[PATCH 6.1 002/473] ftrace: Fix possible use-after-free issue in ftrace_location()

Greg Kroah-Hartman
2024-06-06T14:12:11Z

From: Zheng Yejian <zhengyejian1@huawei.com>

commit e60b613df8b6253def41215402f72986fee3fc8d upstream.

KASAN reports a bug:

BUG: KASAN: use-after-free in ftrace_location+0x90/0x120
Read of size 8 at addr ffff888141d40010 by task insmod/424
CPU: 8 PID: 424 Comm: insmod Tainted: G W 6.9.0-rc2+
[...]
Call Trace:
<TASK>
dump_stack_lvl+0x68/0xa0
print_report+0xcf/0x610
kasan_report+0xb5/0xe0
ftrace_location+0x90/0x120
register_kprobe+0x14b/0xa40
kprobe_init+0x2d/0xff0 [kprobe_example]
do_one_initcall+0x8f/0x2d0
do_init_module+0x13a/0x3c0
load_module+0x3082/0x33d0
init_module_from_file+0xd2/0x130
__x64_sys_finit_module+0x306/0x440
do_syscall_64+0x68/0x140
entry_SYSCALL_64_after_hwframe+0x71/0x79

The root cause is that, in lookup_rec(), ftrace record of some address
is being searched in ftrace pages of some module, but those ftrace pages
at the same time is being freed in ftrace_release_mod() as the
corresponding module is being deleted:

CPU1 | CPU2
register_kprobes() { | delete_module() {
check_kprobe_address_safe() { |
arch_check_ftrace_location() { |
ftrace_location() { |
lookup_rec() // USE! | ftrace_release_mod() // Free!

To fix this issue:
1. Hold rcu lock as accessing ftrace pages in ftrace_location_range();
2. Use ftrace_location_range() instead of lookup_rec() in
ftrace_location();
3. Call synchronize_rcu() before freeing any ftrace pages both in
ftrace_process_locs()/ftrace_release_mod()/ftrace_free_mem().

Link: https://lore.kernel.org/linux-trace-kernel/20240509192859.1273558-1-zhengyejian1@huawei.com

Cc: stable@vger.kernel.org
Cc: <mhiramat@kernel.org>
Cc: <mark.rutland@arm.com>
Cc: <mathieu.desnoyers@efficios.com>
Fixes: ae6aa16fdc16 ("kprobes: introduce ftrace based optimization")
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Zheng Yejian <zhengyejian1@huawei.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/trace/ftrace.c | 39 +++++++++++++++++++++++----------------
1 file changed, 23 insertions(+), 16 deletions(-)

--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1565,12 +1565,15 @@ static struct dyn_ftrace *lookup_rec(uns
unsigned long ftrace_location_range(unsigned long start, unsigned long end)
{
struct dyn_ftrace *rec;
+ unsigned long ip = 0;

+ rcu_read_lock();
rec = lookup_rec(start, end);
if (rec)
- return rec->ip;
+ ip = rec->ip;
+ rcu_read_unlock();

- return 0;
+ return ip;
}

/**
@@ -1583,25 +1586,22 @@ unsigned long ftrace_location_range(unsi
*/
unsigned long ftrace_location(unsigned long ip)
{
- struct dyn_ftrace *rec;
+ unsigned long loc;
unsigned long offset;
unsigned long size;

- rec = lookup_rec(ip, ip);
- if (!rec) {
+ loc = ftrace_location_range(ip, ip);
+ if (!loc) {
if (!kallsyms_lookup_size_offset(ip, &size, &offset))
goto out;

/* map sym+0 to __fentry__ */
if (!offset)
- rec = lookup_rec(ip, ip + size - 1);
+ loc = ftrace_location_range(ip, ip + size - 1);
}

- if (rec)
- return rec->ip;
-
out:
- return 0;
+ return loc;
}

/**
@@ -6784,6 +6784,8 @@ static int ftrace_process_locs(struct mo
/* We should have used all pages unless we skipped some */
if (pg_unuse) {
WARN_ON(!skipped);
+ /* Need to synchronize with ftrace_location_range() */
+ synchronize_rcu();
ftrace_free_pages(pg_unuse);
}
return ret;
@@ -6998,6 +7000,9 @@ void ftrace_release_mod(struct module *m
out_unlock:
mutex_unlock(&ftrace_lock);

+ /* Need to synchronize with ftrace_location_range() */
+ if (tmp_page)
+ synchronize_rcu();
for (pg = tmp_page; pg; pg = tmp_page) {

/* Needs to be called outside of ftrace_lock */
@@ -7332,6 +7337,7 @@ void ftrace_free_mem(struct module *mod,
unsigned long start = (unsigned long)(start_ptr);
unsigned long end = (unsigned long)(end_ptr);
struct ftrace_page **last_pg = &ftrace_pages_start;
+ struct ftrace_page *tmp_page = NULL;
struct ftrace_page *pg;
struct dyn_ftrace *rec;
struct dyn_ftrace key;
@@ -7375,12 +7381,8 @@ void ftrace_free_mem(struct module *mod,
ftrace_update_tot_cnt--;
if (!pg->index) {
*last_pg = pg->next;
- if (pg->records) {
- free_pages((unsigned long)pg->records, pg->order);
- ftrace_number_of_pages -= 1 << pg->order;
- }
- ftrace_number_of_groups--;
- kfree(pg);
+ pg->next = tmp_page;
+ tmp_page = pg;
pg = container_of(last_pg, struct ftrace_page, next);
if (!(*last_pg))
ftrace_pages = pg;
@@ -7397,6 +7399,11 @@ void ftrace_free_mem(struct module *mod,
clear_func_from_hashes(func);
kfree(func);
}
+ /* Need to synchronize with ftrace_location_range() */
+ if (tmp_page) {
+ synchronize_rcu();
+ ftrace_free_pages(tmp_page);
+ }
}

void __init ftrace_free_init_mem(void)