Properly determine length for on-disk TOAST values

In detoast_attr_slice, VARSIZE_ANY was used to compute compressed length
of on-disk TOAST values. That's incorrect, because the varlena value may
be just a TOAST pointer, producing either bogus value or crashing.

This is likely why the code was crashing on big-endian machines before
540f31680913 replaced the VARSIZE with VARSIZE_ANY, which however only
masked the issue.

Reported-by: Rushabh Lathia
Discussion: https://postgr.es/m/CAL-OGkthU9Gs7TZchf5OWaL-Gsi=hXqufTxKv9qpNG73d5na_g@mail.gmail.com

diff --git a/src/backend/access/common/detoast.c b/src/backend/access/common/detoast.c
index f752ac7bbc917c1220eb764da6378a550d493b9d..8c89fc2a558bd6e199f92da55dec617fef9de403 100644 (file)
--- a/src/backend/access/common/detoast.c
+++ b/src/backend/access/common/detoast.c
@@ -233,7 +233,7 @@ detoast_attr_slice(struct varlena *attr,
                         * of a given length (after decompression).
                         */
                        max_size = pglz_maximum_compressed_size(sliceoffset + slicelength,
-                                                                                                       TOAST_COMPRESS_SIZE(attr));
+                                                                                                       toast_pointer.va_extsize);
 
                        /*
                         * Fetch enough compressed slices (compressed marker will get set