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Prevent PL/Tcl from loading the "unknown" module from pltcl_modules unless

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that is a regular table or view owned by a superuser.  This prevents a
trojan horse attack whereby any unprivileged SQL user could create such a
table and insert code into it that would then get executed in other users'
sessions whenever they call pltcl functions.

Worse yet, because the code was automatically loaded into both the "normal"
and "safe" interpreters at first use, the attacker could execute unrestricted
Tcl code in the "normal" interpreter without there being any pltclu functions
anywhere, or indeed anyone else using pltcl at all: installing pltcl is
sufficient to open the hole.  Change the initialization logic so that the
"unknown" code is only loaded into an interpreter when the interpreter is
first really used.  (That doesn't add any additional security in this
particular context, but it seems a prudent change, and anyway the former
behavior violated the principle of least astonishment.)

Security: CVE-2010-1170
This commit is contained in:
Tom Lane
2010-05-13 18:29:31 +00:00
parent 64a42a2af8
commit 650d950efc
2 changed files with 135 additions and 67 deletions
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14
doc/src/sgml/pltcl.sgml
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@ -1,4 +1,4 @@
<!-- $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.42.2.1 2007/01/30 22:29:40 momjian Exp $ -->
<!-- $PostgreSQL: pgsql/doc/src/sgml/pltcl.sgml,v 2.42.2.2 2010/05/13 18:29:31 tgl Exp $ -->
<chapter id="pltcl">
<title>PL/Tcl - Tcl Procedural Language</title>
@ -690,8 +690,10 @@ CREATE TRIGGER trig_mytab_modcount BEFORE INSERT OR UPDATE ON mytab
It recognizes a special table, <literal>pltcl_modules</>, which
is presumed to contain modules of Tcl code. If this table
exists, the module <literal>unknown</> is fetched from the table
and loaded into the Tcl interpreter immediately after creating
the interpreter.
and loaded into the Tcl interpreter immediately before the first
execution of a PL/Tcl function in a database session. (This
happens separately for PL/Tcl and PL/TclU, if both are used,
because separate interpreters are used for the two languages.)
</para>
<para>
While the <literal>unknown</> module could actually contain any
@ -718,7 +720,11 @@ CREATE TRIGGER trig_mytab_modcount BEFORE INSERT OR UPDATE ON mytab
<para>
The tables <literal>pltcl_modules</> and <literal>pltcl_modfuncs</>
must be readable by all, but it is wise to make them owned and
writable only by the database administrator.
writable only by the database administrator. As a security
precaution, PL/Tcl will ignore <literal>pltcl_modules</> (and thus,
not attempt to load the <literal>unknown</> module) unless it is
owned by a superuser. But update privileges on this table can be
granted to other users, if you trust them sufficiently.
</para>
</sect1>