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([2001:41d0:303:db6b::]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a18bf35930sm390372155e9.13.2026.10.13.16.43.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Oct 2026 16:43:38 -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 3/5] netfilter: nfnetlink_log: pin file with get_file_rcu() before reading f_cred Date: Tue, 13 Oct 2026 23:43:26 +0000 Message-ID: <20261013234329.2797868-4-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 NFLOG UID/GID metadata construction reads file->f_cred without pinning the file, which could lead to logging credentials from an unrelated file if the slab slot is reused. Use get_file_rcu() to take a reference on the file before reading credentials, and fput() to release it after extracting uid/gid values. Fixes: 0ede61d8589cc ("file: convert to SLAB_TYPESAFE_BY_RCU") Cc: stable@vger.kernel.org Signed-off-by: Tristan Madani --- net/netfilter/nfnetlink_log.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c index d923f2cb13980..8c9e297a7dc18 100644 --- a/net/netfilter/nfnetlink_log.c +++ b/net/netfilter/nfnetlink_log.c @@ -632,22 +632,27 @@ __build_packet_message(struct nfnl_log_net *log, /* UID */ sk = skb->sk; if (sk && sk_fullsock(sk)) { - const struct socket *sock; - const struct file *file; + struct socket *sock; + struct file *file; /* 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. + * 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) { const struct cred *cred = file->f_cred; struct user_namespace *user_ns = inst->peer_user_ns; __be32 uid = htonl(from_kuid_munged(user_ns, cred->fsuid)); __be32 gid = htonl(from_kgid_munged(user_ns, cred->fsgid)); + fput(file); if (nla_put_be32(inst->skb, NFULA_UID, uid) || nla_put_be32(inst->skb, NFULA_GID, gid)) goto nla_put_failure; -- 2.47.3