lib/, src/, configure.ac: Use utmpx instead of utmp

[alejandro-colomar]

utmpx is specified by POSIX as an XSI extension. That's more portable than utmp, which is unavailable for example in musl libc. The manual page specifies that in Linux (but it probably means in glibc), utmp and utmpx (and the functions that use them) are identical, so this commit shouldn't affect glibc systems.

Assume utmpx is always present.

Also, if utmpx is present, POSIX guarantees that some members exist:

• ut_user
• ut_id
• ut_line
• ut_pid
• ut_type
• ut_tv

So, rely on them unconditionally.

Fixes: 170b76c ("Disable utmpx permanently")
Closes: #945
Reported-by: @firasuke
Reported-by: @awilfox

[alejandro-colomar]

I suggest reviewing with

git show --color-words=. --patience

[alejandro-colomar]

v1b changes:

• tfix subject line

$ git range-diff shadow/master gh/utmp utmp 
1:  24522aa0 ! 1:  af1b9f4d lib/, src. configure.ac: Use utmpx instead of utmp
    @@ Metadata
     Author: Alejandro Colomar <alx@kernel.org>
     
      ## Commit message ##
    -    lib/, src. configure.ac: Use utmpx instead of utmp
    +    lib/, src/, configure.ac: Use utmpx instead of utmp
     
         utmpx is specified by POSIX as an XSI extension.  That's more portable
         than utmp, which is unavailable for example in musl libc.  The manual

[firasuke]

I will have to test this, though I don't see any changes being made to login.c?

[alejandro-colomar]

I will have to test this,

Please, and thanks!

though I don't see any changes being made to login.c?

No, the changes are in the library code. login.c doesn't seem to be using utmp directly.

$ grep -rn utmp src/login.c
689:	 * information coming from login or from the caller (e.g. no utmp)
1178:	 * The utmp entry needs to be updated to indicate the new status
1181:	err = update_utmp (username, tty, hostname);
1183:		SYSLOG ((LOG_WARN, "Unable to update utmp entry for %s", username));

@awilfox , would you mind testing it too for your distribution?

[alejandro-colomar]

v2 changes:

• s/endutent/endutxent/

$ git range-diff shadow/master gh/utmp utmp 
1:  af1b9f4d ! 1:  595c6909 lib/, src/, configure.ac: Use utmpx instead of utmp
    @@ lib/utmp.c: err_close:
                memcpy (ret, ut, sizeof (*ret));
        }
      
    -@@ lib/utmp.c: static
    +-  endutent ();
    ++  endutxent();
    + 
        return ret;
      }
      
    @@ src/logoutd.c: int main (int argc, char **argv)
                        if (ut->ut_type != USER_PROCESS) {
                                continue;
                        }
    +@@ src/logoutd.c: int main (int argc, char **argv)
    +                   exit (EXIT_SUCCESS);
    +           }
    + 
    +-          endutent ();
    ++          endutxent();
    + 
    + #ifndef DEBUG
    +           sleep (60);

[alejandro-colomar]

v3 changes:

• Reduce scope of variable, to silence a warning.

$ git range-diff shadow/master gh/utmp utmp 
1:  595c6909 = 1:  595c6909 lib/, src/, configure.ac: Use utmpx instead of utmp
-:  -------- > 2:  e9255d0d lib/utmp.c: get_session_host(): Reduce scope of variable

[firasuke]

Ok I tried the utmp branch and I am receiving the following error when running ./configure:

...
checking for library containing readpassphrase... no
configure: error: readpassphrase() is missing, either from libc or libbsd
...

[alejandro-colomar]

Ok I tried the utmp branch and I am receiving the following error when running ./configure:

...
checking for library containing readpassphrase... no
configure: error: readpassphrase() is missing, either from libc or libbsd
...

You need to either install libbsd, or autogen with --without-libbsd. I recommend using libbsd, but some systems, like Fedora, don't want to have libbsd in their core packages, so they use --without-libbsd.

See:

• shadow/share/containers/fedora.dockerfile

  Line 13 in 4d139ca

  --without-libpam --enable-shared --without-libbsd \

• shadow/share/containers/debian.dockerfile

  Line 12 in 4d139ca

  RUN apt-get install libltdl-dev libbsd-dev libcmocka-dev pkgconf -y

• shadow/share/containers/alpine.dockerfile

  Line 5 in 4d139ca

  RUN apk add autoconf automake build-base byacc cmocka-dev expect gettext-dev \

[firasuke]

Ok I tried the utmp branch and I am receiving the following error when running ./configure:

...
checking for library containing readpassphrase... no
configure: error: readpassphrase() is missing, either from libc or libbsd
...

You need to either install libbsd, or autogen with --without-libbsd. I recommend using libbsd, but some systems, like Fedora, don't want to have libbsd in their core packages, so they use --without-libbsd.

See:

* https://github.com/shadow-maint/shadow/blob/4d139ca466820b9a5fe8f75b9a0bee6a922d906a/share/containers/fedora.dockerfile#L13

* https://github.com/shadow-maint/shadow/blob/4d139ca466820b9a5fe8f75b9a0bee6a922d906a/share/containers/debian.dockerfile#L12

* https://github.com/shadow-maint/shadow/blob/4d139ca466820b9a5fe8f75b9a0bee6a922d906a/share/containers/alpine.dockerfile#L5

Silly me, I already had that disabled, but perhaps dropped it after downgrading. Thanks for the reminder!

[firasuke]

And I can confirm it is working as intended!

[alejandro-colomar]

v4 changes:

• Tested-by: @firasuke
• Don't use UT_LINESIZE with struct utmpx. (fixes CI dist-build)

$ git range-diff shadow/master gh/utmp utmp 
1:  595c6909 ! 1:  1d755860 lib/, src/, configure.ac: Use utmpx instead of utmp
    @@ Commit message
         Closes: <https://github.com/shadow-maint/shadow/issues/945>
         Reported-by: Firas Khalil Khana <firasuke@gmail.com>
         Reported-by: "A. Wilfox" <https://github.com/awilfox>
    +    Tested-by: Firas Khalil Khana <firasuke@gmail.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## configure.ac ##
2:  e9255d0d ! 2:  05e9aeb7 lib/utmp.c: get_session_host(): Reduce scope of variable
    @@ Commit message
     
         This silences a warning about an unused variable.
     
    +    Tested-by: Firas Khalil Khana <firasuke@gmail.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## lib/utmp.c ##
-:  -------- > 3:  4628615a lib/sizeof.h: memberof(): Add macro
-:  -------- > 4:  64d45e98 lib/utmp.c: Replace UT_LINESIZE by a NITEMS() calculation

[ikerexxe]

The code looks good!

[alejandro-colomar]

v4b changes:

• Reviewed-by: @ikerexxe

$ git range-diff shadow/master gh/utmp utmp 
1:  1d755860 ! 1:  7e295795 lib/, src/, configure.ac: Use utmpx instead of utmp
    @@ Commit message
         Reported-by: Firas Khalil Khana <firasuke@gmail.com>
         Reported-by: "A. Wilfox" <https://github.com/awilfox>
         Tested-by: Firas Khalil Khana <firasuke@gmail.com>
    +    Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## configure.ac ##
2:  05e9aeb7 ! 2:  661ce052 lib/utmp.c: get_session_host(): Reduce scope of variable
    @@ Commit message
         This silences a warning about an unused variable.
     
         Tested-by: Firas Khalil Khana <firasuke@gmail.com>
    +    Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## lib/utmp.c ##
3:  4628615a ! 3:  b962685e lib/sizeof.h: memberof(): Add macro
    @@ Commit message
         This macro is useful to get the size of a member of a structure
         without having a variable of that type.
     
    +    Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## lib/sizeof.h ##
4:  64d45e98 ! 4:  7e72c19c lib/utmp.c: Replace UT_LINESIZE by a NITEMS() calculation
    @@ Commit message
         size.  Therefore, we need to get the number of elements in
         the array with NITEMS().
     
    +    Reviewed-by: Iker Pedrosa <ipedrosa@redhat.com>
         Signed-off-by: Alejandro Colomar <alx@kernel.org>
     
      ## lib/utmp.c ##