[PATCH 1/9] vfs: fix infinite loop caused by clone_mnt race

[Miklos Szeredi]

From: Miklos Szeredi <mszeredi@xxxxxxx>

If clone_mnt() happens while mnt_make_readonly() is running, the
cloned mount might have MNT_WRITE_HOLD flag set, which results in
mnt_want_write() spinning forever on this mount.

Needs CAP_SYS_ADMIN to trigger deliberately and unlikely to happen
accidentally.  But if it does happen it can hang the machine.

Signed-off-by: Miklos Szeredi <mszeredi@xxxxxxx>
---
 fs/namespace.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-2.6/fs/namespace.c
===================================================================
--- linux-2.6.orig/fs/namespace.c	2010-10-01 21:54:17.000000000 +0200
+++ linux-2.6/fs/namespace.c	2010-10-01 21:54:30.000000000 +0200
@@ -595,7 +595,7 @@ static struct vfsmount *clone_mnt(struct
 				goto out_free;
 		}
 
-		mnt->mnt_flags = old->mnt_flags;
+		mnt->mnt_flags = old->mnt_flags & ~MNT_WRITE_HOLD;
 		atomic_inc(&sb->s_active);
 		mnt->mnt_sb = sb;
 		mnt->mnt_root = dget(root);

-- 
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