net/mlx5: fw_tracer, return NULL on create error

In the Linux kernel, the following vulnerability has been resolved: net/mlx5: fw_tracer, return NULL on create error Tracer creation can fail by returning either NULL or ERR_PTR. The return value is stored without a check on the device, and users treat ERR_PTR and NULL the same way. This also causes a crash in the core dump logic, which is missing the ERR_PTR check and ends up dereferencing it, as shown in the trace below. Switch tracer creation to return NULL on failure only, so callers only need a single NULL check. Internal error: Oops: 0000000096000006 [#1] SMP Modules linked in: mlx5_ib ib_uverbs ib_core ipv6 mlx5_core CPU: 1 UID: 0 PID: 12 Comm: kworker/u16:0 Not tainted 6.19.7 #1 PREEMPT(none) Workqueue: mlx5_health0001:01:00.0 mlx5_fw_reporter_err_work [mlx5_core] pstate: a3400009 (NzCv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--) pc : mlx5_fw_tracer_trigger_core_dump_general+0x58/0xe0 [mlx5_core] lr : mlx5_fw_tracer_trigger_core_dump_general+0x40/0xe0 [mlx5_core] sp : ffff800081cf3c40 x29: ffff800081cf3c90 x28: 0000000000000000 x27: 0000000000000000 x26: ffff000080018828 x25: 0000000000000000 x24: ffff000080304a05 x23: ffff800081cf3d80 x22: ffff0000847e01a0 x21: 0000000000000000 x20: ffff0000847e01a0 x19: ffffffffffffffa1 x18: ffff80008310bbf0 x17: ffff800080119650 x16: ffff80008010df54 x15: ffff80008010d4ac x14: ffff800079c202e4 x13: ffff80008002fe60 x12: ffff800080119650 x11: ffff80008010df54 x10: ffff80008010d4ac x9 : ffff800079c203d8 x8 : ffff800081cf3c88 x7 : 0000000000000000 x6 : 0000000000000000 x5 : 0000000000000000 x4 : 0000000000000008 x3 : 0000000000000030 x2 : 0000000000000008 x1 : 0000000000000000 x0 : 00000000c5c4000e Call trace: mlx5_fw_tracer_trigger_core_dump_general+0x58/0xe0 [mlx5_core] (P) mlx5_fw_reporter_dump+0x30/0x2e0 [mlx5_core] devlink_health_do_dump+0x9c/0x160 devlink_health_report+0x1c0/0x288 mlx5_fw_reporter_err_work+0xac/0xc0 [mlx5_core] process_one_work+0x15c/0x3d8 worker_thread+0x18c/0x320 kthread+0x148/0x228 ret_from_fork+0x10/0x20 Code: b9400000 5ac00800 7a401800 540003ca (3940a260) ---[ end trace 0000000000000000 ]--- Kernel panic - not syncing: Oops: Fatal exception SMP: stopping secondary CPUs Kernel Offset: disabled CPU features: 0x000000,00078031,75fce5a1,35fffe67 Memory Limit: none ---[ end Kernel panic - not syncing: Oops: Fatal exception ]---