On Thu, Jun 04, 2020 at 10:42:45AM +0200, gli...@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 <gli...@google.com> > Cc: Kees Cook <keesc...@chromium.org> > Cc: Roy Yang <royy...@google.com> > Cc: <sta...@vger.kernel.org> # 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 <keesc...@chromium.org> > 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") What did you find in v4.1? It looks like error isn't uninitialized in v4.1: int ovl_copy_xattr(struct dentry *old, struct dentry *new) { ssize_t list_size, size; char *buf, *name, *value; int error; if (!old->d_inode->i_op->getxattr || !new->d_inode->i_op->getxattr) return 0; list_size = vfs_listxattr(old, NULL, 0); if (list_size <= 0) { if (list_size == -EOPNOTSUPP) return 0; return list_size; } buf = kzalloc(list_size, GFP_KERNEL); if (!buf) return -ENOMEM; error = -ENOMEM; ... But v4.1.52 backported the above patch (e4ad29fa0d22), which is why I don't try to figure these things out manually. Once we find the commit, the tools will figure it out. I think you just need: Fixes: e4ad29fa0d22 ("ovl: use a minimal buffer in ovl_copy_xattr") Cc: sta...@vger.kernel.org and things like v4.1.52 will get fixed (if anyone is actually doing updates for v4.1.z any more...) -- Kees Cook
