Ignore attempts to \gset into specially treated variables.

If an interactive psql session used \gset when querying a compromised
server, the attacker could execute arbitrary code as the operating
system account running psql.  Using a prefix not found among specially
treated variables, e.g. every lowercase string, precluded the attack.
Fix by issuing a warning and setting no variable for the column in
question.  Users wanting the old behavior can use a prefix and then a
meta-command like "\set HISTSIZE :prefix_HISTSIZE".  Back-patch to 9.5
(all supported versions).

Reviewed by Robert Haas.  Reported by Nick Cleaton.

Security: CVE-2020-25696

diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index ff673665d869e52db3c6008e0d905f28177082d3..dfbc22970f83165aa6bb16b9e3f885496ca524b4 100644 (file)
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -786,6 +786,13 @@ StoreQueryTuple(const PGresult *result)
            /* concatenate prefix and column name */
            varname = psprintf("%s%s", pset.gset_prefix, colname);
 
+           if (VariableHasHook(pset.vars, varname))
+           {
+               pg_log_warning("attempt to \\gset into specially treated variable \"%s\" ignored",
+                              varname);
+               continue;
+           }
+
            if (!PQgetisnull(result, 0, i))
                value = PQgetvalue(result, 0, i);
            else

diff --git a/src/bin/psql/variables.c b/src/bin/psql/variables.c
index 52aa5e5f1645b245365893cfd39545fd2d21a06d..84349fc753f02b82dd4d7e706295eed9cf0415e6 100644 (file)
--- a/src/bin/psql/variables.c
+++ b/src/bin/psql/variables.c
@@ -360,6 +360,32 @@ SetVariableHooks(VariableSpace space, const char *name,
        (void) (*ahook) (current->value);
 }
 
+/*
+ * Return true iff the named variable has substitute and/or assign hook
+ * functions.
+ */
+bool
+VariableHasHook(VariableSpace space, const char *name)
+{
+   struct _variable *current;
+
+   Assert(space);
+   Assert(name);
+
+   for (current = space->next; current; current = current->next)
+   {
+       int         cmp = strcmp(current->name, name);
+
+       if (cmp == 0)
+           return (current->substitute_hook != NULL ||
+                   current->assign_hook != NULL);
+       if (cmp > 0)
+           break;              /* it's not there */
+   }
+
+   return false;
+}
+
 /*
  * Convenience function to set a variable's value to "on".
  */

diff --git a/src/bin/psql/variables.h b/src/bin/psql/variables.h
index ab5e51f20b5b4e58da2a5ac76873de6ddc3b23e4..b932472021a742c3137d1044361ddb60b2c9570c 100644 (file)
--- a/src/bin/psql/variables.h
+++ b/src/bin/psql/variables.h
@@ -90,6 +90,7 @@ bool      DeleteVariable(VariableSpace space, const char *name);
 void       SetVariableHooks(VariableSpace space, const char *name,
                             VariableSubstituteHook shook,
                             VariableAssignHook ahook);
+bool       VariableHasHook(VariableSpace space, const char *name);
 
 void       PsqlVarEnumError(const char *name, const char *value, const char *suggestions);
 

diff --git a/src/test/regress/expected/psql.out b/src/test/regress/expected/psql.out
index daac0ff49d6e08e0839bd1b07ce3169c854cedef..7204fdb0b439c3ce7c824d6209db122df511b4d7 100644 (file)
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -106,6 +106,10 @@ select 10 as test01, 20 as test02, 'Hello' as test03 \gset pref01_
 select 10 as "bad name"
 \gset
 invalid variable name: "bad name"
+select 97 as "EOF", 'ok' as _foo \gset IGNORE
+attempt to \gset into specially treated variable "IGNOREEOF" ignored
+\echo :IGNORE_foo :IGNOREEOF
+ok 0
 -- multiple backslash commands in one line
 select 1 as x, 2 as y \gset pref01_ \\ \echo :pref01_x
 1

diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
index 47b28d2a0763927b8e4383f651983929717ead44..537d5332aa90c0a0ce40b34550f5e687e5abcd9a 100644 (file)
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -55,6 +55,9 @@ select 10 as test01, 20 as test02, 'Hello' as test03 \gset pref01_
 select 10 as "bad name"
 \gset
 
+select 97 as "EOF", 'ok' as _foo \gset IGNORE
+\echo :IGNORE_foo :IGNOREEOF
+
 -- multiple backslash commands in one line
 select 1 as x, 2 as y \gset pref01_ \\ \echo :pref01_x
 select 3 as x, 4 as y \gset pref01_ \echo :pref01_x \echo :pref01_y