Two problems getting user and group info from /etc/{passwd,group}

Two problems getting user and group info from /etc/{passwd,group}

[q q]

Dear Cygwin developers,

Can you please take a look? - We came across a couple problems (times two, because they're identical for /etc/group as well):

1.  When '/etc/passwd' gets reloaded, it can't add the last (default) line for uid=-1 because pretty_ls[] has already been parsed (':'s replaced with '\0'), and can't be parsed again.

2.  When there's fork(), a fresh copy of the pretty_ls seems to be loaded, which does not have '\0's in place of ':'s, while the parsed addressed are kept on heap and are still valid.

NOTE.  The default entry (uid=-1) is needed in case when code runs from a service account(NT SERVICE\...), which can't map to any POSIX UID/GID, so they fail back to -1.

The exposition is below, for each bug (WARNING: BUG1 will cause /etc/passwd to be "touch"ed):

$ gcc -DBUG1 pwd.c

$ ./a.exe
pw_name   = (0x6118ad2c)????????
pw_passwd = (0x6118ad35)*
pw_uid    = 4294967295
pw_gid    = 4294967295
pw_gecos  = (0x6118ad3d)
pw_dir    = (0x6118ad3e)
pw_shell  = (0x6118ad3f)

pwd = NULL


$ gcc -DBUG2 pwd.c

$ ./a.exe
pw_name   = (0x6118ad2c)????????
pw_passwd = (0x6118ad35)*
pw_uid    = 4294967295
pw_gid    = 4294967295
pw_gecos  = (0x6118ad3d)
pw_dir    = (0x6118ad3e)
pw_shell  = (0x6118ad3f)

pw_name   = (0x6118ad2c)????????:*:-1:-1:::
pw_passwd = (0x6118ad35)*:-1:-1:::
pw_uid    = 4294967295
pw_gid    = 4294967295
pw_gecos  = (0x6118ad3d)::
pw_dir    = (0x6118ad3e):
pw_shell  = (0x6118ad3f)


Best regards,
Q.



---------------------------------------


#include <pwd.h>
#include <grp.h>
#include <time.h>
#include <stdio.h>
#include <string.h>
#include <utime.h>
#include <unistd.h>
#include <stdlib.h>
#include <sys/time.h>


//#define BUG1
//#define BUG2


static void s_GetPwUid(uid_t uid)
{
    const struct passwd* pwd = getpwuid(uid);
    if (pwd) {
        printf("pw_name   = (%p)%s\n"
                "pw_passwd = (%p)%s\n"
                "pw_uid    = %u\n"
                "pw_gid    = %u\n"
                "pw_gecos  = (%p)%s\n"
                "pw_dir    = (%p)%s\n"
                "pw_shell  = (%p)%s\n\n",
                pwd->pw_name,   pwd->pw_name   ? pwd->pw_name   : "NULL",
                pwd->pw_passwd, pwd->pw_passwd ? pwd->pw_passwd : "NULL",
                (unsigned int) pwd->pw_uid,
                (unsigned int) pwd->pw_gid,
                pwd->pw_gecos,  pwd->pw_gecos  ? pwd->pw_gecos  : "NULL",
                pwd->pw_dir,    pwd->pw_dir    ? pwd->pw_dir    : "NULL",
                pwd->pw_shell, pwd->pw_shell   ? pwd->pw_shell  : "NULL");
    } else {
      printf("pwd = NULL\n\n");
    }
}


int main(void)
{
    s_GetPwUid(-1);

#ifdef BUG1
    {
    time_t t;
    struct timeval tv[2];
    sleep(2);

    t = time(0);
    memset(tv, 0, sizeof(tv));
    tv[0].tv_sec = t;
    tv[1].tv_sec = t;
    utimes("/etc/passwd", tv);

    s_GetPwUid(-1);
    }
#endif

#ifdef BUG2
    if (fork())
       return 0;

    s_GetPwUid(-1);
#endif

    return 0;
}

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Re: Two problems getting user and group info from /etc/{passwd,group}

[Corinna Vinschen]

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On Apr 11 13:41, q q wrote:
> 
> 
> Dear Cygwin developers,
> 
> Can you please take a look? - We came across a couple problems (times two, because they're identical for /etc/group as well):
> [...]

Well, if this isn't bad timing, I don't know what is.  In fact, the code
in question is not in CVS HEAD anymore, because I've turned everything
upside down to support fetching passwd and group information from SAM
and AD, without requiring /etc/passwd and /etc/group files.

I would like to suggest that you make yourself familiar with the changes
and try the latest developer snapshots from http://cygwin.com/snapshots/

For the impact of the changes, please see the information given in the
thread starting at http://cygwin.com/ml/cygwin/2014-02/threads.html#00306,
and especially the updated documentation attached to the mail
http://cygwin.com/ml/cygwin/2014-04/msg00248.html


HTH,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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