linux-kernel - [PATCH] mm/hugetlb: Don't call region_abort if region

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Message-Id: <1490328162-21245-1-git-send-email-mike.kravetz@oracle.com>
Date:   Thu, 23 Mar 2017 21:02:42 -0700
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, Michal Hocko <mhocko@...e.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Andrew Morton <akpm@...ux^Coundation.org>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH] mm/hugetlb: Don't call region_abort if region_chg fails

Changes to hugetlbfs reservation maps is a two step process.  The first
step is a call to region_chg to determine what needs to be changed, and
prepare that change.  This should be followed by a call to call to
region_add to commit the change, or region_abort to abort the change.

The error path in hugetlb_reserve_pages called region_abort after a
failed call to region_chg.  As a result, the adds_in_progress counter
in the reservation map is off by 1.  This is caught by a VM_BUG_ON
in resv_map_release when the reservation map is freed.

syzkaller fuzzer found this bug, that resulted in the following:

 kernel BUG at mm/hugetlb.c:742!
 Call Trace:
  hugetlbfs_evict_inode+0x7b/0xa0 fs/hugetlbfs/inode.c:493
  evict+0x481/0x920 fs/inode.c:553
  iput_final fs/inode.c:1515 [inline]
  iput+0x62b/0xa20 fs/inode.c:1542
  hugetlb_file_setup+0x593/0x9f0 fs/hugetlbfs/inode.c:1306
  newseg+0x422/0xd30 ipc/shm.c:575
  ipcget_new ipc/util.c:285 [inline]
  ipcget+0x21e/0x580 ipc/util.c:639
  SYSC_shmget ipc/shm.c:673 [inline]
  SyS_shmget+0x158/0x230 ipc/shm.c:657
  entry_SYSCALL_64_fastpath+0x1f/0xc2
 RIP: resv_map_release+0x265/0x330 mm/hugetlb.c:742

Reported-by: Dmitry Vyukov <dvyukov@...gle.com>
Signed-off-by: Mike Kravetz <mike.kravetz@...cle.com>
---
 mm/hugetlb.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c7025c1..c65d45c 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4233,7 +4233,9 @@ int hugetlb_reserve_pages(struct inode *inode,
 	return 0;
 out_err:
 	if (!vma || vma->vm_flags & VM_MAYSHARE)
-		region_abort(resv_map, from, to);
+		/* Don't call region_abort if region_chg failed */
+		if (chg >= 0)
+			region_abort(resv_map, from, to);
 	if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
 		kref_put(&resv_map->refs, resv_map_release);
 	return ret;
-- 
2.7.4