4.9-stable review patch. If anyone has any objections, please let me know.
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From: Cong Wang xiyou.wangcong@gmail.com
commit 073c516ff73557a8f7315066856c04b50383ac34 upstream.
Andrey reported a use-after-free in __ns_get_path():
spin_lock include/linux/spinlock.h:299 [inline] lockref_get_not_dead+0x19/0x80 lib/lockref.c:179 __ns_get_path+0x197/0x860 fs/nsfs.c:66 open_related_ns+0xda/0x200 fs/nsfs.c:143 sock_ioctl+0x39d/0x440 net/socket.c:1001 vfs_ioctl fs/ioctl.c:45 [inline] do_vfs_ioctl+0x1bf/0x1780 fs/ioctl.c:685 SYSC_ioctl fs/ioctl.c:700 [inline] SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691
We are under rcu read lock protection at that point:
rcu_read_lock(); d = atomic_long_read(&ns->stashed); if (!d) goto slow; dentry = (struct dentry *)d; if (!lockref_get_not_dead(&dentry->d_lockref)) goto slow; rcu_read_unlock();
but don't use a proper RCU API on the free path, therefore a parallel __d_free() could free it at the same time. We need to mark the stashed dentry with DCACHE_RCUACCESS so that __d_free() will be called after all readers leave RCU.
Fixes: e149ed2b805f ("take the targets of /proc/*/ns/* symlinks to separate fs") Cc: Alexander Viro viro@zeniv.linux.org.uk Cc: Andrew Morton akpm@linux-foundation.org Reported-by: Andrey Konovalov andreyknvl@google.com Signed-off-by: Cong Wang xiyou.wangcong@gmail.com Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Cc: Eric Biggers ebiggers3@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/nsfs.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/nsfs.c +++ b/fs/nsfs.c @@ -90,6 +90,7 @@ slow: return ERR_PTR(-ENOMEM); } d_instantiate(dentry, inode); + dentry->d_flags |= DCACHE_RCUACCESS; dentry->d_fsdata = (void *)ns->ops; d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry); if (d) {