Commit 29fe8399 authored May 11, 2020 by J. Bruce Fields Committed by Trond Myklebust May 11, 2020

nfs: fix NULL deference in nfs4_get_valid_delegation



We add the new state to the nfsi->open_states list, making it
potentially visible to other threads, before we've finished initializing
it.

That wasn't a problem when all the readers were also taking the i_lock
(as we do here), but since we switched to RCU, there's now a possibility
that a reader could see the partially initialized state.

Symptoms observed were a crash when another thread called
nfs4_get_valid_delegation() on a NULL inode, resulting in an oops like:

	BUG: unable to handle page fault for address: ffffffffffffffb0 ...
	RIP: 0010:nfs4_get_valid_delegation+0x6/0x30 [nfsv4] ...
	Call Trace:
	 nfs4_open_prepare+0x80/0x1c0 [nfsv4]
	 __rpc_execute+0x75/0x390 [sunrpc]
	 ? finish_task_switch+0x75/0x260
	 rpc_async_schedule+0x29/0x40 [sunrpc]
	 process_one_work+0x1ad/0x370
	 worker_thread+0x30/0x390
	 ? create_worker+0x1a0/0x1a0
	 kthread+0x10c/0x130
	 ? kthread_park+0x80/0x80
	 ret_from_fork+0x22/0x30

Fixes: 9ae075fd "NFSv4: Convert open state lookup to use RCU"
Reviewed-by: Seiichi Ikarashi <s.ikarashi@fujitsu.com>
Tested-by: Daisuke Matsuda <matsuda-daisuke@fujitsu.com>
Tested-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Cc: stable@vger.kernel.org # v4.20+
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

parent 31e9a7f3

fs/nfs/nfs4state.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -734,9 +734,9 @@ nfs4_get_open_state(struct inode inode, struct nfs4_state_owner owner)
		state = new;
		state->owner = owner;
		atomic_inc(&owner->so_count);
		list_add_rcu(&state->inode_states, &nfsi->open_states);
		ihold(inode);
		state->inode = inode;
		list_add_rcu(&state->inode_states, &nfsi->open_states);
		spin_unlock(&inode->i_lock);
		/* Note: The reclaim code dictates that we add stateless
		* and read-only stateids to the end of the list */

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