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



On Thu, Dec 06, 2012 at 03:07:32PM +0100, Peter Krempa wrote:
> 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.

Another option could be to list the errno values for which we return
an error rather than listing the errno values for which we don't want to
return an error:


 if (rc != 0) {
    if ((rc == EINTR) || (rc == EIO) || (rc == EMFILE)
        || (rc == ENFILE) || (rc == ENOMEM)) {
        virReportSystemError(rc, _("Failed to get group record for name %s'"),
                             name);
        goto cleanup;
    }
 }


> 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.)

I'll also add an errno = 0; before the call as mentioned by Osier. I'll
send a v2 with these changes once you tell me if you prefer the old
filtering or the one suggested in this email. Thanks,

Christophe

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