Forwarded: [PATCH] hugetlbfs: skip VMAs without locks in hugetlb_vmdelete_list

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Subject: [PATCH] hugetlbfs: skip VMAs without locks in hugetlb_vmdelete_list
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master

hugetlb_vmdelete_list() can call unmap_hugepage_range() on VMAs that
have no associated lock, causing assertion failures in huge_pmd_unshare().

The function hugetlb_vma_trylock_write() returns 1 (success) even when
a VMA has neither a shareable lock nor a private lock. This allows
processing to continue, but when unmap_hugepage_range() is called, it
eventually reaches huge_pmd_unshare() which calls hugetlb_vma_assert_locked()
to verify a lock is held. The assertion fails because no lock was actually
acquired.

This results in a kernel panic:

  WARNING: CPU: 1 PID: 6594 Comm: syz.0.28 Not tainted
  Call Trace:
   hugetlb_vma_assert_locked+0x1dd/0x250
   huge_pmd_unshare+0x2c8/0x540
   __unmap_hugepage_range+0x6e3/0x1aa0
   unmap_hugepage_range+0x32e/0x410
   hugetlb_vmdelete_list+0x189/0x1f0

Fix by skipping VMAs that have no lock before calling unmap_hugepage_range(),
as the unmap operation requires lock protection.

Reported-by: syzbot+f26d7c75c26ec19790e7@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=f26d7c75c26ec19790e7
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 fs/hugetlbfs/inode.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index 9e0625167517..d2ecd83848e5 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -487,7 +487,8 @@ hugetlb_vmdelete_list(struct rb_root_cached *root, pgoff_t start, pgoff_t end,
 
 		if (!hugetlb_vma_trylock_write(vma))
 			continue;
-
+		if (!__vma_shareable_lock(vma) && !__vma_private_lock(vma))
+			continue;
 		v_start = vma_offset_start(vma, start);
 		v_end = vma_offset_end(vma, end);
 
-- 
2.43.0