[PATCH 6.1 185/236] firewire: nosy: ensure user_length is taken into account when fetching packet contents

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6.1-stable review patch.  If anyone has any objections, please let me know.


From: Thanassis Avgerinos <thanassis.avgerinos@xxxxxxxxx>

commit 38762a0763c10c24a4915feee722d7aa6e73eb98 upstream.

Ensure that packet_buffer_get respects the user_length provided. If
the length of the head packet exceeds the user_length, packet_buffer_get
will now return 0 to signify to the user that no data were read
and a larger buffer size is required. Helps prevent user space overflows.

Signed-off-by: Thanassis Avgerinos <thanassis.avgerinos@xxxxxxxxx>
Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
 drivers/firewire/nosy.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/firewire/nosy.c
+++ b/drivers/firewire/nosy.c
@@ -148,10 +148,12 @@ packet_buffer_get(struct client *client,
 	if (atomic_read(&buffer->size) == 0)
 		return -ENODEV;
-	/* FIXME: Check length <= user_length. */
+	length = buffer->head->length;
+	if (length > user_length)
+		return 0;
 	end = buffer->data + buffer->capacity;
-	length = buffer->head->length;
 	if (&buffer->head->data[length] < end) {
 		if (copy_to_user(data, buffer->head->data, length))

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