Properly determine length for on-disk TOAST values

tvondra · tvondra · commit 2dc08bd6179d · 2019-11-16T03:07:11.000+01:00
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 540f316 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
@@ -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
