Re: [PATCH v2] net/socket: Check cgroup_bpf_enabled() only once in do_sock_getsockopt

["Tze-nan Wu (吳澤南)" <Tze-nan.Wu@mediatek.com>]

On Mon, 2024-08-19 at 11:18 -0700, Kuniyuki Iwashima wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  From: Tze-nan Wu <Tze-nan.Wu@mediatek.com>
> Date: Mon, 19 Aug 2024 23:56:27 +0800
> > 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@mediatek.com>
> > Signed-off-by: Yanghui Li <yanghui.li@mediatek.com>
> > Co-developed-by: Cheng-Jui Wang <cheng-jui.wang@mediatek.com>
> > Signed-off-by: Cheng-Jui Wang <cheng-jui.wang@mediatek.com>
> > Signed-off-by: Tze-nan Wu <Tze-nan.Wu@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 variable `enabled`.
> `BPF_CGROUP_*`
> >   macros in do_sock_getsockopt can then both check their condition
> with
> >   the same variable, ensuring that either they both passing the
> condition
> >   or both do not.
> > 
> > Appreciate for reviewing this!
> > This patch should make cgroup_bpf_enabled() only using once,
> > but not sure if "BPF_CGROUP_*" is modifiable?(not familiar with
> code here)
> > 
> > If it's not, then maybe I can come up another patch like below one:
> > 	+++ b/net/socket.c
> > 	  	int max_optlen __maybe_unused;
> > 	 	const struct proto_ops *ops;
> > 	 	int err;
> > 	+	bool enabled;
> > 	
> > 	 	err = security_socket_getsockopt(sock, level, optname);
> > 	 	if (err)
> > 	 		return err;
> > 	
> > 	-	if (!compat)
> > 	+	enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> > 	+   if (!compat && enabled)
> > 			max_optlen =
> BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> > 
> > But this will cause do_sock_getsockopt calling cgroup_bpf_enabled
> up to
> > three times , Wondering which approach will be more acceptable?
> > 
> > ---
> >  include/linux/bpf-cgroup.h | 13 ++++++-------
> >  net/socket.c               |  9 ++++++---
> >  2 files changed, 12 insertions(+), 10 deletions(-)
> > 
> > diff --git a/include/linux/bpf-cgroup.h b/include/linux/bpf-
> cgroup.h
> > index fb3c3e7181e6..251632d52fa9 100644
> > --- a/include/linux/bpf-cgroup.h
> > +++ b/include/linux/bpf-cgroup.h
> > @@ -390,20 +390,19 @@ 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)		
> 	       \
> 
> Please keep \ aligned.  Same for other places.
> 
> 
> >  ({									
>        \
> >  	int __ret = 0;							
>        \
> > -	if (cgroup_bpf_enabled(CGROUP_GETSOCKOPT))			
>        \
> 
> Can you assign 'enabled' here to hide its usage in the macro ?

 Hi Kuniyuki,

 No Problem, and thanks for your recommendation.
 Version 3 has hide the cgroup_bpf_enabled in macro,
 and fix the coding sytle issue.

 --Tze-nan
>  
> 
> > +	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 +517,9 @@ 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..5336a2755bb4 100644
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -2365,13 +2365,16 @@ int do_sock_getsockopt(struct socket *sock,
> bool compat, int level,
> >  	int max_optlen __maybe_unused;
> >  	const struct proto_ops *ops;
> >  	int err;
> > +	bool enabled;
> 
> Please keep reverse xmas tree order.
> 
https://docs.kernel.org/process/maintainer-netdev.html#local-variable-ordering-reverse-xmas-tree-rcs
> 
> 
> >  
> >  	err = security_socket_getsockopt(sock, level, optname);
> >  	if (err)
> >  		return err;
> >  
> > -	if (!compat)
> > -		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> > +	if (!compat) {
> > +		enabled = cgroup_bpf_enabled(CGROUP_GETSOCKOPT);
> > +		max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen,
> enabled);
> > +	}
> >  
> >  	ops = READ_ONCE(sock->ops);
> >  	if (level == SOL_SOCKET) {
> > @@ -2390,7 +2393,7 @@ 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
>