fgraph: Do not enable function_graph tracer when setting funcgraph-args

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

fgraph: Do not enable function_graph tracer when setting funcgraph-args

When setting the funcgraph-args option when function graph tracer is net

enabled, it incorrectly enables it. Worse, it unregisters itself when it

was never registered. Then when it gets enabled again, it will register

itself a second time causing a WARNing.

~# echo 1 > /sys/kernel/tracing/options/funcgraph-args

~# head -20 /sys/kernel/tracing/trace

# tracer: nop

#

# entries-in-buffer/entries-written: 813/26317372 #P:8

#

# _-----=> irqs-off/BH-disabled

# / _----=> need-resched

# | / _---=> hardirq/softirq

# || / _--=> preempt-depth

# ||| / _-=> migrate-disable

# |||| / delay

# TASK-PID CPU# ||||| TIMESTAMP FUNCTION

# | | | ||||| | |

<idle>-0 [007] d..4. 358.966010: 7) 1.692 us | fetch_next_timer_interrupt(basej=4294981640, basem=357956000000, base_local=0xffff88823c3ae040, base_global=0xffff88823c3af300, tevt=0xffff888100e47cb8);

<idle>-0 [007] d..4. 358.966012: 7) | tmigr_cpu_deactivate(nextexp=357988000000) {

<idle>-0 [007] d..4. 358.966013: 7) | _raw_spin_lock(lock=0xffff88823c3b2320) {

<idle>-0 [007] d..4. 358.966014: 7) 0.981 us | preempt_count_add(val=1);

<idle>-0 [007] d..5. 358.966017: 7) 1.058 us | do_raw_spin_lock(lock=0xffff88823c3b2320);

<idle>-0 [007] d..4. 358.966019: 7) 5.824 us | }

<idle>-0 [007] d..5. 358.966021: 7) | tmigr_inactive_up(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {

<idle>-0 [007] d..5. 358.966022: 7) | tmigr_update_events(group=0xffff888100cb9000, child=0x0, data=0xffff888100e47bc0) {

Notice the "tracer: nop" at the top there. The current tracer is the "nop"

tracer, but the content is obviously the function graph tracer.

Enabling function graph tracing will cause it to register again and

trigger a warning in the accounting:

~# echo function_graph > /sys/kernel/tracing/current_tracer

-bash: echo: write error: Device or resource busy

With the dmesg of:

------------[ cut here ]------------

WARNING: CPU: 7 PID: 1095 at kernel/trace/ftrace.c:3509 ftrace_startup_subops+0xc1e/0x1000

Modules linked in: kvm_intel kvm irqbypass

CPU: 7 UID: 0 PID: 1095 Comm: bash Not tainted 6.16.0-rc2-test-00006-gea03de4105d3 #24 PREEMPT

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014

RIP: 0010:ftrace_startup_subops+0xc1e/0x1000

Code: 48 b8 22 01 00 00 00 00 ad de 49 89 84 24 88 01 00 00 8b 44 24 08 89 04 24 e9 c3 f7 ff ff c7 04 24 ed ff ff ff e9 b7 f7 ff ff <0f> 0b c7 04 24 f0 ff ff ff e9 a9 f7 ff ff c7 04 24 f4 ff ff ff e9

RSP: 0018:ffff888133cff948 EFLAGS: 00010202

RAX: 0000000000000001 RBX: 1ffff1102679ff31 RCX: 0000000000000000

RDX: 1ffffffff0b27a60 RSI: ffffffff8593d2f0 RDI: ffffffff85941140

RBP: 00000000000c2041 R08: ffffffffffffffff R09: ffffed1020240221

R10: ffff88810120110f R11: ffffed1020240214 R12: ffffffff8593d2f0

R13: ffffffff8593d300 R14: ffffffff85941140 R15: ffffffff85631100

FS: 00007f7ec6f28740(0000) GS:ffff8882b5251000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f7ec6f181c0 CR3: 000000012f1d0005 CR4: 0000000000172ef0

Call Trace:

<TASK>

? __pfx_ftrace_startup_subops+0x10/0x10

? find_held_lock+0x2b/0x80

? ftrace_stub_direct_tramp+0x10/0x10

? ftrace_stub_direct_tramp+0x10/0x10

? trace_preempt_on+0xd0/0x110

? __pfx_trace_graph_entry_args+0x10/

---truncated---