[PATCH] audit, io_uring, io-wq: Fix memory leak in io_sq_thread() and io_wqe_worker()

[Peilin Ye]

From: Peilin Ye <peilin.ye at bytedance.com>

Currently @audit_context is allocated twice for io_uring workers:

  1. copy_process() calls audit_alloc();
  2. io_sq_thread() or io_wqe_worker() calls audit_alloc_kernel() (which
     is effectively audit_alloc()) and overwrites @audit_context,
     causing:

  BUG: memory leak
  unreferenced object 0xffff888144547400 (size 1024):
<...>
    hex dump (first 32 bytes):
      00 00 00 00 00 00 00 00 01 00 00 00 00 00 00 00  ................
      00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
    backtrace:
      [<ffffffff8135cfc3>] audit_alloc+0x133/0x210
      [<ffffffff81239e63>] copy_process+0xcd3/0x2340
      [<ffffffff8123b5f3>] create_io_thread+0x63/0x90
      [<ffffffff81686604>] create_io_worker+0xb4/0x230
      [<ffffffff81686f68>] io_wqe_enqueue+0x248/0x3b0
      [<ffffffff8167663a>] io_queue_iowq+0xba/0x200
      [<ffffffff816768b3>] io_queue_async+0x113/0x180
      [<ffffffff816840df>] io_req_task_submit+0x18f/0x1a0
      [<ffffffff816841cd>] io_apoll_task_func+0xdd/0x120
      [<ffffffff8167d49f>] tctx_task_work+0x11f/0x570
      [<ffffffff81272c4e>] task_work_run+0x7e/0xc0
      [<ffffffff8125a688>] get_signal+0xc18/0xf10
      [<ffffffff8111645b>] arch_do_signal_or_restart+0x2b/0x730
      [<ffffffff812ea44e>] exit_to_user_mode_prepare+0x5e/0x180
      [<ffffffff844ae1b2>] syscall_exit_to_user_mode+0x12/0x20
      [<ffffffff844a7e80>] do_syscall_64+0x40/0x80

Then,

  3. io_sq_thread() or io_wqe_worker() frees @audit_context using
     audit_free();
  4. do_exit() eventually calls audit_free() again, which is okay
     because audit_free() does a NULL check.

Free the old @audit_context first in audit_alloc_kernel(), and delete
the redundant calls to audit_free() for less confusion.

Fixes: 5bd2182d58e9 ("audit,io_uring,io-wq: add some basic audit support to io_uring")
Cc: stable at vger.kernel.org
Signed-off-by: Peilin Ye <peilin.ye at bytedance.com>
---
Hi all,

A better way to fix this memleak would probably be checking
@args->io_thread in copy_process()?  Something like:

    if (args->io_thread)
	retval = audit_alloc_kernel();
    else
	retval = audit_alloc();

But I didn't want to add another if to copy_process() for this bugfix.
Please suggest, thanks!

Peilin Ye

 fs/io-wq.c       | 1 -
 fs/io_uring.c    | 2 --
 kernel/auditsc.c | 1 +
 3 files changed, 1 insertion(+), 3 deletions(-)

diff --git a/fs/io-wq.c b/fs/io-wq.c
index 824623bcf1a5..0f4804a5e873 100644
--- a/fs/io-wq.c
+++ b/fs/io-wq.c
@@ -670,7 +670,6 @@ static int io_wqe_worker(void *data)
 	if (test_bit(IO_WQ_BIT_EXIT, &wq->state))
 		io_worker_handle_work(worker);
 
-	audit_free(current);
 	io_worker_exit(worker);
 	return 0;
 }
diff --git a/fs/io_uring.c b/fs/io_uring.c
index e8e769be9ed0..0f27914f37f2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -9283,8 +9283,6 @@ static int io_sq_thread(void *data)
 	io_run_task_work();
 	mutex_unlock(&sqd->lock);
 
-	audit_free(current);
-
 	complete(&sqd->exited);
 	do_exit(0);
 }
diff --git a/kernel/auditsc.c b/kernel/auditsc.c
index 3a8c9d744800..7948090fd12f 100644
--- a/kernel/auditsc.c
+++ b/kernel/auditsc.c
@@ -1095,6 +1095,7 @@ int audit_alloc_kernel(struct task_struct *tsk)
 	 * 2. The {set,clear}_task_syscall_work() ops likely have zero effect
 	 * on these internal kernel tasks, but they probably don't hurt either.
 	 */
+	__audit_free(current);
 	return audit_alloc(tsk);
 }
 
-- 
2.20.1