linux-kernel - Re: [PATCH] smb: client: fix use-after-free in crypt

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Message-ID: <bb5dba5b431172ae8b268470d6e37419@manguebit.org>
Date: Thu, 10 Jul 2025 20:18:15 -0300
From: Paulo Alcantara <pc@...guebit.org>
To: Wang Zhaolong <wangzhaolong@...weicloud.com>, sfrench@...ba.org,
 ematsumiya@...e.de
Cc: linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
 linux-kernel@...r.kernel.org, wangzhaolong1@...wei.com,
 yi.zhang@...wei.com, yangerkun@...wei.com, chengzhihao1@...wei.com
Subject: Re: [PATCH] smb: client: fix use-after-free in crypt_message when
 using async crypto

Wang Zhaolong <wangzhaolong@...weicloud.com> writes:

> The CVE-2024-50047 fix removed asynchronous crypto handling from
> crypt_message(), assuming all crypto operations are synchronous.
> However, when hardware crypto accelerators are used, this can cause
> use-after-free crashes:
>
>   crypt_message()
>     // Allocate the creq buffer containing the req
>     creq = smb2_get_aead_req(..., &req);
>
>     // Async encryption returns -EINPROGRESS immediately
>     rc = enc ? crypto_aead_encrypt(req) : crypto_aead_decrypt(req);
>
>     // Free creq while async operation is still in progress
>     kvfree_sensitive(creq, ...);
>
> Hardware crypto modules often implement async AEAD operations for
> performance. When crypto_aead_encrypt/decrypt() returns -EINPROGRESS,
> the operation completes asynchronously. Without crypto_wait_req(),
> the function immediately frees the request buffer, leading to crashes
> when the driver later accesses the freed memory.
>
> This results in a use-after-free condition when the hardware crypto
> driver later accesses the freed request structure, leading to kernel
> crashes with NULL pointer dereferences.
>
> The issue occurs because crypto_alloc_aead() with mask=0 doesn't
> guarantee synchronous operation. Even without CRYPTO_ALG_ASYNC in
> the mask, async implementations can be selected.
>
> Fix by restoring the async crypto handling:
> - DECLARE_CRYPTO_WAIT(wait) for completion tracking
> - aead_request_set_callback() for async completion notification
> - crypto_wait_req() to wait for operation completion
>
> This ensures the request buffer isn't freed until the crypto operation
> completes, whether synchronous or asynchronous, while preserving the
> CVE-2024-50047 fix.
>
> Fixes: b0abcd65ec54 ("smb: client: fix UAF in async decryption")
> Link: https://lore.kernel.org/all/8b784a13-87b0-4131-9ff9-7a8993538749@huaweicloud.com/
> Cc: stable@...r.kernel.org
> Signed-off-by: Wang Zhaolong <wangzhaolong@...weicloud.com>
> ---
>  fs/smb/client/smb2ops.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)

Reviewed-by: Paulo Alcantara (Red Hat) <pc@...guebit.org>