Defend against crash while processing Describe Statement or Describe Portal

messages, when client attempts to execute these outside a transaction (start
one) or in a failed transaction (reject message, except for COMMIT/ROLLBACK
statements which we can handle).  Per report from Francisco Figueiredo Jr.

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 2a6cbd77f0a169b3de0ce2e8b32f726f46072da2..c1323f5511b99a9dfaead0d83d4a50b5889576ee 100644 (file)
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -10,7 +10,7 @@
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.36 2005/01/01 05:43:06 momjian Exp $
+ *   $PostgreSQL: pgsql/src/backend/commands/prepare.c,v 1.36.4.1 2005/12/14 17:06:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -441,6 +441,30 @@ FetchPreparedStatementResultDesc(PreparedStatement *stmt)
    return NULL;
 }
 
+/*
+ * Given a prepared statement, determine whether it will return tuples.
+ *
+ * Note: this is used rather than just testing the result of
+ * FetchPreparedStatementResultDesc() because that routine can fail if
+ * invoked in an aborted transaction.  This one is safe to use in any
+ * context.  Be sure to keep the two routines in sync!
+ */
+bool
+PreparedStatementReturnsTuples(PreparedStatement *stmt)
+{
+   switch (ChoosePortalStrategy(stmt->query_list))
+   {
+       case PORTAL_ONE_SELECT:
+       case PORTAL_UTIL_SELECT:
+           return true;
+
+       case PORTAL_MULTI_QUERY:
+           /* will not return tuples */
+           break;
+   }
+   return false;
+}
+
 /*
  * Implements the 'DEALLOCATE' utility statement: deletes the
  * specified plan from storage.

diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 4dc74c8d86a8d99d39376cd52bec405c47397ed4..b166e7d9b8ec96473afca58ad37b0e8e43e498b7 100644 (file)
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.440.4.4 2005/11/10 00:31:49 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.440.4.5 2005/12/14 17:06:51 tgl Exp $
  *
  * NOTES
  *   this is the "main" module of the postgres backend and
@@ -1732,6 +1732,15 @@ exec_describe_statement_message(const char *stmt_name)
    ListCell   *l;
    StringInfoData buf;
 
+   /*
+    * Start up a transaction command. (Note that this will normally change
+    * current memory context.) Nothing happens if we are already in one.
+    */
+   start_xact_command();
+
+   /* Switch back to message context */
+   MemoryContextSwitchTo(MessageContext);
+
    /* Find prepared statement */
    if (stmt_name[0] != '\0')
        pstmt = FetchPreparedStatement(stmt_name, true);
@@ -1745,6 +1754,22 @@ exec_describe_statement_message(const char *stmt_name)
                   errmsg("unnamed prepared statement does not exist")));
    }
 
+   /*
+    * If we are in aborted transaction state, we can't safely create a result
+    * tupledesc, because that needs catalog accesses.  Hence, refuse to
+    * Describe statements that return data.  (We shouldn't just refuse all
+    * Describes, since that might break the ability of some clients to issue
+    * COMMIT or ROLLBACK commands, if they use code that blindly Describes
+    * whatever it does.)  We can Describe parameters without doing anything
+    * dangerous, so we don't restrict that.
+    */
+   if (IsAbortedTransactionBlockState() &&
+       PreparedStatementReturnsTuples(pstmt))
+       ereport(ERROR,
+               (errcode(ERRCODE_IN_FAILED_SQL_TRANSACTION),
+                errmsg("current transaction is aborted, "
+                       "commands ignored until end of transaction block")));
+
    if (whereToSendOutput != Remote)
        return;                 /* can't actually do anything... */
 
@@ -1791,12 +1816,36 @@ exec_describe_portal_message(const char *portal_name)
 {
    Portal      portal;
 
+   /*
+    * Start up a transaction command. (Note that this will normally change
+    * current memory context.) Nothing happens if we are already in one.
+    */
+   start_xact_command();
+
+   /* Switch back to message context */
+   MemoryContextSwitchTo(MessageContext);
+
    portal = GetPortalByName(portal_name);
    if (!PortalIsValid(portal))
        ereport(ERROR,
                (errcode(ERRCODE_UNDEFINED_CURSOR),
                 errmsg("portal \"%s\" does not exist", portal_name)));
 
+   /*
+    * If we are in aborted transaction state, we can't run
+    * SendRowDescriptionMessage(), because that needs catalog accesses.
+    * Hence, refuse to Describe portals that return data.  (We shouldn't just
+    * refuse all Describes, since that might break the ability of some
+    * clients to issue COMMIT or ROLLBACK commands, if they use code that
+    * blindly Describes whatever it does.)
+    */
+   if (IsAbortedTransactionBlockState() &&
+       portal->tupDesc)
+       ereport(ERROR,
+               (errcode(ERRCODE_IN_FAILED_SQL_TRANSACTION),
+                errmsg("current transaction is aborted, "
+                       "commands ignored until end of transaction block")));
+
    if (whereToSendOutput != Remote)
        return;                 /* can't actually do anything... */
 

diff --git a/src/include/commands/prepare.h b/src/include/commands/prepare.h
index 4a8cde52354d5be670512d519c2436b7725f8889..6582beb17140a85489c1fa52d0d30ed0f27eeea9 100644 (file)
--- a/src/include/commands/prepare.h
+++ b/src/include/commands/prepare.h
@@ -6,7 +6,7 @@
  *
  * Copyright (c) 2002-2005, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/include/commands/prepare.h,v 1.13 2005/01/01 05:43:09 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/commands/prepare.h,v 1.13.4.1 2005/12/14 17:06:51 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -59,5 +59,6 @@ extern PreparedStatement *FetchPreparedStatement(const char *stmt_name,
 extern void DropPreparedStatement(const char *stmt_name, bool showError);
 extern List *FetchPreparedStatementParams(const char *stmt_name);
 extern TupleDesc FetchPreparedStatementResultDesc(PreparedStatement *stmt);
+extern bool PreparedStatementReturnsTuples(PreparedStatement *stmt);
 
 #endif   /* PREPARE_H */