[PATCH AUTOSEL 4.19 3/4] firewire: nosy: ensure user_length is taken into account when fetching packet contents

[Sasha Levin <sashal@kernel.org>]

From: Thanassis Avgerinos <thanassis.avgerinos@gmail.com>

[ Upstream commit 38762a0763c10c24a4915feee722d7aa6e73eb98 ]

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@gmail.com>
Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/firewire/nosy.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/firewire/nosy.c b/drivers/firewire/nosy.c
index ac85e03e88e16..f3784c054dd6e 100644
--- a/drivers/firewire/nosy.c
+++ b/drivers/firewire/nosy.c
@@ -161,10 +161,12 @@ packet_buffer_get(struct client *client, char __user *data, size_t user_length)
 	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))
-- 
2.43.0