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SubjectRe: [PATCH v3 8/9] io_uring/cmd: BPF hook for getsockopt cmd
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On 8/17/23 12:08 PM, Gabriel Krisman Bertazi wrote:
> Breno Leitao <leitao@debian.org> 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@debian.org>
>> ---
>> 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.

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