ovl: initialize error in ovl_copy_xattr

In ovl_copy_xattr, if all the xattrs to be copied are overlayfs private
xattrs, the copy loop will terminate without assigning anything to the
error variable, thus returning an uninitialized value.

If ovl_copy_xattr is called from ovl_clear_empty, this uninitialized error
value is put into a pointer by ERR_PTR(), causing potential invalid memory
accesses down the line.

This commit initialize error with 0. This is the correct value because when
there's no xattr to copy, because all xattrs are private, ovl_copy_xattr
should succeed.

This bug is discovered with the help of INIT_STACK_ALL and clang.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1050405
Fixes: 0956254a2d5b ("ovl: don't copy up opaqueness")
Cc: stable@vger.kernel.org # v4.8
Signed-off-by: Alexander Potapenko <glider@google.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 66004534bd40c81e9a48a0eab9accc5f03de84e0..79dd052c7dbf5aae2aea21f883f1d26965c084ce 100644 (file)
--- 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) ||