[PATCH v3] net/socket: Check cgroup_bpf_enabled() only once in do_sock_getsockopt()

[Tze-nan Wu]

The return value from `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` can change
between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
`BPF_CGROUP_RUN_PROG_GETSOCKOPT`.

If `cgroup_bpf_enabled(CGROUP_GETSOCKOPT)` changes from "false" to
"true" between the invocations of `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN` and
`BPF_CGROUP_RUN_PROG_GETSOCKOPT`, `BPF_CGROUP_RUN_PROG_GETSOCKOPT` will
receive an -EFAULT from `__cgroup_bpf_run_filter_getsockopt(max_optlen=0)`
due to `get_user()` was not reached in `BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN`.

Scenario shown as below:

           `process A`                      `process B`
           -----------                      ------------
  BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN
                                            enable CGROUP_GETSOCKOPT
  BPF_CGROUP_RUN_PROG_GETSOCKOPT (-EFAULT)

To prevent this, invoke `cgroup_bpf_enabled()` only once and cache the
result in a newly added local variable `enabled`.
Both `BPF_CGROUP_*` macros in `do_sock_getsockopt` will then check their
condition using the same `enabled` variable as the condition variable,
instead of using the return values from `cgroup_bpf_enabled` called by
themselves as the condition variable(which could yield different results).
This ensures that either both `BPF_CGROUP_*` macros pass the condition
or neither does.

Co-developed-by: Yanghui Li <yanghui.li@xxxxxxxxxxxx>
Signed-off-by: Yanghui Li <yanghui.li@xxxxxxxxxxxx>
Co-developed-by: Cheng-Jui Wang <cheng-jui.wang@xxxxxxxxxxxx>
Signed-off-by: Cheng-Jui Wang <cheng-jui.wang@xxxxxxxxxxxx>
Signed-off-by: Tze-nan Wu <Tze-nan.Wu@xxxxxxxxxxxx>
---

Chagnes from v1 to v2: https://lore.kernel.org/all/20240819082513.27176-1-Tze-nan.Wu@xxxxxxxxxxxx/
  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.

Chagnes from v2 to v3: https://lore.kernel.org/all/20240819155627.1367-1-Tze-nan.Wu@xxxxxxxxxxxx/
  Hide cgroup_bpf_enabled in the macro, and some modifications to adapt
  the coding style.

---
 include/linux/bpf-cgroup.h | 15 ++++++++-------
 net/socket.c               |  5 +++--
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-cgroup.h
index fb3c3e7181e6..5afa2ac76aae 100644
--- a/include/linux/bpf-cgroup.h
+++ b/include/linux/bpf-cgroup.h
@@ -390,20 +390,20 @@ static inline bool cgroup_bpf_sock_enabled(struct sock *sk,
 	__ret;								       \
 })
 
-#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen)			       \
+#define BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled)		       \
 ({									       \
 	int __ret = 0;							       \
-	if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))			       \
+	enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);		       \
+	if (enabled)							       \
 		copy_from_sockptr(&__ret, optlen, sizeof(int));		       \
 	__ret;								       \
 })
 
 #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, optlen,   \
-				       max_optlen, retval)		       \
+				       max_optlen, retval, enabled)	       \
 ({									       \
 	int __ret = retval;						       \
-	if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT) &&			       \
-	    cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))		       \
+	if (enabled && cgroup_bpf_sock_enabled(sock, CGROUP_GETSOCKOPT))       \
 		if (!(sock)->sk_prot->bpf_bypass_getsockopt ||		       \
 		    !INDIRECT_CALL_INET_1((sock)->sk_prot->bpf_bypass_getsockopt, \
 					tcp_bpf_bypass_getsockopt,	       \
@@ -518,9 +518,10 @@ static inline int bpf_percpu_cgroup_storage_update(struct 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_GETSOCKOPT_MAX_OPTLEN(optlen, enabled) ({ 0; })
 #define BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock, level, optname, optval, \
-				       optlen, max_optlen, retval) ({ retval; })
+				       optlen, max_optlen, retval, \
+				       enabled) ({ retval; })
 #define BPF_CGROUP_RUN_PROG_GETSOCKOPT_KERN(sock, level, optname, optval, \
 					    optlen, retval) ({ retval; })
 #define BPF_CGROUP_RUN_PROG_SETSOCKOPT(sock, level, optname, optval, optlen, \
diff --git a/net/socket.c b/net/socket.c
index fcbdd5bc47ac..0b465dc8a789 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2363,6 +2363,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 		       int optname, sockptr_t optval, sockptr_t optlen)
 {
 	int max_optlen __maybe_unused;
+	bool enabled __maybe_unused;
 	const struct proto_ops *ops;
 	int err;
 
@@ -2371,7 +2372,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 		return err;
 
 	if (!compat)
-		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
+		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, enabled);
 
 	ops = READ_ONCE(sock->ops);
 	if (level == SOL_SOCKET) {
@@ -2390,7 +2391,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
 	if (!compat)
 		err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level, optname,
 						     optval, optlen, max_optlen,
-						     err);
+						     err, enabled);
 
 	return err;
 }
-- 
2.45.2