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Commit 46d0b24c authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Linus Torvalds
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userfaultfd_release: always remove uffd flags and clear vm_userfaultfd_ctx 

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: 04f5866e ("coredump: fix race condition between mmget_not_zero()/get_task_mm() and core dumping")
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Reported-by: default avatarKefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: default avatarAndrea Arcangeli <aarcange@redhat.com>
Tested-by: default avatarKefeng 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 7b2b55da

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: