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?
