afs: Fix missing XDR advance in xdr_decode_{AFS,YFS}FSFetchStatus()

If we receive a status record that has VNOVNODE set in the abort field,
xdr_decode_AFSFetchStatus() and xdr_decode_YFSFetchStatus() don't advance
the XDR pointer, thereby corrupting anything subsequent decodes from the
same block of data.

This has the potential to affect AFS.InlineBulkStatus and
YFS.InlineBulkStatus operation, but probably doesn't since the status
records are extracted as individual blocks of data and the buffer pointer
is reset between blocks.

It does affect YFS.RemoveFile2 operation, corrupting the volsync record -
though that is not currently used.

Other operations abort the entire operation rather than returning an error
inline, in which case there is no decoding to be done.

Fix this by unconditionally advancing the xdr pointer.

Fixes: 684b0f68 ("afs: Fix AFSFetchStatus decoder to provide OpenAFS compatibility")
Signed-off-by: David Howells <dhowells@redhat.com>

fs/afs/fsclient.c

@@ -65,6 +65,7 @@ static int xdr_decode_AFSFetchStatus(const __be32 **_bp,
 	bool inline_error = (call->operation_ID == afs_FS_InlineBulkStatus);
 	u64 data_version, size;
 	u32 type, abort_code;
+	int ret;
 
 	abort_code = ntohl(xdr->abort_code);
 
@@ -78,7 +79,7 @@ static int xdr_decode_AFSFetchStatus(const __be32 **_bp,
 			 */
 			status->abort_code = abort_code;
 			scb->have_error = true;
-			return 0;
+			goto good;
 		}
 
 		pr_warn("Unknown AFSFetchStatus version %u\n", ntohl(xdr->if_version));
@@ -87,7 +88,7 @@ static int xdr_decode_AFSFetchStatus(const __be32 **_bp,
 
 	if (abort_code != 0 && inline_error) {
 		status->abort_code = abort_code;
-		return 0;
+		goto good;
 	}
 
 	type = ntohl(xdr->type);
@@ -123,13 +124,16 @@ static int xdr_decode_AFSFetchStatus(const __be32 **_bp,
 	data_version |= (u64)ntohl(xdr->data_version_hi) << 32;
 	status->data_version = data_version;
 	scb->have_status = true;
-
+good:
+	ret = 0;
+advance:
 	*_bp = (const void *)*_bp + sizeof(*xdr);
-	return 0;
+	return ret;
 
 bad:
 	xdr_dump_bad(*_bp);
-	return afs_protocol_error(call, -EBADMSG, afs_eproto_bad_status);
+	ret = afs_protocol_error(call, -EBADMSG, afs_eproto_bad_status);
+	goto advance;
 }
 
 static time64_t xdr_decode_expiry(struct afs_call *call, u32 expiry)

fs/afs/yfsclient.c

@@ -186,13 +186,14 @@ static int xdr_decode_YFSFetchStatus(const __be32 **_bp,
 	const struct yfs_xdr_YFSFetchStatus *xdr = (const void *)*_bp;
 	struct afs_file_status *status = &scb->status;
 	u32 type;
+	int ret;
 
 	status->abort_code = ntohl(xdr->abort_code);
 	if (status->abort_code != 0) {
 		if (status->abort_code == VNOVNODE)
 			status->nlink = 0;
 		scb->have_error = true;
-		return 0;
+		goto good;
 	}
 
 	type = ntohl(xdr->type);
@@ -220,13 +221,16 @@ static int xdr_decode_YFSFetchStatus(const __be32 **_bp,
 	status->size		= xdr_to_u64(xdr->size);
 	status->data_version	= xdr_to_u64(xdr->data_version);
 	scb->have_status	= true;
-
+good:
+	ret = 0;
+advance:
 	*_bp += xdr_size(xdr);
-	return 0;
+	return ret;
 
 bad:
 	xdr_dump_bad(*_bp);
-	return afs_protocol_error(call, -EBADMSG, afs_eproto_bad_status);
+	ret = afs_protocol_error(call, -EBADMSG, afs_eproto_bad_status);
+	goto advance;
 }
 
 /*