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Re: [libvirt] [PATCH 1/2] util: Don't fail virGetUserIDByName when user not found



On 12/05/12 13:03, Christophe Fergeau wrote:
virGetUserIDByName is documented as returning 1 if the username
cannot be found. getpwnam_r is documented as returning:
« 0 or ENOENT or ESRCH or EBADF or EPERM or ...  The given name
or uid was not found. »
  and that:
« The formulation given above under "RETURN VALUE" is from POSIX.1-2001.
It  does  not  call  "not  found"  an error, hence does not specify what
value errno might have in this situation.  But that makes it impossible to
recognize errors.  One might argue that according to POSIX errno should be
left unchanged if an entry is not found.  Experiments on various UNIX-like
systems shows that lots of different values occur in this situation: 0,
ENOENT, EBADF, ESRCH, EWOULDBLOCK, EPERM and probably others. »

virGetUserIDByName returns an error when the return value of getpwnam_r
is non-0. However on my RHEL system, getpwnam_r returns ENOENT when the
requested user cannot be found, which then causes virGetUserID not
to behave as documented (it returns an error instead of falling back
to parsing the passed-in value as an uid).

This commit makes virGetUserIDByName ignore the various values listed
in getpwnam_r manpage and return a 'user not found' result in such
cases.
---
  src/util/util.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/util/util.c b/src/util/util.c
index 2fd0f2c..df1af7e 100644
--- a/src/util/util.c
+++ b/src/util/util.c
@@ -2530,7 +2530,8 @@ virGetUserIDByName(const char *name, uid_t *uid)
          }
      }

-    if (rc != 0) {
+    if ((rc != 0) && (rc != ENOENT) && (rc != ESRCH)
+                  && (rc != EBADF) && (rc != EPERM)) {
          virReportSystemError(rc, _("Failed to get user record for name '%s'"),
                               name);
          goto cleanup;


Hm, this is the most elegant solution to the problem I came across. getpwent_r suggested by Osier isn't reentrant as one would think and other options would require too invasive changes into this code.

As we've already had such an error handling previously I'm in favor of taking this change.

ACK with formatting fixed as Osier suggested and this comment:
    /*
     * From the manpage (terrifying but true):
     *
     * ERRORS
     *  0 or ENOENT or ESRCH or EBADF or EPERM or ...
     *        The given name or uid was not found.
     */

placed before the call of the getpwnam_r function. (It was there before.)

Peter


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