[Bug libc/30737] New: fdopendir() is not robust - returns bogus DIR* instead of flagging an error

["markgaleck at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30737

            Bug ID: 30737
           Summary: fdopendir() is not robust - returns bogus DIR* instead
                    of flagging an error
           Product: glibc
           Version: 2.35
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: markgaleck at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

First, dislclaimer: I checked this issue is present on the latest Ubuntu
distribution, which has glibc version 2.35, not the latest stable 2.38.  I was
able to build 2.38 locally, but I am not able to force Ubuntu to accept it for
linking to the sample program, or to upgrade the installed glibc 2.35 to 2.38. 

If you know how to test the sample program with 2.38, please let me know, and I
will do so and I will remove this report if it does not reproduce with glibc
2.38.
---------------------------

Here is the SSCCE 
'foobar.c'

(which I obtained by necessary modifications to the sample code in man7 entry
for fdopendir() ) :


#define _GNU_SOURCE

#include <stdio.h>
#include <dirent.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>

int
main(int argc, char* argv[])
{
    DIR* d;
    struct dirent* dp;
    int dfd;

    if ((d = fdopendir(open("./dir", O_RDONLY | O_PATH | O_DIRECTORY))) ==
NULL) {
        fprintf(stderr, "Cannot open directory\n");
        exit(1);
    }

    while ((dp = readdir(d)) != NULL) {
        if (!strcmp(dp->d_name, "."))
            continue;
        if (!strcmp(dp->d_name, ".."))
            continue;
        printf("d_name %s\n", dp->d_name);
    }
    return 0;
}

-------------------------
Here is a script to show the problem:

$ mkdir dir
$ touch dir/file
$ gcc -lc foobar.c
$ ./a.out
$

When called on a descriptor opened with O_PATH , fdopendir() succeeds happily,
but then, readdir() reports nothing!

So the DIR* returned from fdopendir() is useless, but fdopendir() returns it,
instead of NULL and setting errno to EBADF , as it should INHO


If I remove | O_PATH from the above sample code, I get the expected result:

$gcc -lc foobar.c
$ ./a.out
d_name file

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