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: 8c9af478c06b ("ftrace: Handle commands when closing set_ftrace_filter file")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4283ed4e8f592f5b3fe3213a0f831643a464f9f7..8d8935ed416d7d11911b761641a49462b07d6c44 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -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() */

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 1dbf1d3cf2f1d437c372b65ac359073aec0c738b..be6654899cae6bb0fd334e931fabce8b7abdb83f 100644 (file)
--- 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)
@@ -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,