From 0d01da6afc5402f60325c5da31b22f7d56689b49 Mon Sep 17 00:00:00 2001 From: Stanislav Fomichev Date: Thu, 27 Jun 2019 13:38:47 -0700 Subject: bpf: implement getsockopt and setsockopt hooks Implement new BPF_PROG_TYPE_CGROUP_SOCKOPT program type and BPF_CGROUP_{G,S}ETSOCKOPT cgroup hooks. BPF_CGROUP_SETSOCKOPT can modify user setsockopt arguments before passing them down to the kernel or bypass kernel completely. BPF_CGROUP_GETSOCKOPT can can inspect/modify getsockopt arguments that kernel returns. Both hooks reuse existing PTR_TO_PACKET{,_END} infrastructure. The buffer memory is pre-allocated (because I don't think there is a precedent for working with __user memory from bpf). This might be slow to do for each {s,g}etsockopt call, that's why I've added __cgroup_bpf_prog_array_is_empty that exits early if there is nothing attached to a cgroup. Note, however, that there is a race between __cgroup_bpf_prog_array_is_empty and BPF_PROG_RUN_ARRAY where cgroup program layout might have changed; this should not be a problem because in general there is a race between multiple calls to {s,g}etsocktop and user adding/removing bpf progs from a cgroup. The return code of the BPF program is handled as follows: * 0: EPERM * 1: success, continue with next BPF program in the cgroup chain v9: * allow overwriting setsockopt arguments (Alexei Starovoitov): * use set_fs (same as kernel_setsockopt) * buffer is always kzalloc'd (no small on-stack buffer) v8: * use s32 for optlen (Andrii Nakryiko) v7: * return only 0 or 1 (Alexei Starovoitov) * always run all progs (Alexei Starovoitov) * use optval=0 as kernel bypass in setsockopt (Alexei Starovoitov) (decided to use optval=-1 instead, optval=0 might be a valid input) * call getsockopt hook after kernel handlers (Alexei Starovoitov) v6: * rework cgroup chaining; stop as soon as bpf program returns 0 or 2; see patch with the documentation for the details * drop Andrii's and Martin's Acked-by (not sure they are comfortable with the new state of things) v5: * skip copy_to_user() and put_user() when ret == 0 (Martin Lau) v4: * don't export bpf_sk_fullsock helper (Martin Lau) * size != sizeof(__u64) for uapi pointers (Martin Lau) * offsetof instead of bpf_ctx_range when checking ctx access (Martin Lau) v3: * typos in BPF_PROG_CGROUP_SOCKOPT_RUN_ARRAY comments (Andrii Nakryiko) * reverse christmas tree in BPF_PROG_CGROUP_SOCKOPT_RUN_ARRAY (Andrii Nakryiko) * use __bpf_md_ptr instead of __u32 for optval{,_end} (Martin Lau) * use BPF_FIELD_SIZEOF() for consistency (Martin Lau) * new CG_SOCKOPT_ACCESS macro to wrap repeated parts v2: * moved bpf_sockopt_kern fields around to remove a hole (Martin Lau) * aligned bpf_sockopt_kern->buf to 8 bytes (Martin Lau) * bpf_prog_array_is_empty instead of bpf_prog_array_length (Martin Lau) * added [0,2] return code check to verifier (Martin Lau) * dropped unused buf[64] from the stack (Martin Lau) * use PTR_TO_SOCKET for bpf_sockopt->sk (Martin Lau) * dropped bpf_target_off from ctx rewrites (Martin Lau) * use return code for kernel bypass (Martin Lau & Andrii Nakryiko) Cc: Andrii Nakryiko Cc: Martin Lau Signed-off-by: Stanislav Fomichev Signed-off-by: Alexei Starovoitov --- net/socket.c | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) (limited to 'net/socket.c') diff --git a/net/socket.c b/net/socket.c index 963df5dbdd54..0ddfbfb761d9 100644 --- a/net/socket.c +++ b/net/socket.c @@ -2051,6 +2051,8 @@ SYSCALL_DEFINE4(recv, int, fd, void __user *, ubuf, size_t, size, static int __sys_setsockopt(int fd, int level, int optname, char __user *optval, int optlen) { + mm_segment_t oldfs = get_fs(); + char *kernel_optval = NULL; int err, fput_needed; struct socket *sock; @@ -2063,6 +2065,22 @@ static int __sys_setsockopt(int fd, int level, int optname, if (err) goto out_put; + err = BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock->sk, &level, + &optname, optval, &optlen, + &kernel_optval); + + if (err < 0) { + goto out_put; + } else if (err > 0) { + err = 0; + goto out_put; + } + + if (kernel_optval) { + set_fs(KERNEL_DS); + optval = (char __user __force *)kernel_optval; + } + if (level == SOL_SOCKET) err = sock_setsockopt(sock, level, optname, optval, @@ -2071,6 +2089,11 @@ static int __sys_setsockopt(int fd, int level, int optname, err = sock->ops->setsockopt(sock, level, optname, optval, optlen); + + if (kernel_optval) { + set_fs(oldfs); + kfree(kernel_optval); + } out_put: fput_light(sock->file, fput_needed); } @@ -2093,6 +2116,7 @@ static int __sys_getsockopt(int fd, int level, int optname, { int err, fput_needed; struct socket *sock; + int max_optlen; sock = sockfd_lookup_light(fd, &err, &fput_needed); if (sock != NULL) { @@ -2100,6 +2124,8 @@ static int __sys_getsockopt(int fd, int level, int optname, if (err) goto out_put; + max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen); + if (level == SOL_SOCKET) err = sock_getsockopt(sock, level, optname, optval, @@ -2108,6 +2134,10 @@ static int __sys_getsockopt(int fd, int level, int optname, err = sock->ops->getsockopt(sock, level, optname, optval, optlen); + + err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname, + optval, optlen, + max_optlen, err); out_put: fput_light(sock->file, fput_needed); } -- cgit v1.2.3