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authorKees Cook <keescook@chromium.org>2021-10-28 14:36:21 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-10-28 17:18:55 -0700
commit855d44434fa24d5344c1cb0edb38723f891cd415 (patch)
treec4550d2d91c2e494d21b37304c72dba65b4c0fa4 /mm/secretmem.c
parent6f1b228529ae49b0f85ab89bcdb6c365df401558 (diff)
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>
Diffstat (limited to 'mm/secretmem.c')
-rw-r--r--mm/secretmem.c2
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: