Re: SECURITY: psql allows symlink games in /tmp - Mailing list pgsql-hackers

Looks like what I would have done if I knew C.

The only issue remaining is a policy issue as to if psql should call an
editor in /tmp at all, considering the issues raised bye the recent joe
vulnerability, ie can we trust the editor not to do a crazy thing, like
not creating a similarly predictable backup-file name etc.  It should at
least be documented so that a more parinoid sys-admin can make sure that
users use a private TMPDIR.

Thanks for the quick response,

Andrew Bartlett
abartlet@pcug.org.au

Bruce Momjian wrote:
> 
> Thanks for the pointer.  Here is a diff to fix the problem.  How does it
> look to you?
> 
> > This code in psql/command.c allows *any* system user to place a
> > predictably named symbolic link in /tmp and use it to alter/destroy
> > files owned by the user running psql. (tested - postgresql 7.0.2).
> >
> > All the information a potential attacker would need are available via a
> > simple 'ps'.
> >
> > It might (untested) also allow an another user to exploit the race
> > between the closing of the file by the editor and the re-reading of its
> > contents to execute arbitrary SQL commands.
> >
> > IMHO these files, if they must be created in /tmp should at least be
> > created O_EXCL, but there are still editor vulnerabilities with opening
> > any files in a world writeable directory (see recent joe Vulnerability:
> > http://lwn.net/2000/1123/a/sec-joe.php3)
> >
> > My system is RedHat 6.2 on an i686, with Postgresql 7.0.2 but the same
> > code currently exists in CVS (or at least CVS-web).
> >
> > I am not subscribed to this list, so please CC me for replies.  (Also
> > tell me if there is a more appropriate forum for this, but
> > www.postgresql.org doesn't have a listed security issue address).
> > --
> > Andrew Bartlett
> > abartlet@pcug.org.au
> >
> 
> --
>   Bruce Momjian                        |  http://candle.pha.pa.us
>   pgman@candle.pha.pa.us               |  (610) 853-3000
>   +  If your life is a hard drive,     |  830 Blythe Avenue
>   +  Christ can be your backup.        |  Drexel Hill, Pennsylvania 19026
> 
>   ------------------------------------------------------------------------
> ? config.log
> ? config.cache
> ? config.status
> ? GNUmakefile
> ? src/Makefile.custom
> ? src/GNUmakefile
> ? src/Makefile.global
> ? src/log
> ? src/crtags
> ? src/backend/postgres
> ? src/backend/catalog/global.description
> ? src/backend/catalog/global.bki
> ? src/backend/catalog/template1.bki
> ? src/backend/catalog/template1.description
> ? src/backend/port/Makefile
> ? src/bin/initdb/initdb
> ? src/bin/initlocation/initlocation
> ? src/bin/ipcclean/ipcclean
> ? src/bin/pg_config/pg_config
> ? src/bin/pg_ctl/pg_ctl
> ? src/bin/pg_dump/pg_dump
> ? src/bin/pg_dump/pg_restore
> ? src/bin/pg_dump/pg_dumpall
> ? src/bin/pg_id/pg_id
> ? src/bin/pg_passwd/pg_passwd
> ? src/bin/pgaccess/pgaccess
> ? src/bin/pgtclsh/Makefile.tkdefs
> ? src/bin/pgtclsh/Makefile.tcldefs
> ? src/bin/pgtclsh/pgtclsh
> ? src/bin/pgtclsh/pgtksh
> ? src/bin/psql/psql
> ? src/bin/scripts/createlang
> ? src/include/config.h
> ? src/include/stamp-h
> ? src/interfaces/ecpg/lib/libecpg.so.3.2.0
> ? src/interfaces/ecpg/preproc/ecpg
> ? src/interfaces/libpgeasy/libpgeasy.so.2.1
> ? src/interfaces/libpgtcl/libpgtcl.so.2.1
> ? src/interfaces/libpq/libpq.so.2.1
> ? src/interfaces/perl5/blib
> ? src/interfaces/perl5/Makefile
> ? src/interfaces/perl5/pm_to_blib
> ? src/interfaces/perl5/Pg.c
> ? src/interfaces/perl5/Pg.bs
> ? src/pl/plperl/blib
> ? src/pl/plperl/Makefile
> ? src/pl/plperl/pm_to_blib
> ? src/pl/plperl/SPI.c
> ? src/pl/plperl/plperl.bs
> ? src/pl/plpgsql/src/libplpgsql.so.1.0
> ? src/pl/tcl/Makefile.tcldefs
> Index: src/bin/psql/command.c
> ===================================================================
> RCS file: /home/projects/pgsql/cvsroot/pgsql/src/bin/psql/command.c,v
> retrieving revision 1.38
> diff -c -r1.38 command.c
> *** src/bin/psql/command.c      2000/11/13 23:37:53     1.38
> --- src/bin/psql/command.c      2000/11/25 06:18:33
> ***************
> *** 13,19 ****
>   #include <ctype.h>
>   #ifndef WIN32
>   #include <sys/types.h>                        /* for umask() */
> ! #include <sys/stat.h>                 /* for umask(), stat() */
>   #include <unistd.h>                           /* for geteuid(), getpid(), stat() */
>   #else
>   #include <win32.h>
> --- 13,20 ----
>   #include <ctype.h>
>   #ifndef WIN32
>   #include <sys/types.h>                        /* for umask() */
> ! #include <sys/stat.h>                 /* for stat() */
> ! #include <fcntl.h>                            /* open() flags */
>   #include <unistd.h>                           /* for geteuid(), getpid(), stat() */
>   #else
>   #include <win32.h>
> ***************
> *** 1397,1403 ****
>         FILE       *stream;
>         const char *fname;
>         bool            error = false;
> !
>   #ifndef WIN32
>         struct stat before,
>                                 after;
> --- 1398,1405 ----
>         FILE       *stream;
>         const char *fname;
>         bool            error = false;
> !       int                     fd;
> !
>   #ifndef WIN32
>         struct stat before,
>                                 after;
> ***************
> *** 1411,1417 ****
>         {
>                 /* make a temp file to edit */
>   #ifndef WIN32
> -               mode_t          oldumask;
>                 const char *tmpdirenv = getenv("TMPDIR");
> 
>                 sprintf(fnametmp, "%s/psql.edit.%ld.%ld",
> --- 1413,1418 ----
> ***************
> *** 1422,1436 ****
>   #endif
>                 fname = (const char *) fnametmp;
> 
> ! #ifndef WIN32
> !               oldumask = umask(0177);
> ! #endif
> !               stream = fopen(fname, "w");
> ! #ifndef WIN32
> !               umask(oldumask);
> ! #endif
> 
> !               if (!stream)
>                 {
>                         psql_error("couldn't open temp file %s: %s\n", fname, strerror(errno));
>                         error = true;
> --- 1423,1433 ----
>   #endif
>                 fname = (const char *) fnametmp;
> 
> !               fd = open(fname, O_WRONLY|O_CREAT|O_EXCL, 0600);
> !               if (fd != -1)
> !                       stream = fdopen(fd, "w");
> 
> !               if (fd == -1 || !stream)
>                 {
>                         psql_error("couldn't open temp file %s: %s\n", fname, strerror(errno));
>                         error = true;

-- 
Andrew Bartlett
abartlet@pcug.org.au