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 4b80e713a1445e976fffb7220bf27b073baa4ded..ef16e6ba133bbda916a01c4c4b3101e587a424b7 100644 (file)
--- 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
index a6286666978746729122897b0c8b31ba101e97db..6964d439ef70c296481e3154be42b7cf136f124a 100644 (file)
--- 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');