On Tue, Aug 11, 2020 at 7:43 PM Aleksa Sarai <cyphar@xxxxxxxxxx> wrote: > On 2020-08-11, Ross Zwisler <zwisler@xxxxxxxxxxxx> wrote: > > From: Mattias Nissler <mnissler@xxxxxxxxxxxx> > > > > For mounts that have the new "nosymfollow" option, don't follow symlinks > > when resolving paths. The new option is similar in spirit to the > > existing "nodev", "noexec", and "nosuid" options, as well as to the > > LOOKUP_NO_SYMLINKS resolve flag in the openat2(2) syscall. Various BSD > > variants have been supporting the "nosymfollow" mount option for a long > > time with equivalent implementations. > > > > Note that symlinks may still be created on file systems mounted with > > the "nosymfollow" option present. readlink() remains functional, so > > user space code that is aware of symlinks can still choose to follow > > them explicitly. > > > > Setting the "nosymfollow" mount option helps prevent privileged > > writers from modifying files unintentionally in case there is an > > unexpected link along the accessed path. The "nosymfollow" option is > > thus useful as a defensive measure for systems that need to deal with > > untrusted file systems in privileged contexts. > > > > More information on the history and motivation for this patch can be > > found here: > > > > https://sites.google.com/a/chromium.org/dev/chromium-os/chromiumos-design-docs/hardening-against-malicious-stateful-data#TOC-Restricting-symlink-traversal > > Looks good. Did you plan to add an in-tree test for this (you could > shove it in tools/testing/selftests/mount)? Sure, that sounds like a good idea. I'll take a look. > Reviewed-by: Aleksa Sarai <cyphar@xxxxxxxxxx> Thank you for the review.
