Commit cc30042d authored Nov 19, 2021 by Mina Almasry Committed by Linus Torvalds Nov 20, 2021

hugetlb, userfaultfd: fix reservation restore on userfaultfd error

Currently in the is_continue case in hugetlb_mcopy_atomic_pte(), if we
bail out using "goto out_release_unlock;" in the cases where idx >=
size, or !huge_pte_none(), the code will detect that new_pagecache_page
== false, and so call restore_reserve_on_error().  In this case I see
restore_reserve_on_error() delete the reservation, and the following
call to remove_inode_hugepages() will increment h->resv_hugepages
causing a 100% reproducible leak.

We should treat the is_continue case similar to adding a page into the
pagecache and set new_pagecache_page to true, to indicate that there is
no reservation to restore on the error path, and we need not call
restore_reserve_on_error().  Rename new_pagecache_page to
page_in_pagecache to make that clear.

Link: https://lkml.kernel.org/r/20211117193825.378528-1-almasrymina@google.com


Fixes: c7b1850d ("hugetlb: don't pass page cache pages to restore_reserve_on_error")
Signed-off-by: Mina Almasry <almasrymina@google.com>
Reported-by: James Houghton <jthoughton@google.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Wei Xu <weixugc@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent afe041c2

mm/hugetlb.c

+4 −3

Original line number	Diff line number	Diff line
		@@ -5736,13 +5736,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
		int ret = -ENOMEM;
		struct page *page;
		int writable;
		bool new_pagecache_page = false;
		bool page_in_pagecache = false;

		if (is_continue) {
		ret = -EFAULT;
		page = find_lock_page(mapping, idx);
		if (!page)
		goto out;
		page_in_pagecache = true;
		} else if (!*pagep) {
		/* If a page already exists, then it's UFFDIO_COPY for
		* a non-missing case. Return -EEXIST.
		@@ -5830,7 +5831,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
		ret = huge_add_to_page_cache(page, mapping, idx);
		if (ret)
		goto out_release_nounlock;
		new_pagecache_page = true;
		page_in_pagecache = true;
		}

		ptl = huge_pte_lockptr(h, dst_mm, dst_pte);
		@@ -5894,7 +5895,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_struct *dst_mm,
		if (vm_shared \|\| is_continue)
		unlock_page(page);
		out_release_nounlock:
		if (!new_pagecache_page)
		if (!page_in_pagecache)
		restore_reserve_on_error(h, dst_vma, dst_addr, page);
		put_page(page);
		goto out;