firewire: ohci: fix race when reading count in AR descriptor (693fa779) · Commits · 戴 / test

If the controller is storing a split packet and therefore changing d->res_count to zero between the two reads by the driver, we end up with an end pointer that is not at a packet boundary, and therefore overflow the buffer when handling the split packet. To fix this, read the field once, atomically. The compiler usually merges the two reads anyway, but for correctness, we have to enforce it. Signed-off-by:

Clemens Ladisch <clemens@ladisch.de> Tested-by:

Maxim Levitsky <maximlevitsky@gmail.com> Signed-off-by:

Stefan Richter <stefanr@s5r6.in-berlin.de>

drivers/firewire/ohci.c

+4 −2

Original line number	Original line	Diff line number	Diff line
	@@ -740,11 +740,13 @@ static void ar_context_tasklet(unsigned long data)
	struct ar_buffer *ab;		struct ar_buffer *ab;
	struct descriptor *d;		struct descriptor *d;
	void buffer, end;		void buffer, end;
			__le16 res_count;

	ab = ctx->current_buffer;		ab = ctx->current_buffer;
	d = &ab->descriptor;		d = &ab->descriptor;

	if (d->res_count == 0) {		res_count = ACCESS_ONCE(d->res_count);
			if (res_count == 0) {
	size_t size, size2, rest, pktsize, size3, offset;		size_t size, size2, rest, pktsize, size3, offset;
	dma_addr_t start_bus;		dma_addr_t start_bus;
	void *start;		void *start;
	@@ -812,7 +814,7 @@ static void ar_context_tasklet(unsigned long data)
	} else {		} else {
	buffer = ctx->pointer;		buffer = ctx->pointer;
	ctx->pointer = end =		ctx->pointer = end =
	(void *) ab + PAGE_SIZE - le16_to_cpu(d->res_count);		(void *) ab + PAGE_SIZE - le16_to_cpu(res_count);

	while (buffer < end)		while (buffer < end)
	buffer = handle_ar_packet(ctx, buffer);		buffer = handle_ar_packet(ctx, buffer);

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