mlxsw: spectrum_acl_tcam: Fix memory leak during rehash

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

mlxsw: spectrum_acl_tcam: Fix memory leak during rehash

The rehash delayed work migrates filters from one region to another.

This is done by iterating over all chunks (all the filters with the same

priority) in the region and in each chunk iterating over all the

filters.

If the migration fails, the code tries to migrate the filters back to

the old region. However, the rollback itself can also fail in which case

another migration will be erroneously performed. Besides the fact that

this ping pong is not a very good idea, it also creates a problem.

Each virtual chunk references two chunks: The currently used one

('vchunk->chunk') and a backup ('vchunk->chunk2'). During migration the

first holds the chunk we want to migrate filters to and the second holds

the chunk we are migrating filters from.

The code currently assumes - but does not verify - that the backup chunk

does not exist (NULL) if the currently used chunk does not reference the

target region. This assumption breaks when we are trying to rollback a

rollback, resulting in the backup chunk being overwritten and leaked

[1].

Fix by not rolling back a failed rollback and add a warning to avoid

future cases.

[1]

WARNING: CPU: 5 PID: 1063 at lib/parman.c:291 parman_destroy+0x17/0x20

Modules linked in:

CPU: 5 PID: 1063 Comm: kworker/5:11 Tainted: G W 6.9.0-rc2-custom-00784-gc6a05c468a0b #14

Hardware name: Mellanox Technologies Ltd. MSN3700/VMOD0005, BIOS 5.11 01/06/2019

Workqueue: mlxsw_core mlxsw_sp_acl_tcam_vregion_rehash_work

RIP: 0010:parman_destroy+0x17/0x20

[...]

Call Trace:

<TASK>

mlxsw_sp_acl_atcam_region_fini+0x19/0x60

mlxsw_sp_acl_tcam_region_destroy+0x49/0xf0

mlxsw_sp_acl_tcam_vregion_rehash_work+0x1f1/0x470

process_one_work+0x151/0x370

worker_thread+0x2cb/0x3e0

kthread+0xd0/0x100

ret_from_fork+0x34/0x50

ret_from_fork_asm+0x1a/0x30

</TASK>