>
> With glibc, it works:
>
> $ gcc -o dup2-glibc dup2-test.c
> $ strace -e prlimit64,getrlimit,dup2 ./dup2-glibc
> getrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=4*1024}) = 0
> maxfd = 1024
> dup2(0, 1023) = 1023
> +++ exited with 0 +++
>
> With musl-1.1.15, it failsdue to wrong 'max-fd' value:
>
> $ musl-gcc -o dup2-musl dup2-test.c
> $ strace -e prlimit64,getrlimit,dup2 ./dup2-musl
> prlimit64(0, RLIMIT_NOFILE, NULL, {rlim_cur=1024, rlim_max=4*1024}) = 0
> maxfd = 4096
> dup2(0, 4095) = -1 EBADF (Bad file descriptor)
> dup2-musl: dup2(0, 4095) failed: Bad file descriptor
> +++ exited with 1 +++
>
> Using:
>
> $ uname -svr
> Linux 3.13.0-88-generic #135-Ubuntu SMP Wed Jun 8 21:10:42 UTC 2016
>
> $ gcc --version
> gcc (GCC) 5.2.0
>
> $ ulimit -a
> [...]
> open files (-n) 1024
>
> and glibc-2.19.
This is already fixed in git master, as of:
https://git.musl-libc.org/cgit/musl/commit/?id=397586625e71d166f493f16bfe04f3005ae464c3
I'll try to roll a new release soon with this and other fixes.
Rich
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