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 --- fs/overlayfs/copy_up.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c index 9709cf22cab3..07e0d1961e96 100644 --- a/fs/overlayfs/copy_up.c +++ b/fs/overlayfs/copy_up.c @@ -47,7 +47,7 @@ int ovl_copy_xattr(struct dentry *old, struct dentry *new) { ssize_t list_size, size, value_size = 0; char *buf, *name, *value = NULL; - int uninitialized_var(error); + int error = 0; size_t slen;
if (!(old->d_inode->i_opflags & IOP_XATTR) ||