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Message-ID: <VI1P193MB0752C1A213A65CD7D49347B399D6A@VI1P193MB0752.EURP193.PROD.OUTLOOK.COM> Date: Tue, 17 Oct 2023 18:25:12 +0800 From: Juntong Deng <juntong.deng@...look.com> To: Simon Horman <horms@...nel.org> Cc: borisp@...dia.com, john.fastabend@...il.com, kuba@...nel.org, davem@...emloft.net, edumazet@...gle.com, pabeni@...hat.com, netdev@...r.kernel.org, linux-kernel@...r.kernel.org, linux-kernel-mentees@...ts.linuxfoundation.org, syzbot+29c22ea2d6b2c5fd2eae@...kaller.appspotmail.com Subject: Re: [PATCH] net/tls: Fix slab-use-after-free in tls_encrypt_done On 2023/10/16 17:50, Simon Horman wrote: > On Thu, Oct 12, 2023 at 07:02:51PM +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 > > Hi Juntong Deng, > > I'm slightly confused by "causes tls_sw_release_resources_tx to continue > executing". > > What I see in tls_sw_release_resources_tx() is: > > /* Wait for any pending async encryptions to complete */ > spin_lock_bh(&ctx->encrypt_compl_lock); > ctx->async_notify = true; > pending = atomic_read(&ctx->encrypt_pending); > spin_unlock_bh(&ctx->encrypt_compl_lock); > > Am I wrong in thinking the above will block because > (the same) ctx->encrypt_compl_lock is held in tls_encrypt_done? > Hi Simon Horman, What I mean is that tls_sw_release_resources_tx will pause at crypto_wait_req(-EINPROGRESS, &ctx->async_wait) because crypto_wait_req call wait_for_completion. Then after tls_encrypt_done call complete(&ctx->async_wait.completion), it will cause tls_sw_release_resources_tx to continue executing. >> 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> >> --- >> net/tls/tls_sw.c | 6 ++++-- >> 1 file changed, 4 insertions(+), 2 deletions(-) >> >> diff --git a/net/tls/tls_sw.c b/net/tls/tls_sw.c >> index 270712b8d391..7abe5a6aa989 100644 >> --- a/net/tls/tls_sw.c >> +++ b/net/tls/tls_sw.c >> @@ -441,6 +441,7 @@ static void tls_encrypt_done(void *data, int err) >> struct sk_msg *msg_en; >> bool ready = false; >> struct sock *sk; >> + int async_notify; >> int pending; >> >> msg_en = &rec->msg_encrypted; >> @@ -482,10 +483,11 @@ static void tls_encrypt_done(void *data, int err) >> >> spin_lock_bh(&ctx->encrypt_compl_lock); >> pending = atomic_dec_return(&ctx->encrypt_pending); >> + async_notify = ctx->async_notify; >> + spin_unlock_bh(&ctx->encrypt_compl_lock); >> >> - if (!pending && ctx->async_notify) >> + if (!pending && async_notify) >> complete(&ctx->async_wait.completion); >> - spin_unlock_bh(&ctx->encrypt_compl_lock); >> >> if (!ready) >> return; >> -- >> 2.39.2 >> >>
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