Re: [PATCH 5.4] ftrace: Fix possible use-after-free issue in ftrace_location()

On Mon, 11 Nov 2024 14:44:45 +0000 Hagar Hemdan hagarhem@amazon.com wrote:

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 ftrace_location_range(), 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-zhengyej...

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 [Hagar: Modified to apply on v5.4.y] Signed-off-by: Hagar Hemdan hagarhem@amazon.com

---

only compile tested.

You should do more than that. At least run the ftrace selftests.

---

kernel/trace/ftrace.c | 30 +++++++++++++++++++++--------- 1 file changed, 21 insertions(+), 9 deletions(-)

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 412505d94865..60bf8a6d55ce 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -1552,7 +1552,9 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end) struct ftrace_page *pg; struct dyn_ftrace *rec; struct dyn_ftrace key;

• unsigned long ip = 0;

• rcu_read_lock(); key.ip = start; key.flags = end; /* overload flags, as it is unsigned long */

@@ -1565,10 +1567,13 @@ unsigned long ftrace_location_range(unsigned long start, unsigned long end) sizeof(struct dyn_ftrace), ftrace_cmp_recs); if (rec)

• 	return rec->ip;
  

• {
  

• 	ip = rec->ip;
  

• 	break;
  

• }
  

The above breaks Linux coding style. It should be:

if (rec) { ip = rec->ip; break; }

-- Steve

}

• return 0;

• rcu_read_unlock();
• return ip;

} /** @@ -5736,6 +5741,8 @@ static int ftrace_process_locs(struct module *mod, /* 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;

@@ -5889,6 +5896,9 @@ void ftrace_release_mod(struct module *mod) 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 */ @@ -6196,6 +6206,7 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr) 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;

@@ -6239,12 +6250,8 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr) 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;
  

@@ -6261,6 +6268,11 @@ void ftrace_free_mem(struct module *mod, void *start_ptr, void *end_ptr) 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)