linux-kernel - [PATCH 5.15 197/279] hugetlb, userfaultfd: fix reservation restore on userfaultfd error

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Message-Id: <20211124115725.541561611@linuxfoundation.org>
Date:   Wed, 24 Nov 2021 12:58:04 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Mina Almasry <almasrymina@...gle.com>,
        James Houghton <jthoughton@...gle.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Wei Xu <weixugc@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 5.15 197/279] hugetlb, userfaultfd: fix reservation restore on userfaultfd error

From: Mina Almasry <almasrymina@...gle.com>

commit cc30042df6fcc82ea18acf0dace831503e60a0b7 upstream.

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: c7b1850dfb41 ("hugetlb: don't pass page cache pages to restore_reserve_on_error")
Signed-off-by: Mina Almasry <almasrymina@...gle.com>
Reported-by: James Houghton <jthoughton@...gle.com>
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
Cc: Wei Xu <weixugc@...gle.com>
Cc: <stable@...r.kernel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 mm/hugetlb.c |    7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5236,13 +5236,14 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 	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.
@@ -5330,7 +5331,7 @@ int hugetlb_mcopy_atomic_pte(struct mm_s
 		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);
@@ -5394,7 +5395,7 @@ out_release_unlock:
 	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;