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From: "J. Bruce Fields" <>
To: Jesper Juhl <>
	Kendrick Smith <>,
	Andy Adamson <>,
	Trond Myklebust <>
Subject: Re: [PATCH] NFS4: Fix NULL deref in nfsd4_lock() by makeing unhash_lockowner() safe to call with NULL arg
Date: Mon, 30 Jan 2012 16:43:51 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Sun, Jan 29, 2012 at 10:29:24PM +0100, Jesper Juhl wrote:
> The Coverity checker noticed a path through nfsd4_lock() where we call
> release_lockowner(lock_sop); (at the 'out:' label) where 'lock_sop' is
> That goes bad since release_lockowner() calls unhash_lockowner() which
> dereferences its argument.
> release_lockowner() also calls nfs4_free_lockowner(), but that's not a
> problem since that function just calls kfree() and kmem_cache_free(),
> both of which are safe to call with NULL as argument.
> There are several ways to fix the bug.
>  - rework nfsd4_lock() so the call to release_lockowner(NULL) will never happen.
>  - let release_lockowner() test for NULL and return if given one.
>  - let unhash_lockowner() test for NULL and return if given one (which makes both it and release_lockowner() safe).
> I chose the last option for this patch.
> For information, the path Coverity spotted (in defect report 201504) is this:

> [...]
> 4098out:
> At conditional (12): "status" taking the true branch.
> At conditional (13): "new_state" taking the true branch.
> 4099        if (status && new_state)

new_state is initialized false, and referenced otherwise only once,
when a reference ot is is passed here:

> 4010                status = lookup_or_create_lock_state(cstate, open_stp, lock,
> 4011                                                        &lock_stp, &new_state);

so if new_state is true, then lookup_or_create_lock_state() set it to
true.  But it sets that only in one spot, at the end:

	*new = true;
	return nfs_ok;

Note nfs_ok is zero.  Therefore:

> At conditional (11): "status" taking the true branch.
> 4012                if (status)
> 4013                        goto out;

this could not have happened.

So it looks like a Coverity bug.


  reply	other threads:[~2012-01-30 21:43 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-01-29 21:29 [PATCH] NFS4: Fix NULL deref in nfsd4_lock() by makeing unhash_lockowner() safe to call with NULL arg Jesper Juhl
2012-01-30 21:43 ` J. Bruce Fields [this message]
2012-07-22 21:01   ` Jesper Juhl

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