linux-kernel - Re: [PATCH 1/1] nfsd: incorrect check for debugfs returns

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Date:	Wed, 25 Mar 2015 16:09:53 -0400
From:	"J. Bruce Fields" <bfields@...ldses.org>
To:	Chengyu Song <csong84@...ech.edu>
Cc:	linux-nfs@...r.kernel.org, linux-kernel@...r.kernel.org,
	Taesoo Kim <taesoo@...ech.edu>, changwoo@...ech.edu,
	sanidhya@...ech.edu, Byoungyoung Lee <blee@...ech.edu>
Subject: Re: [PATCH 1/1] nfsd: incorrect check for debugfs returns

On Wed, Mar 25, 2015 at 12:41:29PM -0400, Chengyu Song wrote:
> There may be a simpler solution, declare NFSD_FAULT_INJECTION has dependency
> on DEBUG_FS, or automatically select DEBUG_FS.

Oh, I forgot about that--you're right, NFSD_FAULT_INJECTION isn't useful
without DEBUG_FS anyway, so, sure, let's do that.

--b.

> I don't think current debugfs
> implementation will return any error ptr once it's configured.
> 
> I choose to check the return instead, because I was worried the debugfs interface
> may change in the future.
> 
> Does this sounds like a solution? If so, I can submit a patch for Kconfig.
> 
> Best,
> Chengyu
> 
> > On Mar 25, 2015, at 11:17 AM, J. Bruce Fields <bfields@...ldses.org> wrote:
> > 
> > On Mon, Mar 23, 2015 at 10:58:05PM -0400, Chengyu Song wrote:
> >> debugfs_create_dir and debugfs_create_file may return -ENODEV when debugfs
> >> is not configured, so the return value should be checked against ERROR_VALUE
> >> as well, otherwise the later dereference of the dentry pointer would crash
> >> the kernel.
> > 
> > Thanks for spotting this.  But it looks like this will cause nfsd
> > startup to fail when debugfs isn't configured.  I'd rather we didn't, it
> > just isn't that important.
> > 
> > So I'd rather just make nfsd_fault_inject_init() a void return--just do
> > a dprintk as a warning in the "fail" case, and otherwise let normal
> > startup continue (and check that doesn't lead to other unsafe
> > dereferences of debug_dir).  Could you try that?
> > 
> > --b.
> > 
> > 
> >> 
> >> Signed-off-by: Chengyu Song <csong84@...ech.edu>
> >> ---
> >> fs/nfsd/fault_inject.c | 12 ++++++++----
> >> 1 file changed, 8 insertions(+), 4 deletions(-)
> >> 
> >> diff --git a/fs/nfsd/fault_inject.c b/fs/nfsd/fault_inject.c
> >> index c16bf5a..621d065 100644
> >> --- a/fs/nfsd/fault_inject.c
> >> +++ b/fs/nfsd/fault_inject.c
> >> @@ -132,19 +132,23 @@ int nfsd_fault_inject_init(void)
> >> 	unsigned int i;
> >> 	struct nfsd_fault_inject_op *op;
> >> 	umode_t mode = S_IFREG | S_IRUSR | S_IWUSR;
> >> +	struct dentry *dent;
> >> 
> >> -	debug_dir = debugfs_create_dir("nfsd", NULL);
> >> -	if (!debug_dir)
> >> +	dent = debugfs_create_dir("nfsd", NULL);
> >> +	if (IS_ERR_OR_NULL(dent))
> >> 		goto fail;
> >> +	debug_dir = dent;
> >> 
> >> 	for (i = 0; i < NUM_INJECT_OPS; i++) {
> >> 		op = &inject_ops[i];
> >> -		if (!debugfs_create_file(op->file, mode, debug_dir, op, &fops_nfsd))
> >> +		dent = debugfs_create_file(op->file, mode, debug_dir, op, &fops_nfsd);
> >> +		if (IS_ERR_OR_NULL(dent))
> >> 			goto fail;
> >> +
> >> 	}
> >> 	return 0;
> >> 
> >> fail:
> >> 	nfsd_fault_inject_cleanup();
> >> -	return -ENOMEM;
> >> +	return dent ? PTR_ERR(dent) : -ENOMEM;
> >> }
> >> -- 
> >> 2.1.0
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