On Thu, Aug 27, 2020 at 09:08:01PM +0100, Al Viro wrote: > On Thu, Aug 27, 2020 at 11:09:46AM -0600, Ross Zwisler 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 > > > > Signed-off-by: Mattias Nissler <mnissler@xxxxxxxxxxxx> > > Signed-off-by: Ross Zwisler <zwisler@xxxxxxxxxx> > > Reviewed-by: Aleksa Sarai <cyphar@xxxxxxxxxx> > > --- > > Changes since v8 [1]: > > * Look for MNT_NOSYMFOLLOW in link->mnt->mnt_flags so we are testing > > the link itself rather than the directory holding the link. (Al Viro) > > * Rebased onto v5.9-rc2. > > AFAICS, it applies clean to -rc1; what was the rebase about? Applied (to -rc1) and pushed
