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 9f8eb1a37fda36ebe7394015750147d1444f899e..fe9c714257fbd660de75a08c344206c6ae093d33 100644 (file)
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -1094,6 +1094,10 @@ reportDependentObjects(const ObjectAddresses *targetObjects,
 
        objDesc = getObjectDescription(obj, false);
 
+       /* 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
@@ -1119,23 +1123,28 @@ reportDependentObjects(const ObjectAddresses *targetObjects,
            char       *otherDesc = getObjectDescription(&extra->dependee,
                                                         false);
 
-           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 8453d8fefd7251f86b21f58c16855f9927886189..9ea42f805fad503245f317dafedcc57cbbfcdd5d 100644 (file)
--- a/src/backend/catalog/pg_shdepend.c
+++ b/src/backend/catalog/pg_shdepend.c
@@ -1234,6 +1234,12 @@ storeObjectDescription(StringInfo descs,
 {
    char       *objdesc = getObjectDescription(object, false);
 
+   /*
+    * 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');