[PATCH v2] tracing: Limit access to parser->buffer when trace_get_user failed

[Pu Lehui <pulehui@huaweicloud.com>]

From: Pu Lehui <pulehui@huawei.com>

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.

Fixes: 8c9af478c06b ("ftrace: Handle commands when closing set_ftrace_filter file")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
---

v2:
- Add `fail` field to struct trace_parser to indicate parsing failed.

v1:
https://lore.kernel.org/all/20250805151203.1214790-1-pulehui@huaweicloud.com/

 kernel/trace/trace.c | 20 ++++++++++++++------
 kernel/trace/trace.h |  3 ++-
 2 files changed, 16 insertions(+), 7 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4283ed4e8f59..138212f4ecde 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1814,9 +1814,11 @@ int trace_get_user(struct trace_parser *parser, const char __user *ubuf,
 	if (!*ppos)
 		trace_parser_clear(parser);
 
+	parser->fail = false;
+
 	ret = get_user(ch, ubuf++);
 	if (ret)
-		return ret;
+		goto fail;
 
 	read++;
 	cnt--;
@@ -1830,7 +1832,7 @@ 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 +1850,14 @@ 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 +1872,15 @@ 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:
+	parser->fail = true;
+	return ret;
 }
 
 /* TODO add a seq_buf_to_buffer() */
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 1dbf1d3cf2f1..5072bb25a860 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -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)
-- 
2.34.1