[Bug nscd/15139] getpwuid_r does not return ERANGE consistently

["carlos at redhat dot com" <sourceware-bugzilla@sourceware.org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=15139

Carlos O'Donell <carlos at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |WAITING
                 CC|                            |carlos at redhat dot com

--- Comment #1 from Carlos O'Donell <carlos at redhat dot com> 2013-02-13 16:26:58 UTC ---
Thomas,

The function is allowed to return ERANGE at *any* time and the user application
must grow the buffer. The fault is with Sigar here.

However, there is an orthogonal issue in that sysconf (_SC_GETPW_R_SIZE_MAX)
returns a static 1024 on Linux and that is technically too small for some
results. It is my opinion that it should return -1, indicating that there is no
limit and that it is up to the user to choose a reasonably large value and to
watch out for ERANGE.

If anything the bug is that sysconf (_SC_GETPW_R_SIZE_MAX) returns a limit,
that when used, is actually too small.

The correct solution on the glibc side is likely going to be to return -1 for
sysconf (_SC_GETPW_R_SIZE_MAX), and the fix on the Sigar side is going to be to
be to do something like this (completely off the top of my head with no
testing):

/* sysconf(_SC_GET{PW,GR}_R_SIZE_MAX) == -1, choose a reasonable buffer size. 
*/
#define R_SIZE_MAX 8192   /* Multiple of 2*R_SIZE_INIT */
#define R_SIZE_INIT 1024

...
# ifdef HAVE_GETPWUID_R
    struct passwd pwbuf;
    int saved_errno;
    char *buffer;
    /* Allocate an initial buffer.  */
    size_t buflen = R_SIZE_INIT;
    buffer = (char *) malloc (buflen);
    if (buffer == NULL)
      return errno;
    do {
      if (getpwuid_r(uid, &pwbuf, buffer, sizeof(buffer), &pw) != 0) {
        saved_errno = errno;
        /* We handle ERANGE, but anything else return as an error.  */
        if (errno != ERANGE)
          return errno;
        /* Double the buffer size and try again.  */
        buflen = buflen * 2;
        if (buflen > R_SIZE_MAX)
          /* We hit our own internal limit. Return artificial ENOMEM.  */
          return ENOMEM; 
        buffer = (char *) realloc (buffer, buflen);
        if (buffer == NULL)
          return errno;
      }
      if (!pw) {
          return ENOENT;
      }
    } while (saved_errno == ERANGE)
# else
...

Does that make sense?

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