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

On Wed, Aug 3, 2022 at 9:16 AM Paul Moore <paul(a)paul-moore.com&gt; wrote: > On Wed, Aug 3, 2022 at 1:03 AM Peilin Ye <yepeilin.cs(a)gmail.com&gt; wrote: >> >> 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(a)vger.kernel.org >> Signed-off-by: Peilin Ye <peilin.ye(a)bytedance.com&gt; >> --- >> 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! > > Thanks for the report and patch! I'll take a closer look at this > today and get back to you. I think the best solution to this is simply to remove the calls to audit_alloc_kernel() in the io_uring and io-wq code, as well as the audit_alloc_kernel() function itself. As long as create_io_thread() ends up calling copy_process to create the new kernel thread the audit_context should be allocated correctly. Peilin Ye, are you able to draft a patch to do that and give it a test? For those that may be wondering how this happened (I definitely was!), it looks like when I first started working on the LSM/audit support for io_uring it was before the v5.12-rc1 release when create_io_thread() was introduced. Prior to create_io_thread() it appears that io_uring/io-wq wasn't calling into copy_process() and thus was not getting an audit_context allocated in the kernel thread's task_struct; the solution for those original development drafts was to add a call to a new audit_alloc_kernel() which would handle the audit_context allocation. Unfortunately, I didn't notice the move to create_io_thread() during development and the redundant audit_alloc_kernel() calls remained :/