Commit dd941507 authored by Masami Hiramatsu (Google)'s avatar Masami Hiramatsu (Google)
Browse files

tracing: fprobe events: Fix possible UAF on modules 

Commit ac91052f ("tracing: tprobe-events: Fix leakage of module
refcount") moved try_module_get() from __find_tracepoint_module_cb()
to find_tracepoint() caller, but that introduced a possible UAF
because the module can be unloaded before try_module_get(). In this
case, the module object should be freed too. Thus, try_module_get()
does not only fail but may access to the freed object.

To avoid that, try_module_get() in __find_tracepoint_module_cb()
again.

Link: https://lore.kernel.org/all/174342990779.781946.9138388479067729366.stgit@devnote2/



Fixes: ac91052f ("tracing: tprobe-events: Fix leakage of module refcount")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarMasami Hiramatsu (Google) <mhiramat@kernel.org>
parent d24fa977

kernel/trace/trace_fprobe.c

+17 −9
Original line number Diff line number Diff line
@@ -919,10 +919,16 @@ static void __find_tracepoint_module_cb(struct tracepoint *tp, struct module *mo 
	struct __find_tracepoint_cb_data *data = priv;



	if (!data->tpoint && !strcmp(data->tp_name, tp->name)) {

		data->tpoint = tp;

		if (!data->mod)

		/* If module is not specified, try getting module refcount. */

		if (!data->mod && mod) {

			/* If failed to get refcount, ignore this tracepoint. */

			if (!try_module_get(mod))

				return;



			data->mod = mod;

		}

		data->tpoint = tp;

	}

}



static void __find_tracepoint_cb(struct tracepoint *tp, void *priv)
@@ -933,7 +939,11 @@ static void __find_tracepoint_cb(struct tracepoint *tp, void *priv) 
		data->tpoint = tp;

}



/* Find a tracepoint from kernel and module. */

/*

 * Find a tracepoint from kernel and module. If the tracepoint is on the module,

 * the module's refcount is incremented and returned as *@tp_mod. Thus, if it is

 * not NULL, caller must call module_put(*tp_mod) after used the tracepoint.

 */

static struct tracepoint *find_tracepoint(const char *tp_name,

					  struct module **tp_mod)

{
@@ -962,7 +972,10 @@ static void reenable_trace_fprobe(struct trace_fprobe *tf) 
	}

}



/* Find a tracepoint from specified module. */

/*

 * Find a tracepoint from specified module. In this case, this does not get the

 * module's refcount. The caller must ensure the module is not freed.

 */

static struct tracepoint *find_tracepoint_in_module(struct module *mod,

						    const char *tp_name)

{
@@ -1169,11 +1182,6 @@ static int trace_fprobe_create_internal(int argc, const char *argv[], 
	if (is_tracepoint) {

		ctx->flags |= TPARG_FL_TPOINT;

		tpoint = find_tracepoint(symbol, &tp_mod);

		/* lock module until register this tprobe. */

		if (tp_mod && !try_module_get(tp_mod)) {

			tpoint = NULL;

			tp_mod = NULL;

		}

		if (tpoint) {

			ctx->funcname = kallsyms_lookup(

				(unsigned long)tpoint->probestub,