userfaultfd: convert userfaultfd_ctx::refcount to refcount_t (ca880420) · Commits · 戴 / test

Reference counters should use refcount_t rather than atomic_t, since the refcount_t implementation can prevent overflows, reducing the exploitability of reference leak bugs. userfaultfd_ctx::refcount is a reference counter with the usual semantics, so convert it to refcount_t. Note: I replaced the BUG() on incrementing a 0 refcount with just refcount_inc(), since part of the semantics of refcount_t is that that incrementing a 0 refcount is not allowed; with CONFIG_REFCOUNT_FULL, refcount_inc() already checks for it and warns. Link: http://lkml.kernel.org/r/20181115003916.63381-1-ebiggers@kernel.org Signed-off-by:

Eric Biggers <ebiggers@google.com> Reviewed-by:

Andrew Morton <akpm@linux-foundation.org> Cc: Andrea Arcangeli <aarcange@redhat.com> Reviewed-by:

Mike Rapoport <rppt@linux.ibm.com> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

fs/userfaultfd.c

+5 −6

Original line number	Diff line number	Diff line
		@@ -53,7 +53,7 @@ struct userfaultfd_ctx {
		/* a refile sequence protected by fault_pending_wqh lock */
		struct seqcount refile_seq;
		/* pseudo fd refcounting */
		atomic_t refcount;
		refcount_t refcount;
		/* userfaultfd syscall flags */
		unsigned int flags;
		/* features requested from the userspace */
		@@ -140,8 +140,7 @@ out:
		*/
		static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
		{
		if (!atomic_inc_not_zero(&ctx->refcount))
		BUG();
		refcount_inc(&ctx->refcount);
		}

		/**
		@@ -154,7 +153,7 @@ static void userfaultfd_ctx_get(struct userfaultfd_ctx *ctx)
		*/
		static void userfaultfd_ctx_put(struct userfaultfd_ctx *ctx)
		{
		if (atomic_dec_and_test(&ctx->refcount)) {
		if (refcount_dec_and_test(&ctx->refcount)) {
		VM_BUG_ON(spin_is_locked(&ctx->fault_pending_wqh.lock));
		VM_BUG_ON(waitqueue_active(&ctx->fault_pending_wqh));
		VM_BUG_ON(spin_is_locked(&ctx->fault_wqh.lock));
		@@ -686,7 +685,7 @@ int dup_userfaultfd(struct vm_area_struct vma, struct list_head fcs)
		return -ENOMEM;
		}

		atomic_set(&ctx->refcount, 1);
		refcount_set(&ctx->refcount, 1);
		ctx->flags = octx->flags;
		ctx->state = UFFD_STATE_RUNNING;
		ctx->features = octx->features;
		@@ -1927,7 +1926,7 @@ SYSCALL_DEFINE1(userfaultfd, int, flags)
		if (!ctx)
		return -ENOMEM;

		atomic_set(&ctx->refcount, 1);
		refcount_set(&ctx->refcount, 1);
		ctx->flags = flags;
		ctx->features = 0;
		ctx->state = UFFD_STATE_WAIT_API;

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