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Date:   Tue, 4 Jun 2019 11:46:11 -0400
To:     Trond Myklebust <trondmy@gmail.com>
Cc:     Steve Dickson <SteveD@redhat.com>,
        "J. Bruce Fields" <bfields@redhat.com>, linux-nfs@vger.kernel.org
Subject: Re: [PATCH 2/3] mountd: Ensure nfsd_path_strip_root() uses the
 canonicalised path
Message-ID: <20190604154611.GC19422@fieldses.org>
References: <20190603171227.29148-1-trond.myklebust@hammerspace.com>
 <20190603171227.29148-2-trond.myklebust@hammerspace.com>
 <20190603171227.29148-3-trond.myklebust@hammerspace.com>
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User-Agent: Mutt/1.5.21 (2010-09-15)
From:   bfields@fieldses.org (J. Bruce Fields)
Sender: linux-nfs-owner@vger.kernel.org
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On Mon, Jun 03, 2019 at 01:12:26PM -0400, Trond Myklebust wrote:
> When attempting to strip the root path, we should first canonicalise
> the root pathname.
> 
> Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>
> ---
>  support/misc/nfsd_path.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/support/misc/nfsd_path.c b/support/misc/nfsd_path.c
> index 2f41a793c534..9b38dd96007f 100644
> --- a/support/misc/nfsd_path.c
> +++ b/support/misc/nfsd_path.c
> @@ -1,6 +1,7 @@
>  #include <errno.h>
>  #include <sys/types.h>
>  #include <sys/stat.h>
> +#include <limits.h>
>  #include <stdlib.h>
>  #include <unistd.h>
>  
> @@ -62,13 +63,21 @@ nfsd_path_nfsd_rootdir(void)
>  char *
>  nfsd_path_strip_root(char *pathname)
>  {
> +	char buffer[PATH_MAX];
>  	const char *dir = nfsd_path_nfsd_rootdir();
>  	char *ret;
>  
> -	ret = strstr(pathname, dir);
> -	if (!ret || ret != pathname)
> -		return pathname;
> -	return pathname + strlen(dir);
> +	if (!dir)
> +		goto out;
> +	if (realpath(dir, buffer)) {
> +		ret = strstr(pathname, buffer);
> +		if (ret == pathname)
> +			return pathname + strlen(dir);
> +	} else
> +		xlog(D_GENERAL, "%s: failed to resolve path %s: %m",
> +				__func__, dir);
> +out:
> +	return pathname;

I still don't get this.

So in the case strstr doesn't find anything, it returns the path
unchanged.

That means that if the next_mnt() caller asks whether there are any
mounts underneath /rootdir/a/b, and nextdir finds a mountpoint at
/a/b/c, it can return that, right?

--b.


>  }
>  
>  char *
> -- 
> 2.21.0