Date: Thu, 30 Nov 2017 20:14:38 +0100 From: Solar Designer <solar@...nwall.com> To: Salvatore Mesoraca <s.mesoraca16@...il.com> Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com> Subject: Re: Re: [PATCH v3 0/2] Restrict dangerous open in sticky directories On Thu, Nov 30, 2017 at 08:05:39PM +0100, Solar Designer wrote: > A new thought: a directory that has someone else as its owner is for our > purposes effectively the same as a group-writable directory. So maybe > whatever we'll implement for group-writable directories should also be > done for directories that have other than the current fsuid as their > owner. It's currently very uncommon to have directories with the sticky > bit set that are not at least group-writable, so this will rarely make a > difference (and when it does, that's just right), but also it provides a > way to explicitly include any directory under this monitoring (if the > group-writable protection is on) - e.g., if a sysadmin wants this > monitoring for users' home directories, they can change permissions for > those from e.g. 700 to 1700. This could be handy for development and > auditing of software, even though in production it could be easily > circumvented by the directory owner (who can remove the sticky bit, > which we should document to avoid providing a false sense of security) > and it won't automatically apply to subdirectories. It'd also cover > part of what we intend to achieve later by possibly extending the > feature to non-sticky directories, where we might also want to treat > different owner the same as group-writable (without the circumvention). Of course, where I wrote "other than the current fsuid", it should be "a non-root user other than the current fsuid". We trust root. Alexander
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