On Sat, Jun 13, 2020 at 9:26 AM Sargun Dhillon <sargun@xxxxxxxxx> wrote: > This introduces an extensibility mechanism to receive seccomp > notifications. It uses read(2), as opposed to using an ioctl. The listener > must be first configured to write the notification via the > SECCOMP_IOCTL_NOTIF_CONFIG ioctl with the fields that the user is > interested in. > > This is different than the old SECCOMP_IOCTL_NOTIF_RECV method as it allows > for more flexibility. It allows the user to opt into certain fields, and > not others. This is nice for users who want to opt into some fields like > thread group leader. In the future, this mechanism can be used to expose > file descriptors to users, Please don't touch the caller's file descriptor table from read/write handlers, only from ioctl handlers. A process should always be able to read from files supplied by an untrusted user without having to worry about new entries mysteriously popping up in its fd table. > such as a representation of the process's > memory. It also has good forwards and backwards compatibility guarantees. > Users with programs compiled against newer headers will work fine on older > kernels as long as they don't opt into any sizes, or optional fields that > are only available on newer kernels. > > The ioctl method relies on an extensible struct[1]. This extensible struct > is slightly misleading[2] as the ioctl number changes when we extend it. > This breaks backwards compatibility with older kernels even if we're not > asking for any fields that we do not need. In order to deal with this, the > ioctl number would need to be dynamic, or the user would need to pass the > size they're expecting, and we would need to implemented "extended syscall" > semantics in ioctl. This potentially causes issue to future work of > kernel-assisted copying for ioctl user buffers. I don't see the issue. Can't you replace "switch (cmd)" with "switch (cmd & ~IOCSIZE_MASK)" and then check the size separately? _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
