From: Jann Horn <firstname.lastname@example.org> To: Sargun Dhillon <email@example.com> Cc: Kees Cook <firstname.lastname@example.org>, kernel list <email@example.com>, Tycho Andersen <firstname.lastname@example.org>, Aleksa Sarai <email@example.com>, Christian Brauner <firstname.lastname@example.org>, Linux Containers <email@example.com>, Linux API <firstname.lastname@example.org> Subject: Re: [RFC PATCH] seccomp: Add extensibility mechanism to read notifications Date: Mon, 15 Jun 2020 11:36:22 +0200 [thread overview] Message-ID: <CAG48ez2ZyYkHhbuwLYehR5fx2_d9yoVg4tBmyqvVqpy-oZ-0cA@mail.gmail.com> (raw) In-Reply-To: <email@example.com> On Sat, Jun 13, 2020 at 9:26 AM Sargun Dhillon <firstname.lastname@example.org> 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. This extensible struct > is slightly misleading 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?
next prev parent reply other threads:[~2020-06-15 9:36 UTC|newest] Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-06-13 7:26 Sargun Dhillon 2020-06-15 9:36 ` Jann Horn [this message] 2020-06-16 5:12 ` Sargun Dhillon 2020-06-15 13:44 ` Tycho Andersen 2020-06-15 18:26 ` Kees Cook
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