secretmem: Prevent secretmem_users from wrapping to zero

Commit 110860541f ("mm/secretmem: use refcount_t instead of atomic_t")
attempted to fix the problem of secretmem_users wrapping to zero and
allowing suspend once again.

But it was reverted in commit 87066fdd2e ("Revert 'mm/secretmem: use
refcount_t instead of atomic_t'") because of the problems it caused - a
refcount_t was not semantically the right type to use.

Instead prevent secretmem_users from wrapping to zero by forbidding new
users if the number of users has wrapped from positive to negative.
This stops a long way short of reaching the necessary 4 billion users
where it wraps to zero again, so there's no need to be clever with
special anti-wrap types or checking the return value from atomic_inc().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Jordy Zomer <jordy@pwning.systems>
Cc: Kees Cook <keescook@chromium.org>,
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

This commit is contained in:

Matthew Wilcox (Oracle)

2021-10-25 19:16:34 +01:00

committed by

Linus Torvalds

parent ac8a6eba2a

commit cb68543239

1 changed files with 2 additions and 0 deletions

									
										2

mm/secretmem.c

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				@ -203,6 +203,8 @@ SYSCALL_DEFINE1(memfd_secret, unsigned int, flags)

					if (flags & ~(SECRETMEM_FLAGS_MASK | O_CLOEXEC))

						return -EINVAL;

					if (atomic_read(&secretmem_users) < 0)

						return -ENFILE;

					fd = get_unused_fd_flags(flags & O_CLOEXEC);

					if (fd < 0)

secretmem: Prevent secretmem_users from wrapping to zero

2 mm/secretmem.c Unescape Escape View File

2

mm/secretmem.c

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