Messages in this thread | | | Subject | Re: [PATCH] ksys_mount: check for permissions before resource allocation | From | Ilya Matveychikov <> | Date | Wed, 6 Jun 2018 13:32:12 +0400 |
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> On Jun 5, 2018, at 11:56 PM, Eric W. Biederman <ebiederm@xmission.com> wrote: > > Ilya Matveychikov <matvejchikov@gmail.com> writes: > >> Just CC’ed to some of maintainers. >> >> $ perl scripts/get_maintainer.pl fs/0001-ksys_mount-check-for-permissions-before-resource-all.patch >> Alexander Viro <viro@zeniv.linux.org.uk> (maintainer:FILESYSTEMS (VFS and infrastructure)) >> linux-fsdevel@vger.kernel.org (open list:FILESYSTEMS (VFS and infrastructure)) >> linux-kernel@vger.kernel.org (open list) >> >>> On Jun 5, 2018, at 6:00 AM, Ilya Matveychikov <matvejchikov@gmail.com> wrote: >>> >>> Early check for mount permissions prevents possible allocation of 3 >>> pages from kmalloc() pool by unpriveledged user which can be used for >>> spraying the kernel heap. > > *Snort* > > You clearly have not read may_mount. Your modified code still > let's unprivileged users in. So even if all of Al's good objections > were not applicable this change would still be buggy and wrong. > > Nacked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Don’t get me wrong but may_mount() is:
static inline bool may_mount(void) { return ns_capable(current->nsproxy->mnt_ns->user_ns, CAP_SYS_ADMIN); }
What do you mean by "You clearly have not read may_mount”? The only thing that can affect may_mount result (as mentioned earlier) is that task’s NS capability might be changed by security_sb_mount() hook.
So, do you think that is’s possible to NOT have CAP_SYS_ADMIN while entering to ksys_mount() but getting it with the security_sb_mount() hook?
This is the only case I see that using may_mount() before security_sb_mount() is wrong. This was the point?
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