The patch titled Subject: mm/secretmem: avoid letting secretmem_users drop to zero has been added to the -mm tree. Its filename is mm-secretmem-avoid-letting-secretmem_users-drop-to-zero.patch

This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-secretmem-avoid-letting-secretm... and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-secretmem-avoid-letting-secretm...

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------------------------------------------------------ From: Kees Cook keescook@chromium.org 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@chromium.org Link: https://lore.kernel.org/lkml/CACT4Y+b1sW6-Hkn8HQYw_SsT7X3tp-CJNh2ci0wG3ZnQz9... Fixes: 9a436f8ff631 ("PM: hibernate: disable when there are active secretmem users") Signed-off-by: Kees Cook keescook@chromium.org Reported-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: Dmitry Vyukov dvyukov@google.com Reviewed-by: David Hildenbrand david@redhat.com Reviewed-by: Jordy Zomer jordy@pwning.systems Cc: Mike Rapoport rppt@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

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 @@ -217,8 +217,8 @@ SYSCALL_DEFINE1(memfd_secret, unsigned i

file->f_flags |= O_LARGEFILE;

- fd_install(fd, file); refcount_inc(&secretmem_users); + fd_install(fd, file); return fd;

err_put_fd: _

Patches currently in -mm which might be from keescook@chromium.org are

mm-secretmem-avoid-letting-secretmem_users-drop-to-zero.patch kasan-test-bypass-__alloc_size-checks.patch rapidio-avoid-bogus-__alloc_size-warning.patch compiler-attributes-add-__alloc_size-for-better-bounds-checking.patch slab-clean-up-function-prototypes.patch slab-add-__alloc_size-attributes-for-better-bounds-checking.patch mm-kvmalloc-add-__alloc_size-attributes-for-better-bounds-checking.patch mm-vmalloc-add-__alloc_size-attributes-for-better-bounds-checking.patch mm-page_alloc-add-__alloc_size-attributes-for-better-bounds-checking.patch percpu-add-__alloc_size-attributes-for-better-bounds-checking.patch kasan-test-consolidate-workarounds-for-unwanted-__alloc_size-protection.patch maintainers-add-exec-binfmt-section-with-myself-and-eric.patch binfmt_elf-reintroduce-using-map_fixed_noreplace.patch