Re: [PATCH v2] tracing/probes: Fix MAX_TRACE_ARGS limit handling

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

On Mon, 30 Sep 2024 16:26:54 -0400
Mikel Rychliski <mikel@mikelr.com> wrote:

> When creating a trace_probe we would set nr_args prior to truncating the
> arguments to MAX_TRACE_ARGS. However, we would only initialize arguments
> up to the limit.
> 
> This caused invalid memory access when attempting to set up probes with
> more than 128 fetchargs.
> 
>   BUG: kernel NULL pointer dereference, address: 0000000000000020
>   #PF: supervisor read access in kernel mode
>   #PF: error_code(0x0000) - not-present page
>   PGD 0 P4D 0
>   Oops: Oops: 0000 [#1] PREEMPT SMP PTI
>   CPU: 0 UID: 0 PID: 1769 Comm: cat Not tainted 6.11.0-rc7+ #8
>   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-1.fc39 04/01/2014
>   RIP: 0010:__set_print_fmt+0x134/0x330
> 
> Resolve the issue by applying the MAX_TRACE_ARGS limit earlier. Return
> an error when there are too many arguments instead of silently
> truncating.

Yeah, looks good to me. Let me pick it.

Thanks!

> 
> Fixes: 035ba76014c0 ("tracing/probes: cleanup: Set trace_probe::nr_args at trace_probe_init")
> Signed-off-by: Mikel Rychliski <mikel@mikelr.com>
> ---
> V1 -> V2: Return error instead of dropping excessive arguments
> 
>  kernel/trace/trace_eprobe.c | 7 ++++++-
>  kernel/trace/trace_fprobe.c | 6 +++++-
>  kernel/trace/trace_kprobe.c | 6 +++++-
>  kernel/trace/trace_uprobe.c | 4 +++-
>  4 files changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_eprobe.c b/kernel/trace/trace_eprobe.c
> index b0e0ec85912e..ebda68ee9abf 100644
> --- a/kernel/trace/trace_eprobe.c
> +++ b/kernel/trace/trace_eprobe.c
> @@ -912,6 +912,11 @@ static int __trace_eprobe_create(int argc, const char *argv[])
>  		}
>  	}
>  
> +	if (argc - 2 > MAX_TRACE_ARGS) {
> +		ret = -E2BIG;
> +		goto error;
> +	}
> +
>  	mutex_lock(&event_mutex);
>  	event_call = find_and_get_event(sys_name, sys_event);
>  	ep = alloc_event_probe(group, event, event_call, argc - 2);
> @@ -937,7 +942,7 @@ static int __trace_eprobe_create(int argc, const char *argv[])
>  
>  	argc -= 2; argv += 2;
>  	/* parse arguments */
> -	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> +	for (i = 0; i < argc; i++) {
>  		trace_probe_log_set_index(i + 2);
>  		ret = trace_eprobe_tp_update_arg(ep, argv, i);
>  		if (ret)
> diff --git a/kernel/trace/trace_fprobe.c b/kernel/trace/trace_fprobe.c
> index a079abd8955b..c62d1629cffe 100644
> --- a/kernel/trace/trace_fprobe.c
> +++ b/kernel/trace/trace_fprobe.c
> @@ -1187,6 +1187,10 @@ static int __trace_fprobe_create(int argc, const char *argv[])
>  		argc = new_argc;
>  		argv = new_argv;
>  	}
> +	if (argc > MAX_TRACE_ARGS) {
> +		ret = -E2BIG;
> +		goto out;
> +	}
>  
>  	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
>  	if (ret)
> @@ -1203,7 +1207,7 @@ static int __trace_fprobe_create(int argc, const char *argv[])
>  	}
>  
>  	/* parse arguments */
> -	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> +	for (i = 0; i < argc; i++) {
>  		trace_probe_log_set_index(i + 2);
>  		ctx.offset = 0;
>  		ret = traceprobe_parse_probe_arg(&tf->tp, i, argv[i], &ctx);
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 61a6da808203..263fac44d3ca 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -1013,6 +1013,10 @@ static int __trace_kprobe_create(int argc, const char *argv[])
>  		argc = new_argc;
>  		argv = new_argv;
>  	}
> +	if (argc > MAX_TRACE_ARGS) {
> +		ret = -E2BIG;
> +		goto out;
> +	}
>  
>  	ret = traceprobe_expand_dentry_args(argc, argv, &dbuf);
>  	if (ret)
> @@ -1029,7 +1033,7 @@ static int __trace_kprobe_create(int argc, const char *argv[])
>  	}
>  
>  	/* parse arguments */
> -	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> +	for (i = 0; i < argc; i++) {
>  		trace_probe_log_set_index(i + 2);
>  		ctx.offset = 0;
>  		ret = traceprobe_parse_probe_arg(&tk->tp, i, argv[i], &ctx);
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index c3df411a2684..f0273b4d4a7b 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -565,6 +565,8 @@ static int __trace_uprobe_create(int argc, const char **argv)
>  
>  	if (argc < 2)
>  		return -ECANCELED;
> +	if (argc - 2 > MAX_TRACE_ARGS)
> +		return -E2BIG;
>  
>  	if (argv[0][1] == ':')
>  		event = &argv[0][2];
> @@ -690,7 +692,7 @@ static int __trace_uprobe_create(int argc, const char **argv)
>  	tu->filename = filename;
>  
>  	/* parse arguments */
> -	for (i = 0; i < argc && i < MAX_TRACE_ARGS; i++) {
> +	for (i = 0; i < argc; i++) {
>  		struct traceprobe_parse_context ctx = {
>  			.flags = (is_return ? TPARG_FL_RETURN : 0) | TPARG_FL_USER,
>  		};
> 
> base-commit: 886f3732878dc92fb0ad6d8b6740b66410d1d50a
> -- 
> 2.46.1
> 


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