From: Kees Cook <keescook@xxxxxxxxxxxx> Subject: mm/secretmem: avoid letting secretmem_users drop to zero 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 misuse 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 misuse 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(). Link: https://lkml.kernel.org/r/20211021154046.880251-1-keescook@xxxxxxxxxxxx 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> Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> Reviewed-by: Jordy Zomer <jordy@pwning.systems> Cc: Mike Rapoport <rppt@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/secretmem.c~mm-secretmem-avoid-letting-secretmem_users-drop-to-zero +++ a/mm/secretmem.c @@ -218,8 +218,8 @@ SYSCALL_DEFINE1(memfd_secret, unsigned i file->f_flags |= O_LARGEFILE; - fd_install(fd, file); atomic_inc(&secretmem_users); + fd_install(fd, file); return fd; err_put_fd: _
