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([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a18bf35930sm390372155e9.13.2026.10.13.16.43.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 16:43:37 -0700 (PDT) From: Tristan Madani To: Pablo Neira Ayuso , Florian Westphal Cc: Phil Sutter , Christian Brauner , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netfilter-devel@vger.kernel.org, coreteam@netfilter.org, netdev@vger.kernel.org, Tristan Madani , stable@vger.kernel.org Subject: [PATCH nf 2/5] netfilter: nft_meta: pin file with get_file_rcu() before reading f_cred Date: Tue, 13 Oct 2026 23:43:25 +0000 Message-ID: <20261013234329.2797868-3-tristmd@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20261013234329.2797868-1-tristmd@gmail.com> References: <20261013234329.2797868-1-tristmd@gmail.com> Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Tristan Madani Since commit 0ede61d8589cc ("file: convert to SLAB_TYPESAFE_BY_RCU"), struct file objects can have their slab slot reused while RCU readers still hold pointers to them. The nft_meta skuid/skgid evaluation reads file->f_cred to extract fsuid/fsgid without pinning the file. If the file is freed and the slab slot is reused, the credential data may belong to a different file. Use get_file_rcu() to take a reference on the file before accessing its credentials, and fput() to release it afterward. Fixes: 0ede61d8589cc ("file: convert to SLAB_TYPESAFE_BY_RCU") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- net/netfilter/nft_meta.c | 19 ++++++++++++------- 1 file changed, 12 insertions(+), 7 deletions(-) diff --git a/net/netfilter/nft_meta.c b/net/netfilter/nft_meta.c index 01cfbaa365250..069c01a71df16 100644 --- a/net/netfilter/nft_meta.c +++ b/net/netfilter/nft_meta.c @@ -135,19 +135,23 @@ nft_meta_get_eval_skugid(enum nft_meta_keys key, const struct nft_pktinfo *pkt) { const struct sock *sk = skb_to_full_sk(pkt->skb); - const struct socket *sock; - const struct file *file; + struct socket *sock; + struct file *file; if (!sk || !sk_fullsock(sk) || !net_eq(nft_net(pkt), sock_net(sk))) return false; - /* The sk pointer remains valid as long as the skb is. The sk_socket and - * file pointer may become NULL if the socket is closed. Both structures - * (including file->cred) are RCU freed which means they can be accessed - * within a RCU read section. + /* The sk pointer remains valid as long as the skb is. The + * sk_socket and file pointer may become NULL if the socket is + * closed. Since struct file uses SLAB_TYPESAFE_BY_RCU, pin the + * file with get_file_rcu() to ensure f_cred is not from a + * reused slab slot. */ sock = READ_ONCE(sk->sk_socket); - file = sock ? READ_ONCE(sock->file) : NULL; + if (sock) + file = get_file_rcu(&sock->file); + else + file = NULL; if (!file) return false; @@ -164,6 +168,7 @@ nft_meta_get_eval_skugid(enum nft_meta_keys key, break; } + fput(file); return true; } -- 2.47.3