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Date: Thu, 11 Jun 2020 16:23:10 -0700 From: Kees Cook <keescook@...omium.org> To: Sargun Dhillon <sargun@...gun.me> Cc: Christian Brauner <christian.brauner@...ntu.com>, containers@...ts.linux-foundation.org, Giuseppe Scrivano <gscrivan@...hat.com>, Robert Sesek <rsesek@...gle.com>, Chris Palmer <palmer@...gle.com>, Jann Horn <jannh@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Daniel Wagner <daniel.wagner@...-carit.de>, linux-kernel@...r.kernel.org, Matt Denton <mpdenton@...gle.com>, John Fastabend <john.r.fastabend@...el.com>, linux-fsdevel@...r.kernel.org, Tejun Heo <tj@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, cgroups@...r.kernel.org, stable@...r.kernel.org, "David S . Miller" <davem@...emloft.net> Subject: Re: [PATCH v3 1/4] fs, net: Standardize on file_receive helper to move fds across processes On Thu, Jun 11, 2020 at 10:39:23AM +0000, Sargun Dhillon wrote: > On Thu, Jun 11, 2020 at 11:19:42AM +0200, Christian Brauner wrote: > > On Wed, Jun 10, 2020 at 07:59:55PM -0700, Kees Cook wrote: > > > On Wed, Jun 10, 2020 at 08:12:38AM +0000, Sargun Dhillon wrote: > > > > As an aside, all of this junk should be dropped: > > > > + ret = get_user(size, &uaddfd->size); > > > > + if (ret) > > > > + return ret; > > > > + > > > > + ret = copy_struct_from_user(&addfd, sizeof(addfd), uaddfd, size); > > > > + if (ret) > > > > + return ret; > > > > > > > > and the size member of the seccomp_notif_addfd struct. I brought this up > > > > off-list with Tycho that ioctls have the size of the struct embedded in them. We > > > > should just use that. The ioctl definition is based on this[2]: > > > > #define _IOC(dir,type,nr,size) \ > > > > (((dir) << _IOC_DIRSHIFT) | \ > > > > ((type) << _IOC_TYPESHIFT) | \ > > > > ((nr) << _IOC_NRSHIFT) | \ > > > > ((size) << _IOC_SIZESHIFT)) > > > > > > > > > > > > We should just use copy_from_user for now. In the future, we can either > > > > introduce new ioctl names for new structs, or extract the size dynamically from > > > > the ioctl (and mask it out on the switch statement in seccomp_notify_ioctl. > > > > > > Yeah, that seems reasonable. Here's the diff for that part: > > > > > > diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h > > > index 7b6028b399d8..98bf19b4e086 100644 > > > --- a/include/uapi/linux/seccomp.h > > > +++ b/include/uapi/linux/seccomp.h > > > @@ -118,7 +118,6 @@ struct seccomp_notif_resp { > > > > > > /** > > > * struct seccomp_notif_addfd > > > - * @size: The size of the seccomp_notif_addfd datastructure > > > * @id: The ID of the seccomp notification > > > * @flags: SECCOMP_ADDFD_FLAG_* > > > * @srcfd: The local fd number > > > @@ -126,7 +125,6 @@ struct seccomp_notif_resp { > > > * @newfd_flags: The O_* flags the remote FD should have applied > > > */ > > > struct seccomp_notif_addfd { > > > - __u64 size; > > > __u64 id; > > > __u32 flags; > > > __u32 srcfd; > > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > > > index 3c913f3b8451..00cbdad6c480 100644 > > > --- a/kernel/seccomp.c > > > +++ b/kernel/seccomp.c > > > @@ -1297,14 +1297,9 @@ static long seccomp_notify_addfd(struct seccomp_filter *filter, > > > struct seccomp_notif_addfd addfd; > > > struct seccomp_knotif *knotif; > > > struct seccomp_kaddfd kaddfd; > > > - u64 size; > > > int ret; > > > > > > - ret = get_user(size, &uaddfd->size); > > > - if (ret) > > > - return ret; > > > - > > > - ret = copy_struct_from_user(&addfd, sizeof(addfd), uaddfd, size); > > > + ret = copy_from_user(&addfd, uaddfd, sizeof(addfd)); > > > if (ret) > > > return ret; > > > > > > > > > > > > > > ---- > > > > +#define SECCOMP_IOCTL_NOTIF_ADDFD SECCOMP_IOR(3, \ > > > > + struct seccomp_notif_addfd) > > > > > > > > Lastly, what I believe to be a small mistake, it should be SECCOMP_IOW, based on > > > > the documentation in ioctl.h -- "_IOW means userland is writing and kernel is > > > > reading." > > > > > > Oooooh. Yeah; good catch. Uhm, that means SECCOMP_IOCTL_NOTIF_ID_VALID > > > is wrong too, yes? Tycho, Christian, how disruptive would this be to > > > fix? (Perhaps support both and deprecate the IOR version at some point > > > in the future?) > > > > We have custom defines in our source code, i.e. > > #define SECCOMP_IOCTL_NOTIF_ID_VALID SECCOMP_IOR(2, __u64) > > so ideally we'd have a SECCOMP_IOCTL_NOTIF_ID_VALID_V2 > > > > Does that sound ok? > > > > Christian > Why not change the public API in seccomp.h to: > #define SECCOMP_IOCTL_NOTIF_ID_VALID SECCOMP_IOW(2, __u64) > > And then in seccomp.c: > #define SECCOMP_IOCTL_NOTIF_ID_VALID_OLD SECCOMP_IOR(2, __u64) > static long seccomp_notify_ioctl(struct file *file, unsigned int cmd, > unsigned long arg) > { > struct seccomp_filter *filter = file->private_data; > void __user *buf = (void __user *)arg; > > switch (cmd) { > case SECCOMP_IOCTL_NOTIF_RECV: > return seccomp_notify_recv(filter, buf); > case SECCOMP_IOCTL_NOTIF_SEND: > return seccomp_notify_send(filter, buf); > case SECCOMP_IOCTL_NOTIF_ID_VALID_OLD: > pr_warn_once("Detected usage of legacy (incorrect) version of seccomp notifier notif_id_valid ioctl\n"); > case SECCOMP_IOCTL_NOTIF_ID_VALID: > return seccomp_notify_id_valid(filter, buf); > default: > return -EINVAL; > } > } > ---- > > So, both will work fine, and whenevery anyone recompiles, or picks up new > headers, they will start calling the "right" one without a code change, and > we wont break any userspace. Yeah, that's what I'd prefer here. -- Kees Cook
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