Commit 6a909ea8 authored by Pu Lehui's avatar Pu Lehui Committed by Steven Rostedt (Google)
Browse files

tracing: Limit access to parser->buffer when trace_get_user failed 

When the length of the string written to set_ftrace_filter exceeds
FTRACE_BUFF_MAX, the following KASAN alarm will be triggered:

BUG: KASAN: slab-out-of-bounds in strsep+0x18c/0x1b0
Read of size 1 at addr ffff0000d00bd5ba by task ash/165

CPU: 1 UID: 0 PID: 165 Comm: ash Not tainted 6.16.0-g6bcdbd62bd56-dirty
Hardware name: linux,dummy-virt (DT)
Call trace:
 show_stack+0x34/0x50 (C)
 dump_stack_lvl+0xa0/0x158
 print_address_description.constprop.0+0x88/0x398
 print_report+0xb0/0x280
 kasan_report+0xa4/0xf0
 __asan_report_load1_noabort+0x20/0x30
 strsep+0x18c/0x1b0
 ftrace_process_regex.isra.0+0x100/0x2d8
 ftrace_regex_release+0x484/0x618
 __fput+0x364/0xa58
 ____fput+0x28/0x40
 task_work_run+0x154/0x278
 do_notify_resume+0x1f0/0x220
 el0_svc+0xec/0xf0
 el0t_64_sync_handler+0xa0/0xe8
 el0t_64_sync+0x1ac/0x1b0

The reason is that trace_get_user will fail when processing a string
longer than FTRACE_BUFF_MAX, but not set the end of parser->buffer to 0.
Then an OOB access will be triggered in ftrace_regex_release->
ftrace_process_regex->strsep->strpbrk. We can solve this problem by
limiting access to parser->buffer when trace_get_user failed.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/20250813040232.1344527-1-pulehui@huaweicloud.com


Fixes: 8c9af478 ("ftrace: Handle commands when closing set_ftrace_filter file")
Signed-off-by: default avatarPu Lehui <pulehui@huawei.com>
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent 7b128f1d

kernel/trace/trace.c

+12 −6
Original line number Diff line number Diff line
@@ -1816,7 +1816,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 


	ret = get_user(ch, ubuf++);

	if (ret)

		return ret;

		goto fail;



	read++;

	cnt--;
@@ -1830,7 +1830,7 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
		while (cnt && isspace(ch)) {

			ret = get_user(ch, ubuf++);

			if (ret)

				return ret;

				goto fail;

			read++;

			cnt--;

		}
@@ -1848,12 +1848,14 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
	while (cnt && !isspace(ch) && ch) {

		if (parser->idx < parser->size - 1)

			parser->buffer[parser->idx++] = ch;

		else

			return -EINVAL;

		else {

			ret = -EINVAL;

			goto fail;

		}



		ret = get_user(ch, ubuf++);

		if (ret)

			return ret;

			goto fail;

		read++;

		cnt--;

	}
@@ -1868,11 +1870,15 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf, 
		/* Make sure the parsed string always terminates with '\0'. */

		parser->buffer[parser->idx] = 0;

	} else {

		return -EINVAL;

		ret = -EINVAL;

		goto fail;

	}



	*ppos += read;

	return read;

fail:

	trace_parser_fail(parser);

	return ret;

}



/* TODO add a seq_buf_to_buffer() */

kernel/trace/trace.h

+7 −1
Original line number Diff line number Diff line
@@ -1292,6 +1292,7 @@ bool ftrace_event_is_function(struct trace_event_call *call); 
 */

struct trace_parser {

	bool		cont;

	bool		fail;

	char		*buffer;

	unsigned	idx;

	unsigned	size;
@@ -1299,7 +1300,7 @@ struct trace_parser { 


static inline bool trace_parser_loaded(struct trace_parser *parser)

{

	return (parser->idx != 0);

	return !parser->fail && parser->idx != 0;

}



static inline bool trace_parser_cont(struct trace_parser *parser)
@@ -1313,6 +1314,11 @@ static inline void trace_parser_clear(struct trace_parser *parser) 
	parser->idx = 0;

}



static inline void trace_parser_fail(struct trace_parser *parser)

{

	parser->fail = true;

}



extern int trace_parser_get_init(struct trace_parser *parser, int size);

extern void trace_parser_put(struct trace_parser *parser);

extern int trace_get_user(struct trace_parser *parser, const char __user *ubuf,