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 <andriin@fb.com>
Cc: Martin Lau <kafai@fb.com>
Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
diff --git a/net/socket.c b/net/socket.c
index 963df5d..0ddfbfb 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);
}