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([147.46.174.222]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-8455366ec53sm2844747b3a.13.2026.06.19.08.03.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2026 08:03:55 -0700 (PDT) From: Sechang Lim To: "D . Wythe" , Dust Li , Sidraya Jayagond , Wenjia Zhang , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni Cc: Mahanta Jambigi , Tony Lu , Wen Gu , Simon Horman , Ursula Braun , Karsten Graul , Guvenc Gulce , linux-rdma@vger.kernel.org, linux-s390@vger.kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: [PATCH net v2] net/smc: fix out-of-bounds read when sk_user_data holds a sk_psock Date: Fri, 19 Jun 2026 15:03:41 +0000 Message-ID: <20260619150342.3626224-1-rhkrqnwk98@gmail.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit SMC stores its smc_sock in the clcsock's sk_user_data tagged SK_USER_DATA_NOCOPY and reads it back with smc_clcsock_user_data(), which only strips that flag. sockmap stores a sk_psock in the same field tagged SK_USER_DATA_NOCOPY | SK_USER_DATA_PSOCK. Nothing keeps both off one socket, and SMC then casts the sk_psock to an smc_sock. A passive-open child hits this. It inherits the listener's smc_clcsock_data_ready(), but sk_clone_lock() clears its NOCOPY sk_user_data, and a BPF sock_ops program then adds the child to a sockmap, installing a sk_psock in that field. The inherited callback reads it as an smc_sock and dereferences a clcsk_* pointer past the end of the sk_psock: BUG: KASAN: slab-out-of-bounds in smc_clcsock_data_ready+0x84/0x200 net/smc/af_smc.c:2637 Read of size 8 at addr ffff8880013b8674 by task syz.6.12484/67930 smc_clcsock_data_ready+0x84/0x200 net/smc/af_smc.c:2637 tcp_urg+0x24d/0x360 net/ipv4/tcp_input.c:6264 tcp_rcv_state_process+0x280d/0x4940 net/ipv4/tcp_input.c:7336 tcp_child_process+0x371/0xa50 net/ipv4/tcp_minisocks.c:1002 tcp_v4_rcv+0x1eaa/0x2a00 net/ipv4/tcp_ipv4.c:2186 [...] Allocated by task 67930: sk_psock_init+0x142/0x740 net/core/skmsg.c:766 sock_hash_update_common+0xd3/0x990 net/core/sock_map.c:1010 bpf_sock_hash_update+0x114/0x170 net/core/sock_map.c:1229 __cgroup_bpf_run_filter_sock_ops+0x74/0xa0 kernel/bpf/cgroup.c:1727 tcp_init_transfer+0x1085/0x1100 net/ipv4/tcp_input.c:6693 [...] sk_psock() already guards the other side, returning NULL unless SK_USER_DATA_PSOCK is set. Make smc_clcsock_user_data() and its RCU variant return the smc_sock only when sk_user_data carries SMC's tag alone. A sk_psock then reads back as NULL, which the data_ready and fallback callbacks already handle. Fixes: a60a2b1e0af1 ("net/smc: reduce active tcp_listen workers") Signed-off-by: Sechang Lim --- net/smc/smc.h | 18 +++++++++++++++--- 1 file changed, 15 insertions(+), 3 deletions(-) diff --git a/net/smc/smc.h b/net/smc/smc.h index 52145df83f6e..88dfb459b7cc 100644 --- a/net/smc/smc.h +++ b/net/smc/smc.h @@ -342,13 +342,25 @@ static inline void smc_init_saved_callbacks(struct smc_sock *smc) static inline struct smc_sock *smc_clcsock_user_data(const struct sock *clcsk) { - return (struct smc_sock *) - ((uintptr_t)clcsk->sk_user_data & ~SK_USER_DATA_NOCOPY); + uintptr_t data = (uintptr_t)clcsk->sk_user_data; + + /* + * Return the smc_sock only if the slot carries SMC's tag alone. + * sockmap stores a sk_psock here tagged SK_USER_DATA_PSOCK; it is + * not an smc_sock and must not be dereferenced as one. + */ + if ((data & ~SK_USER_DATA_PTRMASK) != SK_USER_DATA_NOCOPY) + return NULL; + return (struct smc_sock *)(data & SK_USER_DATA_PTRMASK); } static inline struct smc_sock *smc_clcsock_user_data_rcu(const struct sock *clcsk) { - return (struct smc_sock *)rcu_dereference_sk_user_data(clcsk); + uintptr_t data = (uintptr_t)rcu_dereference(__sk_user_data(clcsk)); + + if ((data & ~SK_USER_DATA_PTRMASK) != SK_USER_DATA_NOCOPY) + return NULL; + return (struct smc_sock *)(data & SK_USER_DATA_PTRMASK); } /* save target_cb in saved_cb, and replace target_cb with new_cb */ -- 2.43.0