On 8/21/24 2:30 AM, Tze-nan Wu wrote:
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.
Fixes: 0d01da6afc54 ("bpf: implement getsockopt and setsockopt hooks")
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.
Chagnes from v3 to v4: https://lore.kernel.org/all/20240820092942.16654-1-Tze-nan.Wu@xxxxxxxxxxxx/
Add bpf tag to subject, and Fixes tag in body.
---
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);
Here, 'enabled' is actually assigned with a value in the macro. I am not sure
whether this is a common practice or not. At least from macro, it is not clear
about this.
Maybe we can do
max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen, &enabled);
The &enabled signals that its value could change. And indeed
the macro will store the proper value to &enabled properly.
Just my 2 cents.
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;
}
