Re: [PATCH v3 8/9] io_uring/cmd: BPF hook for getsockopt cmd

Martin KaFai Lau <martin.lau@xxxxxxxxx> · Mon, 21 Aug 2023 13:25:25 -0700

On 8/17/23 12:08 PM, Gabriel Krisman Bertazi wrote:
Breno Leitao <leitao@xxxxxxxxxx> writes:

Add BPF hook support for getsockopts io_uring command. So, BPF cgroups
programs can run when SOCKET_URING_OP_GETSOCKOPT command is executed
through io_uring.

This implementation follows a similar approach to what
__sys_getsockopt() does, but, using USER_SOCKPTR() for optval instead of
kernel pointer.

Signed-off-by: Breno Leitao <leitao@xxxxxxxxxx>
---
  io_uring/uring_cmd.c | 18 +++++++++++++-----
  1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index a567dd32df00..9e08a14760c3 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -5,6 +5,8 @@
  #include <linux/io_uring.h>
  #include <linux/security.h>
  #include <linux/nospec.h>
+#include <linux/compat.h>
+#include <linux/bpf-cgroup.h>
  
  #include <uapi/linux/io_uring.h>
  #include <uapi/asm-generic/ioctls.h>
@@ -184,17 +186,23 @@ static inline int io_uring_cmd_getsockopt(struct socket *sock,
  	if (err)
  		return err;
  
-	if (level == SOL_SOCKET) {
+	err = -EOPNOTSUPP;
+	if (level == SOL_SOCKET)
  		err = sk_getsockopt(sock->sk, level, optname,
  				    USER_SOCKPTR(optval),
  				    KERNEL_SOCKPTR(&optlen));
-		if (err)
-			return err;
  
+	if (!(issue_flags & IO_URING_F_COMPAT))
+		err = BPF_CGROUP_RUN_PROG_GETSOCKOPT(sock->sk, level,
+						     optname,
+						     USER_SOCKPTR(optval),
+						     KERNEL_SOCKPTR(&optlen),
+						     optlen, err);
+
+	if (!err)
  		return optlen;
-	}

Shouldn't you call sock->ops->getsockopt for level!=SOL_SOCKET prior to
running the hook?  Before this patch, it would bail out with EOPNOTSUPP,
but now the bpf hook gets called even for level!=SOL_SOCKET, which
doesn't fit __sys_getsockopt. Am I misreading the code?
I agree it should not call into bpf if the io_uring cannot support non 
SOL_SOCKET optnames. Otherwise, the bpf prog will get different optval and 
optlen when running in _sys_getsockopt vs io_uring getsockopt (e.g. in regular 
_sys_getsockopt(SOL_TCP), bpf expects the optval returned from tcp_getsockopt).

I think __sys_getsockopt can also be refactored similar to __sys_setsockopt in 
patch 3. Yes, for non SOL_SOCKET it only supports __user *optval and __user 
*optlen but may be a WARN_ON_ONCE/BUG_ON(sockpt_is_kernel(optval)) can be added 
before calling ops->getsockopt()? Then this details can be hidden away from the 
io_uring.








