net: ti: icssg-prueth: Fix possible NULL pointer dereference inside emac_xmit_xdp_frame()

net: ti: icssg-prueth: Fix possible NULL pointer dereference inside emac_xmit_xdp_frame()

There is an error check inside emac_xmit_xdp_frame() function which
is called when the driver wants to transmit XDP frame, to check if
the allocated tx descriptor is NULL, if true to exit and return
ICSSG_XDP_CONSUMED implying failure in transmission.

In this case trying to free a descriptor which is NULL will result
in kernel crash due to NULL pointer dereference. Fix this error handling
and increase netdev tx_dropped stats in the caller of this function
if the function returns ICSSG_XDP_CONSUMED.

Fixes: 62aa3246f462 ("net: ti: icssg-prueth: Add XDP support")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/all/70d8dd76-0c76-42fc-8611-9884937c82f5@stanley.mountain/
Signed-off-by: Meghana Malladi <m-malladi@ti.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20250415090543.717991-3-m-malladi@ti.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>