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| author | Kees Cook <keescook@chromium.org> | 2021-10-29 00:36:21 +0300 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2021-10-29 03:18:55 +0300 |
| commit | 855d44434fa24d5344c1cb0edb38723f891cd415 (patch) | |
| tree | c4550d2d91c2e494d21b37304c72dba65b4c0fa4 | |
| parent | 6f1b228529ae49b0f85ab89bcdb6c365df401558 (diff) | |
| download | linux-855d44434fa24d5344c1cb0edb38723f891cd415.tar.xz | |
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-CJNh2ci0wG3ZnQz9jjig@mail.gmail.com
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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
| -rw-r--r-- | mm/secretmem.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/mm/secretmem.c b/mm/secretmem.c index c2dda408bb36..22b310adb53d 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -218,8 +218,8 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags) file->f_flags |= O_LARGEFILE; - fd_install(fd, file); atomic_inc(&secretmem_users); + fd_install(fd, file); return fd; err_put_fd: |