[PATCH] tracing: Zero-initialize parser->buffer to avoid OOB access

[Pu Lehui]

From: Pu Lehui <pule...@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 #3 NONE
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
zero-initializing parser->buffer.

Fixes: 8c9af478c06b ("ftrace: Handle commands when closing set_ftrace_filter 
file")
Signed-off-by: Pu Lehui <pule...@huawei.com>
---
 kernel/trace/trace.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4283ed4e8f59..97e66cbd3617 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -1776,7 +1776,7 @@ int trace_parser_get_init(struct trace_parser *parser, 
int size)
 {
        memset(parser, 0, sizeof(*parser));
 
-       parser->buffer = kmalloc(size, GFP_KERNEL);
+       parser->buffer = kzalloc(size, GFP_KERNEL);
        if (!parser->buffer)
                return 1;
 
@@ -1860,13 +1860,10 @@ int trace_get_user(struct trace_parser *parser, const 
char __user *ubuf,
 
        /* We either got finished input or we have to wait for another call. */
        if (isspace(ch) || !ch) {
-               parser->buffer[parser->idx] = 0;
                parser->cont = false;
        } else if (parser->idx < parser->size - 1) {
                parser->cont = true;
                parser->buffer[parser->idx++] = ch;
-               /* Make sure the parsed string always terminates with '\0'. */
-               parser->buffer[parser->idx] = 0;
        } else {
                return -EINVAL;
        }
-- 
2.34.1