Add some simple defenses against null fields in pg_largeobject, and add

comments noting that there's an alignment assumption now that the data
field could be in 1-byte-header format.  Per discussion with Greg Stark.

diff --git a/src/backend/storage/large_object/inv_api.c b/src/backend/storage/large_object/inv_api.c
index ea98ab2952069a6224e375a15e5e0e596ae30386..77b756cabb99339b2500c5311f1bee33dc5f081c 100644 (file)
--- a/src/backend/storage/large_object/inv_api.c
+++ b/src/backend/storage/large_object/inv_api.c
@@ -5,6 +5,13 @@
  *   contains the user-level large object application interface routines.
  *
  *
+ * Note: we access pg_largeobject.data using its C struct declaration.
+ * This is safe because it immediately follows pageno which is an int4 field,
+ * and therefore the data field will always be 4-byte aligned, even if it
+ * is in the short 1-byte-header format.  We have to detoast it since it's
+ * quite likely to be in compressed or short format.  We also need to check
+ * for NULLs, since initdb will mark loid and pageno but not data as NOT NULL.
+ *
  * Note: many of these routines leak memory in CurrentMemoryContext, as indeed
  * does most of the backend code.  We expect that CurrentMemoryContext will
  * be a short-lived context.  Data that must persist across function calls
@@ -17,7 +24,7 @@
  *
  *
  * IDENTIFICATION
- *   $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.124 2007/04/06 04:21:42 tgl Exp $
+ *   $PostgreSQL: pgsql/src/backend/storage/large_object/inv_api.c,v 1.125 2007/06/12 19:46:24 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -330,8 +337,10 @@ inv_getsize(LargeObjectDesc *obj_desc)
        bool        pfreeit;
 
        found = true;
+       if (HeapTupleHasNulls(tuple))               /* paranoia */
+           elog(ERROR, "null field found in pg_largeobject");
        data = (Form_pg_largeobject) GETSTRUCT(tuple);
-       datafield = &(data->data);
+       datafield = &(data->data);          /* see note at top of file */
        pfreeit = false;
        if (VARATT_IS_EXTENDED(datafield))
        {
@@ -434,6 +443,8 @@ inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
        bytea      *datafield;
        bool        pfreeit;
 
+       if (HeapTupleHasNulls(tuple))               /* paranoia */
+           elog(ERROR, "null field found in pg_largeobject");
        data = (Form_pg_largeobject) GETSTRUCT(tuple);
 
        /*
@@ -457,7 +468,7 @@ inv_read(LargeObjectDesc *obj_desc, char *buf, int nbytes)
            off = (int) (obj_desc->offset - pageoff);
            Assert(off >= 0 && off < LOBLKSIZE);
 
-           datafield = &(data->data);
+           datafield = &(data->data);          /* see note at top of file */
            pfreeit = false;
            if (VARATT_IS_EXTENDED(datafield))
            {
@@ -558,6 +569,8 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
        {
            if ((oldtuple = index_getnext(sd, ForwardScanDirection)) != NULL)
            {
+               if (HeapTupleHasNulls(oldtuple))            /* paranoia */
+                   elog(ERROR, "null field found in pg_largeobject");
                olddata = (Form_pg_largeobject) GETSTRUCT(oldtuple);
                Assert(olddata->pageno >= pageno);
            }
@@ -575,7 +588,7 @@ inv_write(LargeObjectDesc *obj_desc, const char *buf, int nbytes)
             *
             * First, load old data into workbuf
             */
-           datafield = &(olddata->data);
+           datafield = &(olddata->data);       /* see note at top of file */
            pfreeit = false;
            if (VARATT_IS_EXTENDED(datafield))
            {
@@ -737,6 +750,8 @@ inv_truncate(LargeObjectDesc *obj_desc, int len)
    olddata = NULL;
    if ((oldtuple = index_getnext(sd, ForwardScanDirection)) != NULL)
    {
+       if (HeapTupleHasNulls(oldtuple))                /* paranoia */
+           elog(ERROR, "null field found in pg_largeobject");
        olddata = (Form_pg_largeobject) GETSTRUCT(oldtuple);
        Assert(olddata->pageno >= pageno);
    }
@@ -749,7 +764,7 @@ inv_truncate(LargeObjectDesc *obj_desc, int len)
    if (olddata != NULL && olddata->pageno == pageno)
    {
        /* First, load old data into workbuf */
-       bytea *datafield = &(olddata->data);
+       bytea *datafield = &(olddata->data);    /* see note at top of file */
        bool pfreeit = false;
        int pagelen;