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 47ad2e83da91aafd22b24523edd1c49892742164..d138b6a0d274a1c4a1dd8f54656cefc7bc247433 100644 (file)
--- a/src/backend/catalog/dependency.c
+++ b/src/backend/catalog/dependency.c
@@ -910,6 +910,10 @@ 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
@@ -933,23 +937,28 @@ 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 a24e2cefa06d98d4de31a01d1140ed8e906046ae..ff7a1eb82470ac5b5f7121cbcda5bd1dfdaa9a5b 100644 (file)
--- a/src/backend/catalog/pg_shdepend.c
+++ b/src/backend/catalog/pg_shdepend.c
@@ -1113,6 +1113,12 @@ 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');