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Wed, 11 Nov 2026 07:31:16 -0800 (PST) Received: from localhost.localdomain ([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4bb4c5e2fd6sm2261365e9.10.2026.11.11.07.31.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Nov 2026 07:31:15 -0800 (PST) From: Tristan Madani To: Jamal Hadi Salim , Jiri Pirko Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Christian Brauner , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org, Tristan Madani Subject: [PATCH net] net/sched: cls_flow: pin file with get_file_rcu before reading f_cred Date: Wed, 11 Nov 2026 15:31:06 +0000 Message-ID: <20261111153106.580776-1-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani flow_get_skuid() and flow_get_skgid() read sk->sk_socket->file->f_cred without holding a reference to the file. Since the file slab uses SLAB_TYPESAFE_BY_RCU, a concurrent close() may free and recycle the file object, causing stale credential data to be read through f_cred. Pin the file with get_file_rcu() before accessing its credentials and release with fput() afterwards. Fixes: 0ede61d8589cc ("file: convert to SLAB_TYPESAFE_BY_RCU") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- net/sched/cls_flow.c | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) diff --git a/net/sched/cls_flow.c b/net/sched/cls_flow.c index a9ac3acf6eda0..233ca13299930 100644 --- a/net/sched/cls_flow.c +++ b/net/sched/cls_flow.c @@ -17,6 +17,7 @@ #include #include #include +#include #include #include @@ -208,10 +209,16 @@ static u32 flow_get_rtclassid(const struct sk_buff *skb) static u32 flow_get_skuid(const struct sk_buff *skb) { struct sock *sk = skb_to_full_sk(skb); + struct file *filp; - if (sk && sk->sk_socket && sk->sk_socket->file) { - kuid_t skuid = sk->sk_socket->file->f_cred->fsuid; + if (!sk || !sk->sk_socket) + return 0; + + filp = get_file_rcu(&sk->sk_socket->file); + if (filp) { + kuid_t skuid = filp->f_cred->fsuid; + fput(filp); return from_kuid(&init_user_ns, skuid); } return 0; @@ -220,10 +227,16 @@ static u32 flow_get_skuid(const struct sk_buff *skb) static u32 flow_get_skgid(const struct sk_buff *skb) { struct sock *sk = skb_to_full_sk(skb); + struct file *filp; + + if (!sk || !sk->sk_socket) + return 0; - if (sk && sk->sk_socket && sk->sk_socket->file) { - kgid_t skgid = sk->sk_socket->file->f_cred->fsgid; + filp = get_file_rcu(&sk->sk_socket->file); + if (filp) { + kgid_t skgid = filp->f_cred->fsgid; + fput(filp); return from_kgid(&init_user_ns, skgid); } return 0; -- 2.47.3