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Message-ID: <VI1P193MB0752F2E6DA346CDB2BCDBED899D6A@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM> Date: Tue, 17 Oct 2023 19:49:15 +0800 From: Juntong Deng <juntong.deng@...look.com> To: Paolo Abeni <pabeni@...hat.com>, borisp@...dia.com, john.fastabend@...il.com, kuba@...nel.org, davem@...emloft.net, edumazet@...gle.com Cc: netdev@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org, linux-kernel@...r.kernel.org, syzbot+29c22ea2d6b2c5fd2eae@...kaller.appspotmail.com Subject: Re: [PATCH] net/tls: Fix slab-use-after-free in tls_encrypt_done On 2023/10/17 18:31, Paolo Abeni wrote: > On Thu, 2023-10-12 at 19:02 +0800, Juntong Deng wrote: >> In the current implementation, ctx->async_wait.completion is completed >> after spin_lock_bh, which causes tls_sw_release_resources_tx to >> continue executing and return to tls_sk_proto_cleanup, then return >> to tls_sk_proto_close, and after that enter tls_sw_free_ctx_tx to kfree >> the entire struct tls_context (including ctx->encrypt_compl_lock). >> >> Since ctx->encrypt_compl_lock has been freed, subsequent spin_unlock_bh >> will result in slab-use-after-free error. Due to SMP, even using >> spin_lock_bh does not prevent tls_sw_release_resources_tx from continuing >> on other CPUs. After tls_sw_release_resources_tx is woken up, there is no >> attempt to hold ctx->encrypt_compl_lock again, therefore everything >> described above is possible. >> >> The fix is to put complete(&ctx->async_wait.completion) after >> spin_unlock_bh, making the release after the unlock. Since complete is >> only executed if pending is 0, which means this is the last record, there >> is no need to worry about race condition causing duplicate completes. >> >> Reported-by: syzbot+29c22ea2d6b2c5fd2eae@...kaller.appspotmail.com >> Closes: https://syzkaller.appspot.com/bug?extid=29c22ea2d6b2c5fd2eae >> Signed-off-by: Juntong Deng <juntong.deng@...look.com> > > Have you tested this patch vs the syzbot reproducer? > > I think the following race is still present: > > CPU0 CPU1 > tls_sw_release_resources_tx tls_encrypt_done > spin_lock_bh > spin_unlock_bh > spin_lock_bh > spin_unlock_bh > complete > > wait > // ... > tls_sk_proto_close > > test_and_set_bit(BIT_TX_SCHEDULED, &ctx->tx_bitmask > // UaF > > regardless of 'complete()' being invoked before or after the > 'spin_unlock_bh()'. > > Paolo > Yes, I think you are right. My previous thought was that test_and_set_bit() is only called if 'ready' is true, but 'ready' will only be true on the first record, and complete() is only called when processing the last record. I simply thought before that the first record would not be the last record, so I thought before that the test_and_set_bit() would not be called when complete() was called. But your reply inspired me and I thought about it carefully and the situation with only one record is possible. I will make version 2 patch to solve this problem. Thanks.
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