Bug 2334791 (CVE-2024-56717)

In the Linux kernel, the following vulnerability has been resolved:

net: mscc: ocelot: fix incorrect IFH SRC_PORT field in ocelot_ifh_set_basic()

Packets injected by the CPU should have a SRC_PORT field equal to the
CPU port module index in the Analyzer block (ocelot->num_phys_ports).

The blamed commit copied the ocelot_ifh_set_basic() call incorrectly
from ocelot_xmit_common() in net/dsa/tag_ocelot.c. Instead of calling
with "x", it calls with BIT_ULL(x), but the field is not a port mask,
but rather a single port index.

[ side note: this is the technical debt of code duplication :( ]

The error used to be silent and doesn't appear to have other
user-visible manifestations, but with new changes in the packing
library, it now fails loudly as follows:

------------[ cut here ]------------
Cannot store 0x40 inside bits 46-43 - will truncate
sja1105 spi2.0: xmit timed out
WARNING: CPU: 1 PID: 102 at lib/packing.c:98 __pack+0x90/0x198
sja1105 spi2.0: timed out polling for tstamp
CPU: 1 UID: 0 PID: 102 Comm: felix_xmit
Tainted: G        W        N 6.13.0-rc1-00372-gf706b85d972d-dirty #2605
Call trace:
 __pack+0x90/0x198 (P)
 __pack+0x90/0x198 (L)
 packing+0x78/0x98
 ocelot_ifh_set_basic+0x260/0x368
 ocelot_port_inject_frame+0xa8/0x250
 felix_port_deferred_xmit+0x14c/0x258
 kthread_worker_fn+0x134/0x350
 kthread+0x114/0x138

The code path pertains to the ocelot switchdev driver and to the felix
secondary DSA tag protocol, ocelot-8021q. Here seen with ocelot-8021q.

The messenger (packing) is not really to blame, so fix the original
commit instead.