[PATCH net v4] bpf, net: Check cgroup_bpf_enabled() only once in do_sock_getsockopt()
Yonghong Song
yonghong.song at linux.dev
Wed Aug 21 11:44:52 PDT 2024
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 at mediatek.com>
> Signed-off-by: Yanghui Li <yanghui.li at mediatek.com>
> Co-developed-by: Cheng-Jui Wang <cheng-jui.wang at mediatek.com>
> Signed-off-by: Cheng-Jui Wang <cheng-jui.wang at mediatek.com>
> Signed-off-by: Tze-nan Wu <Tze-nan.Wu at mediatek.com>
> ---
>
> Chagnes from v1 to v2: https://lore.kernel.org/all/20240819082513.27176-1-Tze-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.
>
> Chagnes from v2 to v3: https://lore.kernel.org/all/20240819155627.1367-1-Tze-nan.Wu@mediatek.com/
> 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@mediatek.com/
> 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;
> }
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