On Thu, Jun 04, 2020 at 10:57:24AM +0200, Miklos Szeredi wrote: > On Thu, Jun 4, 2020 at 10:43 AM <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 > > > > --- > > > > 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/ Can you please add: Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405 Fixes: e4ad29fa0d22 ("ovl: use a minimal buffer in ovl_copy_xattr") Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> (and adjust the CC field to drop the "# 4.1" so tools can figure it out?) Thanks! -- Kees Cook
