pstore: fix potential logic issue in pstore read interface

1) in the calling of erst_read, the parameter of buffer size
maybe overflows and cause crash

2) the return value of erst_read should be checked more strictly

Signed-off-by: Chen Gong <gong.chen@linux.intel.com>
Signed-off-by: Tony Luck <tony.luck@intel.com>

drivers/acpi/apei/erst.c

@@ -1006,7 +1006,14 @@ static ssize_t erst_reader(u64 *id, enum pstore_type_id *type,
 	}
 
 	len = erst_read(record_id, &rcd->hdr, sizeof(*rcd) +
-			  erst_erange.size);
+			erst_info.bufsize);
+	/* The record may be cleared by others, try read next record */
+	if (len == -ENOENT)
+		goto skip;
+	else if (len < 0) {
+		rc = -1;
+		goto out;
+	}
 	if (uuid_le_cmp(rcd->hdr.creator_id, CPER_CREATOR_PSTORE) != 0)
 		goto skip;