On Thu, Jun 4, 2020 at 10:43 AM glider@google.com wrote:
Under certain circumstances (we found this out running Docker on a Clang-built kernel with CONFIG_INIT_STACK_ALL) ovl_copy_xattr() may return uninitialized value of |error| from ovl_copy_xattr(). It is then returned by ovl_create() to lookup_open(), which casts it to an invalid dentry pointer, that can be further read or written by the lookup_open() callers.
The uninitialized value is returned when all the xattr on the file are ovl_is_private_xattr(), which is actually a successful case, therefore we initialize |error| with 0.
Signed-off-by: Alexander Potapenko glider@google.com Cc: Kees Cook keescook@chromium.org Cc: Roy Yang royyang@google.com Cc: stable@vger.kernel.org # 4.1
The bug seem to date back to at least v4.1 where the annotation has been introduced (i.e. the compilers started noticing error could be used before being initialized). I hovever didn't try to prove that the problem is actually reproducible on such ancient kernels. We've seen it on a real machine running v4.4 as well.
v2: -- Per Vivek Goyal's suggestion, changed |error| to be 0
Thanks, applied patch posted here (with your signed-off as well, since the patch is the same...):
https://lore.kernel.org/linux-unionfs/874ks212uj.fsf@m5Zedd9JOGzJrf0/
Miklos