Re: [PATCH 2/2] tracing: kprobe: Fix potential null-ptr-deref on trace_array in kprobe_event_gen_test_exit()

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On Mon, 7 Nov 2022 21:47:10 +0800
shangxiaojing <shangxiaojing@xxxxxxxxxx> wrote:

> Hi,
> 
> On 2022/11/7 21:38, Masami Hiramatsu (Google) wrote:
> > Hi,
> > 
> > On Mon, 7 Nov 2022 15:16:17 +0800
> > Shang XiaoJing <shangxiaojing@xxxxxxxxxx> wrote:
> > 
> >> When test_gen_kprobe_cmd() failed after kprobe_event_gen_cmd_end(), it
> >> will goto delete, which will call kprobe_event_delete() and release the
> >> corresponding resource. However, the trace_array in gen_kretprobe_test
> >> will point to the invalid resource. Set gen_kretprobe_test->tr to NULL
> >> after called kprobe_event_delete() and add NULL check when releasing
> >> the module.
> >>
> >> BUG: kernel NULL pointer dereference, address: 0000000000000070
> >> PGD 0 P4D 0
> >> Oops: 0000 [#1] SMP PTI
> >> CPU: 0 PID: 246 Comm: modprobe Tainted: G        W
> >> 6.1.0-rc1-00174-g9522dc5c87da-dirty #248
> >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
> >> rel-1.15.0-0-g2dd4b9b3f840-prebuilt.qemu.org 04/01/2014
> >> RIP: 0010:__ftrace_set_clr_event_nolock+0x53/0x1b0
> >> Code: e8 82 26 fc ff 49 8b 1e c7 44 24 0c ea ff ff ff 49 39 de 0f 84 3c
> >> 01 00 00 c7 44 24 18 00 00 00 00 e8 61 26 fc ff 48 8b 6b 10 <44> 8b 65
> >> 70 4c 8b 6d 18 41 f7 c4 00 02 00 00 75 2f
> >> RSP: 0018:ffffc9000159fe00 EFLAGS: 00010293
> >> RAX: 0000000000000000 RBX: ffff88810971d268 RCX: 0000000000000000
> >> RDX: ffff8881080be600 RSI: ffffffff811b48ff RDI: ffff88810971d058
> >> RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000001
> >> R10: ffffc9000159fe58 R11: 0000000000000001 R12: ffffffffa0001064
> >> R13: ffffffffa000106c R14: ffff88810971d238 R15: 0000000000000000
> >> FS:  00007f89eeff6540(0000) GS:ffff88813b600000(0000)
> >> knlGS:0000000000000000
> >> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> CR2: 0000000000000070 CR3: 000000010599e004 CR4: 0000000000330ef0
> >> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> Call Trace:
> >>   <TASK>
> >>   __ftrace_set_clr_event+0x3e/0x60
> >>   trace_array_set_clr_event+0x35/0x50
> >>   ? 0xffffffffa0000000
> >>   kprobe_event_gen_test_exit+0xcd/0x10b [kprobe_event_gen_test]
> >>   __x64_sys_delete_module+0x206/0x380
> >>   ? lockdep_hardirqs_on_prepare+0xd8/0x190
> >>   ? syscall_enter_from_user_mode+0x1c/0x50
> >>   do_syscall_64+0x3f/0x90
> >>   entry_SYSCALL_64_after_hwframe+0x63/0xcd
> >> RIP: 0033:0x7f89eeb061b7
> >>
> >> Fixes: 64836248dda2 ("tracing: Add kprobe event command generation test module")
> >> Signed-off-by: Shang XiaoJing <shangxiaojing@xxxxxxxxxx>
> >> ---
> >>   kernel/trace/kprobe_event_gen_test.c | 29 +++++++++++++++++-----------
> >>   1 file changed, 18 insertions(+), 11 deletions(-)
> >>
> >> diff --git a/kernel/trace/kprobe_event_gen_test.c b/kernel/trace/kprobe_event_gen_test.c
> >> index 1c98fafcf333..277e21e4a63e 100644
> >> --- a/kernel/trace/kprobe_event_gen_test.c
> >> +++ b/kernel/trace/kprobe_event_gen_test.c
> >> @@ -145,6 +145,8 @@ static int __init test_gen_kprobe_cmd(void)
> >>    delete:
> >>   	/* We got an error after creating the event, delete it */
> >>   	ret = kprobe_event_delete("gen_kprobe_test");
> >> +	if (trace_event_file_is_valid(gen_kprobe_test))
> >> +		gen_kprobe_test->tr = NULL;
> > 
> > I think the correct fix should be
> > 
> > 	if (trace_event_file_is_valid(gen_kprobe_test)) {
> > 		trace_put_event_file(gen_kprobe_test);
> > 		gen_kprobe_test = NULL;
> > 	}
> >    	ret = kprobe_event_delete("gen_kprobe_test");
> > 
> > Since the gen_kprobe_event is owned by ftrace subsystem, the test
> > code should not change the tr field.
> > 
> When trace_array_set_clr_event() failed, it already called 
> trace_put_event_file(), maybe we only need set gen_kprobe_test to NULL.

Ah, OK. That should work.

Thank you,

> 
> >>   	goto out;
> >>   }
> >>   
> >> @@ -208,6 +210,8 @@ static int __init test_gen_kretprobe_cmd(void)
> >>    delete:
> >>   	/* We got an error after creating the event, delete it */
> >>   	ret = kprobe_event_delete("gen_kretprobe_test");
> >> +	if (trace_event_file_is_valid(gen_kretprobe_test))
> >> +		gen_kretprobe_test->tr = NULL;
> > 
> > Ditto. >
> > And then, below changes are not required.
> 
> Yes, will fix in v2, thanks for the review.
> 
> Thanks,
> -- 
> Shang XiaoJing


-- 
Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>