linux-kernel - Re: [PATCH] cachefiles: Fix the volume coherency check

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Message-ID: <cc2a90295935c8841abf5d0538590eb5202a745c.camel@kernel.org>
Date:   Mon, 31 Jan 2022 13:43:18 -0500
From:   Jeff Layton <jlayton@...nel.org>
To:     David Howells <dhowells@...hat.com>, smfrench@...il.com
Cc:     linux-cifs@...r.kernel.org, linux-cachefs@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cachefiles: Fix the volume coherency check

On Mon, 2022-01-31 at 17:52 +0000, David Howells wrote:
> Fix the cache volume coherency attribute check.  It was copied from the
> file coherency check which uses as struct to lay out the xattr, and so
> needs to add a bit on to find the coherency data - but the volume coherency
> attribute only contains the coherency data, so we shouldn't be using the
> layout struct for it.
> 
> This has passed unnoticed so far because it only affects cifs at the
> moment, and cifs had its fscache component disabled.
> 
> This can now be checked by enabling CONFIG_CIFS_FSCACHE, enabling the
> following tracepoint:
> 
> 	/sys/kernel/debug/tracing/events/cachefiles/cachefiles_vol_coherency/enable
> 
> and making a cifs mount.  Without this change, the trace shows a
> cachefiles_vol_coherency line with "VOL BAD cmp" in it; with this change it
> shows "VOL OK" instead.
> 
> Fixes: 32e150037dce ("fscache, cachefiles: Store the volume coherency data")
> Signed-off-by: David Howells <dhowells@...hat.com>
> cc: Jeff Layton <jlayton@...nel.org>
> cc: Steve French <smfrench@...il.com>
> cc: linux-cifs@...r.kernel.org
> cc: linux-cachefs@...hat.com
> ---
> 
>  fs/cachefiles/xattr.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/cachefiles/xattr.c b/fs/cachefiles/xattr.c
> index 83f41bd0c3a9..c6171e818a7c 100644
> --- a/fs/cachefiles/xattr.c
> +++ b/fs/cachefiles/xattr.c
> @@ -218,10 +218,10 @@ bool cachefiles_set_volume_xattr(struct cachefiles_volume *volume)
>   */
>  int cachefiles_check_volume_xattr(struct cachefiles_volume *volume)
>  {
> -	struct cachefiles_xattr *buf;
>  	struct dentry *dentry = volume->dentry;
>  	unsigned int len = volume->vcookie->coherency_len;
>  	const void *p = volume->vcookie->coherency;
> +	void *buf;
>  	enum cachefiles_coherency_trace why;
>  	ssize_t xlen;
>  	int ret = -ESTALE;
> @@ -245,7 +245,7 @@ int cachefiles_check_volume_xattr(struct cachefiles_volume *volume)
>  					"Failed to read xattr with error %zd", xlen);
>  		}
>  		why = cachefiles_coherency_vol_check_xattr;
> -	} else if (memcmp(buf->data, p, len) != 0) {
> +	} else if (memcmp(buf, p, len) != 0) {
>  		why = cachefiles_coherency_vol_check_cmp;
>  	} else {
>  		why = cachefiles_coherency_vol_check_ok;
> 
> 

Reviewed-by: Jeff Layton <jlayton@...nel.org>