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Message-ID: <261b4d35-9075-8b1f-ccb3-fd5654200ae4@gmail.com>
Date: Wed, 5 Oct 2016 17:56:40 -0400
From: Assaf Gordon <assafgordon@...il.com>
To: musl@...ts.openwall.com
Subject: possible bug in getdtablesize() ?
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.
regards,
- assaf
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