[PATCH v0] can: raw: supplement the check to prevent the NPD

[Lin Ma <linma@xxxxxxxxxx>]

The CAN_RAW_FILTER command allows the user to pass optlen as value 0. It
is expected to clear out the filer

static int raw_setsockopt(...) {
  struct can_filter *filter = NULL;
  ...
  // count = 0 if optlen = 0
  count = optlen / sizeof(struct can_filter);
  ...
  ro->filter = filter;
  ro->count  = count;
  ...
}

However, if this sock is bound to a device, bad thing happens as the
current check is failed to prevent the NULL Pointer Dereference.

static int raw_setsockopt(...) {
  ...
  if (ro->bound) {
    /* (try to) register the new filters */
    if (count == 1)
      err = raw_enable_filters(sock_net(sk), dev, sk,
                               &sfilter, 1);
    else
      // count = 0 can enter here while filter = NULL
      // which is unexpected
      err = raw_enable_filters(sock_net(sk), dev, sk,
                               filter, count);
  ...
}

This patch supplements the comparison with additional check.

Fixes: commit c18ce101f2e4 ("[CAN]: Add raw protocol")
Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
---
 net/can/raw.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/raw.c b/net/can/raw.c
index 7105fa4824e4..590df2da081c 100644
--- a/net/can/raw.c
+++ b/net/can/raw.c
@@ -564,7 +564,7 @@ static int raw_setsockopt(struct socket *sock, int level, int optname,
 			if (count == 1)
 				err = raw_enable_filters(sock_net(sk), dev, sk,
 							 &sfilter, 1);
-			else
+			else if (count > 1)
 				err = raw_enable_filters(sock_net(sk), dev, sk,
 							 filter, count);
 			if (err) {
-- 
2.33.1