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Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Matthias Brugger , AngeloGioacchino Del Regno , Subject: [PATCH net v5] bpf, net: Fix a potential race in do_sock_getsockopt() Date: Fri, 30 Aug 2024 16:25:17 +0800 Message-ID: <20240830082518.23243-1-Tze-nan.Wu@mediatek.com> X-Mailer: git-send-email 2.18.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MTK: N Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" There's a potential race when `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` is false during the execution of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`, but becomes true when `BPF_CGROUP_RUN_PROG_GETSOCKOPT` is called. This inconsistency can lead to `BPF_CGROUP_RUN_PROG_GETSOCKOPT` receiving an "-EFAULT" from `__cgroup_bpf_run_filter_getsockopt(max_optlen=3D0)`. Scenario shown as below: `process A` `process B` ----------- ------------ BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN enable CGROUP_GETSOCKOPT BPF_CGROUP_RUN_PROG_GETSOCKOPT (-EFAULT) To resolve this, remove the `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` macro and directly uses `copy_from_sockptr` to ensure that `max_optlen` is always=20 set before `BPF_CGROUP_RUN_PROG_GETSOCKOPT` is invoked. Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks") Co-developed-by: Yanghui Li Signed-off-by: Yanghui Li Co-developed-by: Cheng-Jui Wang Signed-off-by: Cheng-Jui Wang Signed-off-by: Tze-nan Wu Acked-by: Alexei Starovoitov Acked-by: Stanislav Fomichev --- Changes from v1 to v2: https://lore.kernel.org/all/20240819082513.27176-1-T= ze-nan.Wu@mediatek.com/ Instead of using cgroup_lock in the fastpath, invoke cgroup_bpf_enabled only once and cache the value in the newly added variable `enabled`. `BPF_CGROUP_*` macros in do_sock_getsockopt can then both check their condition with the new variable `enable`, ensuring that either they both passing the condition or both do not. Changes from v2 to v3: https://lore.kernel.org/all/20240819155627.1367-1-Tz= e-nan.Wu@mediatek.com/ Hide cgroup_bpf_enabled in the macro, and some modifications to adapt the coding style. Changes from v3 to v4: https://lore.kernel.org/all/20240820092942.16654-1-T= ze-nan.Wu@mediatek.com/ Add bpf tag to subject, and add the Fixes tag in body. Changes from v4 to v5: https://lore.kernel.org/all/20240821093016.2533-1-Tz= e-nan.Wu@mediatek.com/ Change subject, and fix the race by unconditional `copy_from_sockptr`, instead of adding a new variable. --- include/linux/bpf-cgroup.h | 9 --------- net/socket.c | 4 ++-- 2 files changed, 2 insertions(+), 11 deletions(-) diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h index fb3c3e7181e6..ce91d9b2acb9 100644 --- a/include/linux/bpf-cgroup.h +++ b/include/linux/bpf-cgroup.h @@ -390,14 +390,6 @@ static inline bool cgroup_bpf_sock_enabled(struct sock= *sk, __ret; \ }) =20 -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) \ -({ \ - int __ret =3D 0; \ - if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT)) \ - copy_from_sockptr(&__ret, optlen, sizeof(int)); \ - __ret; \ -}) - #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, optle= n, \ max_optlen, retval) \ ({ \ @@ -518,7 +510,6 @@ static inline int bpf_percpu_cgroup_storage_update(stru= ct bpf_map *map, #define BPF_CGROUP_RUN_PROG_SOCK_OPS(sock_ops) ({ 0; }) #define BPF_CGROUP_RUN_PROG_DEVICE_CGROUP(atype, major, minor, access) ({ = 0; }) #define BPF_CGROUP_RUN_PROG_SYSCTL(head,table,write,buf,count,pos) ({ 0; }) -#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen) ({ 0; }) #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, \ optlen, max_optlen, retval) ({ retval; }) #define BPF_CGROUP_RUN_PROG_GETSOCKOPT_KERN(sock, level, optname, optval, \ diff --git a/net/socket.c b/net/socket.c index fcbdd5bc47ac..0a2bd22ec105 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2362,7 +2362,7 @@ INDIRECT_CALLABLE_DECLARE(bool tcp_bpf_bypass_getsock= opt(int level, int do_sock_getsockopt(struct socket *sock, bool compat, int level, int optname, sockptr_t optval, sockptr_t optlen) { - int max_optlen __maybe_unused; + int max_optlen __maybe_unused =3D 0; const struct proto_ops *ops; int err; =20 @@ -2371,7 +2371,7 @@ int do_sock_getsockopt(struct socket *sock, bool comp= at, int level, return err; =20 if (!compat) - max_optlen =3D BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen); + copy_from_sockptr(&max_optlen, optlen, sizeof(int)); =20 ops =3D READ_ONCE(sock->ops); if (level =3D=3D SOL_SOCKET) { --=20 2.45.2