Avoid crash in rare case of concurrent DROP

alvherre · alvherre · commit 58b600f64bfb · 2021-11-05T12:29:34.000-03:00
When a role being dropped contains is referenced by catalog objects that are concurrently also being dropped, a crash can result while trying to construct the string that describes the objects. Suppress that by ignoring objects whose descriptions are returned as NULL. The majority of relevant codesites were already cautious about this already; we had just missed a couple. This is an old bug, so backpatch all the way back. Reported-by: Alexander Lakhin <exclusion@gmail.com> Discussion: https://postgr.es/m/17126-21887f04508cb5c8@postgresql.org
diff --git a/src/backend/catalog/dependency.c b/src/backend/catalog/dependency.c
@@ -902,6 +902,10 @@ reportDependentObjects(const ObjectAddresses *targetObjects,
 
 		objDesc = getObjectDescription(obj);
 
+		/* An object being dropped concurrently doesn't need to be reported */
+		if (objDesc == NULL)
+			continue;
+
 		/*
 		 * If, at any stage of the recursive search, we reached the object via
 		 * an AUTO, INTERNAL, or EXTENSION dependency, then it's okay to
@@ -925,23 +929,28 @@ reportDependentObjects(const ObjectAddresses *targetObjects,
 		{
 			char	   *otherDesc = getObjectDescription(&extra->dependee);
 
-			if (numReportedClient < MAX_REPORTED_DEPS)
+			if (otherDesc)
 			{
+				if (numReportedClient < MAX_REPORTED_DEPS)
+				{
+					/* separate entries with a newline */
+					if (clientdetail.len != 0)
+						appendStringInfoChar(&clientdetail, '\n');
+					appendStringInfo(&clientdetail, _("%s depends on %s"),
+									 objDesc, otherDesc);
+					numReportedClient++;
+				}
+				else
+					numNotReportedClient++;
 				/* separate entries with a newline */
-				if (clientdetail.len != 0)
-					appendStringInfoChar(&clientdetail, '\n');
-				appendStringInfo(&clientdetail, _("%s depends on %s"),
+				if (logdetail.len != 0)
+					appendStringInfoChar(&logdetail, '\n');
+				appendStringInfo(&logdetail, _("%s depends on %s"),
 								 objDesc, otherDesc);
-				numReportedClient++;
+				pfree(otherDesc);
 			}
 			else
 				numNotReportedClient++;
-			/* separate entries with a newline */
-			if (logdetail.len != 0)
-				appendStringInfoChar(&logdetail, '\n');
-			appendStringInfo(&logdetail, _("%s depends on %s"),
-							 objDesc, otherDesc);
-			pfree(otherDesc);
 			ok = false;
 		}
 		else
diff --git a/src/backend/catalog/pg_shdepend.c b/src/backend/catalog/pg_shdepend.c
@@ -1065,6 +1065,12 @@ storeObjectDescription(StringInfo descs,
 {
 	char	   *objdesc = getObjectDescription(object);
 
+	/*
+	 * An object being dropped concurrently doesn't need to be reported.
+	 */
+	if (objdesc == NULL)
+		return;
+
 	/* separate entries with a newline */
 	if (descs->len != 0)
 		appendStringInfoChar(descs, '\n');
