userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx (46d0b24c) · Commits · 戴 / test

userfaultfd_release() should clear vm_flags/vm_userfaultfd_ctx even if mm->core_state != NULL. Otherwise a page fault can see userfaultfd_missing() == T and use an already freed userfaultfd_ctx. Link: http://lkml.kernel.org/r/20190820160237.GB4983@redhat.com Fixes: ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping") Signed-off-by:

Oleg Nesterov <oleg@redhat.com> Reported-by:

Kefeng Wang <wangkefeng.wang@huawei.com> Reviewed-by:

Andrea Arcangeli <aarcange@redhat.com> Tested-by:

Kefeng Wang <wangkefeng.wang@huawei.com> Cc: Peter Xu <peterx@redhat.com> Cc: Mike Rapoport <rppt@linux.ibm.com> Cc: Jann Horn <jannh@google.com> Cc: Jason Gunthorpe <jgg@mellanox.com> Cc: Michal Hocko <mhocko@suse.com> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> Cc: <stable@vger.kernel.org> Signed-off-by:

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

Linus Torvalds <torvalds@linux-foundation.org>

fs/userfaultfd.c

+13 −12

Original line number	Diff line number	Diff line
		@@ -880,6 +880,7 @@ static int userfaultfd_release(struct inode inode, struct file file)
		/* len == 0 means wake all */
		struct userfaultfd_wake_range range = { .len = 0, };
		unsigned long new_flags;
		bool still_valid;

		WRITE_ONCE(ctx->released, true);

		@@ -895,8 +896,7 @@ static int userfaultfd_release(struct inode inode, struct file file)
		* taking the mmap_sem for writing.
		*/
		down_write(&mm->mmap_sem);
		if (!mmget_still_valid(mm))
		goto skip_mm;
		still_valid = mmget_still_valid(mm);
		prev = NULL;
		for (vma = mm->mmap; vma; vma = vma->vm_next) {
		cond_resched();
		@@ -907,6 +907,7 @@ static int userfaultfd_release(struct inode inode, struct file file)
		continue;
		}
		new_flags = vma->vm_flags & ~(VM_UFFD_MISSING \| VM_UFFD_WP);
		if (still_valid) {
		prev = vma_merge(mm, prev, vma->vm_start, vma->vm_end,
		new_flags, vma->anon_vma,
		vma->vm_file, vma->vm_pgoff,
		@@ -916,10 +917,10 @@ static int userfaultfd_release(struct inode inode, struct file file)
		vma = prev;
		else
		prev = vma;
		}
		vma->vm_flags = new_flags;
		vma->vm_userfaultfd_ctx = NULL_VM_UFFD_CTX;
		}
		skip_mm:
		up_write(&mm->mmap_sem);
		mmput(mm);
		wakeup:

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