Re: [PATCH] tracing/eprobe: Fix memory leak of filter string

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Tue,  8 Nov 2022 20:57:38 -0300
Rafael Mendonca <rafaelmendsr@gmail.com> wrote:

> The filter string doesn't get freed when a dynamic event is deleted. If a
> filter is set, then memory is leaked:
> 
> root@localhost:/sys/kernel/tracing# echo 'e:egroup/stat_runtime_4core \
>         sched/sched_stat_runtime runtime=$runtime:u32 if cpu < 4' >> dynamic_events
> root@localhost:/sys/kernel/tracing# echo "-:egroup/stat_runtime_4core"  >> dynamic_events
> root@localhost:/sys/kernel/tracing# echo scan > /sys/kernel/debug/kmemleak
> [  224.416373] kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> root@localhost:/sys/kernel/tracing# cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff88810156f1b8 (size 8):
>   comm "bash", pid 224, jiffies 4294935612 (age 55.800s)
>   hex dump (first 8 bytes):
>     63 70 75 20 3c 20 34 00                          cpu < 4.
>   backtrace:
>     [<000000009f880725>] __kmem_cache_alloc_node+0x18e/0x720
>     [<0000000042492946>] __kmalloc+0x57/0x240
>     [<0000000034ea7995>] __trace_eprobe_create+0x1214/0x1d30
>     [<00000000d70ef730>] trace_probe_create+0xf6/0x110
>     [<00000000915c7b16>] eprobe_dyn_event_create+0x21/0x30
>     [<000000000d894386>] create_dyn_event+0xf3/0x1a0
>     [<00000000e9af57d5>] trace_parse_run_command+0x1a9/0x2e0
>     [<0000000080777f18>] dyn_event_write+0x39/0x50
>     [<0000000089f0ec73>] vfs_write+0x311/0xe50
>     [<000000003da1bdda>] ksys_write+0x158/0x2a0
>     [<00000000bb1e616e>] __x64_sys_write+0x7c/0xc0
>     [<00000000e8aef1f7>] do_syscall_64+0x60/0x90
>     [<00000000fe7fe8ba>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Additionally, in __trace_eprobe_create() function, if an error occurs after
> the call to trace_eprobe_parse_filter(), which allocates the filter string,
> then memory is also leaked. That can be reproduced by creating the same
> event probe twice:
> 
> root@localhost:/sys/kernel/tracing# echo 'e:egroup/stat_runtime_4core \
>         sched/sched_stat_runtime runtime=$runtime:u32 if cpu < 4' >> dynamic_events
> root@localhost:/sys/kernel/tracing# echo 'e:egroup/stat_runtime_4core \
>         sched/sched_stat_runtime runtime=$runtime:u32 if cpu < 4' >> dynamic_events
> -bash: echo: write error: File exists
> root@localhost:/sys/kernel/tracing# echo scan > /sys/kernel/debug/kmemleak
> [  207.871584] kmemleak: 1 new suspected memory leaks (see /sys/kernel/debug/kmemleak)
> root@localhost:/sys/kernel/tracing# cat /sys/kernel/debug/kmemleak
> unreferenced object 0xffff8881020d17a8 (size 8):
>   comm "bash", pid 223, jiffies 4294938308 (age 31.000s)
>   hex dump (first 8 bytes):
>     63 70 75 20 3c 20 34 00                          cpu < 4.
>   backtrace:
>     [<000000000e4f5f31>] __kmem_cache_alloc_node+0x18e/0x720
>     [<0000000024f0534b>] __kmalloc+0x57/0x240
>     [<000000002930a28e>] __trace_eprobe_create+0x1214/0x1d30
>     [<0000000028387903>] trace_probe_create+0xf6/0x110
>     [<00000000a80d6a9f>] eprobe_dyn_event_create+0x21/0x30
>     [<000000007168698c>] create_dyn_event+0xf3/0x1a0
>     [<00000000f036bf6a>] trace_parse_run_command+0x1a9/0x2e0
>     [<00000000014bde8b>] dyn_event_write+0x39/0x50
>     [<0000000078a097f7>] vfs_write+0x311/0xe50
>     [<00000000996cb208>] ksys_write+0x158/0x2a0
>     [<00000000a3c2acb0>] __x64_sys_write+0x7c/0xc0
>     [<0000000006b5d698>] do_syscall_64+0x60/0x90
>     [<00000000780e8ecf>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fix both issues by releasing the filter string in
> trace_event_probe_cleanup().
> 
> Fixes: 752be5c5c910 ("tracing/eprobe: Add eprobe filter support")
> Signed-off-by: Rafael Mendonca <rafaelmendsr@gmail.com>

Thanks for the fix!

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

> ---
>  kernel/trace/trace_eprobe.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index c2153bf59936..e888446d80fa 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -52,6 +52,7 @@ static void trace_event_probe_cleanup(struct trace_eprobe *ep)
>  	kfree(ep->event_system);
>  	if (ep->event)
>  		trace_event_put_ref(ep->event);
> +	kfree(ep->filter_str);
>  	kfree(ep);
>  }
>  
> -- 
> 2.34.1
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>