Quoting Dmitry: "refcount_inc() needs to be done before fd_install(). After fd_install() finishes, the fd can be used by userspace and we can have secret data in memory before the refcount_inc(). A straightforward mis-use where a user will predict the returned fd in another thread before the syscall returns and will use it to store secret data is somewhat dubious because such a user just shoots themself in the foot. But a more interesting mis-use would be to close the predicted fd and decrement the refcount before the corresponding refcount_inc, this way one can briefly drop the refcount to zero while there are other users of secretmem." Move fd_install() after refcount_inc(). Cc: Mike Rapoport <rppt@xxxxxxxxxx> Cc: Jordy Zomer <jordy@pwning.systems> Cc: linux-mm@xxxxxxxxx Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Link: https://lore.kernel.org/lkml/CACT4Y+b1sW6-Hkn8HQYw_SsT7X3tp-CJNh2ci0wG3ZnQz9jjig@xxxxxxxxxxxxxx Fixes: 9a436f8ff631 ("PM: hibernate: disable when there are active secretmem users") Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/secretmem.c b/mm/secretmem.c index 1fea68b8d5a6..924d84ba481f 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -217,8 +217,8 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags) file->f_flags |= O_LARGEFILE; - fd_install(fd, file); refcount_inc(&secretmem_users); + fd_install(fd, file); return fd; err_put_fd: -- 2.30.2
