On Thu, Jun 4, 2020 at 5:57 PM Kees Cook <keescook@xxxxxxxxxxxx> wrote: > > On Thu, Jun 04, 2020 at 10:42:45AM +0200, glider@xxxxxxxxxx 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@xxxxxxxxxx> > > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > > Cc: Roy Yang <royyang@xxxxxxxxxx> > > Cc: <stable@xxxxxxxxxxxxxxx> # 4.1 > > Please include a Fixes (more below) and Link tags for details to help > guide backporting, then you don't need to bother with with "# 4.1", > the -stable tools will figure it out with a "Fixes" tag. > > Thanks for the v2! > > Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405 > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > > > 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. > > It seems like it came from this, but that's v4.5: > > Fixes: e4ad29fa0d22 ("ovl: use a minimal buffer in ovl_copy_xattr") I believe it's actually: Fixes: 0956254a2d5b ("ovl: don't copy up opaqueness") That patch added the ovl_is_private_xattr() check in ovl_copy_xattr(), without which 'error' was always initilalized. Thanks, Miklos
