Re: [PATCH] net/tls: fix use-after-free in -EBUSY error path of tls_do_encryption

[Sabrina Dubroca <sd@queasysnail.net>]

2026-04-03, 09:36:17 +0800, Muhammad Alifa Ramdhan wrote:
> The -EBUSY handling in tls_do_encryption(), introduced by commit
> 859054147318 ("net: tls: handle backlogging of crypto requests"), has
> a use-after-free due to double cleanup of encrypt_pending and the
> scatterlist entry.
> 
> When crypto_aead_encrypt() returns -EBUSY, the request is enqueued to
> the cryptd backlog and the async callback tls_encrypt_done() will be
> invoked upon completion. That callback unconditionally restores the
> scatterlist entry (sge->offset, sge->length) and decrements
> ctx->encrypt_pending. However, if tls_encrypt_async_wait() returns an
> error, the synchronous error path in tls_do_encryption() performs the
> same cleanup again, double-decrementing encrypt_pending and
> double-restoring the scatterlist.
> 
> The double-decrement corrupts the encrypt_pending sentinel (initialized
> to 1), making tls_encrypt_async_wait() permanently skip the wait for
> pending async callbacks. A subsequent sendmsg can then free the
> tls_rec via bpf_exec_tx_verdict() while a cryptd callback is still
> pending, resulting in a use-after-free when the callback fires on the
> freed record.
> 
> Fix this by skipping the synchronous cleanup when the -EBUSY async
> wait returns an error, since the callback has already handled
> encrypt_pending and sge restoration.
> 
> Fixes: 859054147318 ("net: tls: handle backlogging of crypto requests")
> Cc: stable@vger.kernel.org
> Signed-off-by: Muhammad Alifa Ramdhan <ramdhan@starlabs.sg>
> ---
>  net/tls/tls_sw.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>

-- 
Sabrina