CVE-2024-53121: net/mlx5: fs, lock FTE when checking if active
In the Linux kernel, the following vulnerability has been resolved:

net/mlx5: fs, lock FTE when checking if active

The referenced commits introduced a two-step process for deleting FTEs:

- Lock the FTE, delete it from hardware, set the hardware deletion function
  to NULL and unlock the FTE.
- Lock the parent flow group, delete the software copy of the FTE, and
  remove it from the xarray.

However, this approach encounters a race condition if a rule with the same
match value is added simultaneously. In this scenario, fs_core may set the
hardware deletion function to NULL prematurely, causing a panic during
subsequent rule deletions.

To prevent this, ensure the active flag of the FTE is checked under a lock,
which will prevent the fs_core layer from attaching a new steering rule to
an FTE that is in the process of deletion.

[  438.967589] MOSHE: 2496 mlx5_del_flow_rules del_hw_func
[  438.968205] ------------[ cut here ]------------
[  438.968654] refcount_t: decrement hit 0; leaking memory.
[  438.969249] WARNING: CPU: 0 PID: 8957 at lib/refcount.c:31 refcount_warn_saturate+0xfb/0x110
[  438.970054] Modules linked in: act_mirred cls_flower act_gact sch_ingress openvswitch nsh mlx5_vdpa vringh vhost_iotlb vdpa mlx5_ib mlx5_core xt_conntrack xt_MASQUERADE nf_conntrack_netlink nfnetlink xt_addrtype iptable_nat nf_nat br_netfilter rpcsec_gss_krb5 auth_rpcgss oid_registry overlay rpcrdma rdma_ucm ib_iser libiscsi scsi_transport_iscsi ib_umad rdma_cm ib_ipoib iw_cm ib_cm ib_uverbs ib_core zram zsmalloc fuse [last unloaded: cls_flower]
[  438.973288] CPU: 0 UID: 0 PID: 8957 Comm: tc Not tainted 6.12.0-rc1+ #8
[  438.973888] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
[  438.974874] RIP: 0010:refcount_warn_saturate+0xfb/0x110
[  438.975363] Code: 40 66 3b 82 c6 05 16 e9 4d 01 01 e8 1f 7c a0 ff 0f 0b c3 cc cc cc cc 48 c7 c7 10 66 3b 82 c6 05 fd e8 4d 01 01 e8 05 7c a0 ff <0f> 0b c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 90
[  438.976947] RSP: 0018:ffff888124a53610 EFLAGS: 00010286
[  438.977446] RAX: 0000000000000000 RBX: ffff888119d56de0 RCX: 0000000000000000
[  438.978090] RDX: ffff88852c828700 RSI: ffff88852c81b3c0 RDI: ffff88852c81b3c0
[  438.978721] RBP: ffff888120fa0e88 R08: 0000000000000000 R09: ffff888124a534b0
[  438.979353] R10: 0000000000000001 R11: 0000000000000001 R12: ffff888119d56de0
[  438.979979] R13: ffff888120fa0ec0 R14: ffff888120fa0ee8 R15: ffff888119d56de0
[  438.980607] FS:  00007fe6dcc0f800(0000) GS:ffff88852c800000(0000) knlGS:0000000000000000
[  438.983984] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[  438.984544] CR2: 00000000004275e0 CR3: 0000000186982001 CR4: 0000000000372eb0
[  438.985205] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[  438.985842] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[  438.986507] Call Trace:
[  438.986799]  <TASK>
[  438.987070]  ? __warn+0x7d/0x110
[  438.987426]  ? refcount_warn_saturate+0xfb/0x110
[  438.987877]  ? report_bug+0x17d/0x190
[  438.988261]  ? prb_read_valid+0x17/0x20
[  438.988659]  ? handle_bug+0x53/0x90
[  438.989054]  ? exc_invalid_op+0x14/0x70
[  438.989458]  ? asm_exc_invalid_op+0x16/0x20
[  438.989883]  ? refcount_warn_saturate+0xfb/0x110
[  438.990348]  mlx5_del_flow_rules+0x2f7/0x340 [mlx5_core]
[  438.990932]  __mlx5_eswitch_del_rule+0x49/0x170 [mlx5_core]
[  438.991519]  ? mlx5_lag_is_sriov+0x3c/0x50 [mlx5_core]
[  438.992054]  ? xas_load+0x9/0xb0
[  438.992407]  mlx5e_tc_rule_unoffload+0x45/0xe0 [mlx5_core]
[  438.993037]  mlx5e_tc_del_fdb_flow+0x2a6/0x2e0 [mlx5_core]
[  438.993623]  mlx5e_flow_put+0x29/0x60 [mlx5_core]
[  438.994161]  mlx5e_delete_flower+0x261/0x390 [mlx5_core]
[  438.994728]  tc_setup_cb_destroy+0xb9/0x190
[  438.995150]  fl_hw_destroy_filter+0x94/0xc0 [cls_flower]
[  438.995650]  fl_change+0x11a4/0x13c0 [cls_flower]
[  438.996105]  tc_new_tfilter+0x347/0xbc0
[  438.996503]  ? __
---truncated---
CVSS v3.1: 5.5