Avoid crash in rare case of concurrent DROP

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
index 038469c9a3a12dc9741460248a74d12b060e44a5..fda39726d499ba56a87238332752a500f69a1f72 100644 (file)
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -1108,6 +1108,10 @@ 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, PARTITION, or EXTENSION dependency, then it's
@@ -1132,23 +1136,28 @@ 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
index 076ba2d1afcdbcb5993f7418a02c5440d8bbdc2e..860f98238c6b209bae656ab5f2fcb9b8e684c027 100644 (file)
--- a/src/backend/catalog/pg_shdepend.c
+++ b/src/backend/catalog/pg_shdepend.c
@@ -1198,6 +1198,12 @@ 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');