Re: [PATCH][V2] ovl: fix lookup failure on multi lower squashfs

[Colin Ian King <colin.king@canonical.com>]

Hi there,

I was wondering if this fix will get applied?

Colin

On 07/11/2019 10:49, Colin King wrote:
> From: Colin Ian King <colin.king@canonical.com>
> 
> In the past, overlayfs required that lower fs have non null uuid in
> order to support nfs export and decode copy up origin file handles.
> 
> Commit 9df085f3c9a2 ("ovl: relax requirement for non null uuid of
> lower fs") relaxed this requirement for nfs export support, as long
> as uuid (even if null) is unique among all lower fs.
> 
> However, said commit unintentionally also relaxed the non null uuid
> requirement for decoding copy up origin file handles, regardless of
> the unique uuid requirement.
> 
> Amend this mistake by disabling decoding of copy up origin file handle
> from lower fs with a conflicting uuid.
> 
> We still encode copy up origin file handles from those fs, because
> file handles like those already exist in the wild and because they
> might provide useful information in the future.
> 
> Reported-by: Colin Ian King <colin.king@canonical.com>
> Link: https://lore.kernel.org/lkml/20191106234301.283006-1-colin.king@canonical.com/
> Fixes: 9df085f3c9a2 ("ovl: relax requirement for non null uuid ...")
> Cc: stable@vger.kernel.org # v4.20+
> Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> Signed-off-by: Colin Ian King <colin.king@canonical.com>
> ---
>  fs/overlayfs/namei.c     |  8 ++++++++
>  fs/overlayfs/ovl_entry.h |  2 ++
>  fs/overlayfs/super.c     | 16 ++++++++++------
>  3 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index e9717c2f7d45..f47c591402d7 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -325,6 +325,14 @@ int ovl_check_origin_fh(struct ovl_fs *ofs, struct ovl_fh *fh, bool connected,
>  	int i;
>  
>  	for (i = 0; i < ofs->numlower; i++) {
> +		/*
> +		 * If lower fs uuid is not unique among lower fs we cannot match
> +		 * fh->uuid to layer.
> +		 */
> +		if (ofs->lower_layers[i].fsid &&
> +		    ofs->lower_layers[i].fs->bad_uuid)
> +			continue;
> +
>  		origin = ovl_decode_real_fh(fh, ofs->lower_layers[i].mnt,
>  					    connected);
>  		if (origin)
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index a8279280e88d..28348c44ea5b 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -22,6 +22,8 @@ struct ovl_config {
>  struct ovl_sb {
>  	struct super_block *sb;
>  	dev_t pseudo_dev;
> +	/* Unusable (conflicting) uuid */
> +	bool bad_uuid;
>  };
>  
>  struct ovl_layer {
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index afbcb116a7f1..5d4faab57ba0 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -1255,17 +1255,18 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
>  {
>  	unsigned int i;
>  
> -	if (!ofs->config.nfs_export && !(ofs->config.index && ofs->upper_mnt))
> -		return true;
> -
>  	for (i = 0; i < ofs->numlowerfs; i++) {
>  		/*
>  		 * We use uuid to associate an overlay lower file handle with a
>  		 * lower layer, so we can accept lower fs with null uuid as long
>  		 * as all lower layers with null uuid are on the same fs.
> +		 * if we detect multiple lower fs with the same uuid, we
> +		 * disable lower file handle decoding on all of them.
>  		 */
> -		if (uuid_equal(&ofs->lower_fs[i].sb->s_uuid, uuid))
> +		if (uuid_equal(&ofs->lower_fs[i].sb->s_uuid, uuid)) {
> +			ofs->lower_fs[i].bad_uuid = true;
>  			return false;
> +		}
>  	}
>  	return true;
>  }
> @@ -1277,6 +1278,7 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
>  	unsigned int i;
>  	dev_t dev;
>  	int err;
> +	bool bad_uuid = false;
>  
>  	/* fsid 0 is reserved for upper fs even with non upper overlay */
>  	if (ofs->upper_mnt && ofs->upper_mnt->mnt_sb == sb)
> @@ -1287,10 +1289,11 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
>  			return i + 1;
>  	}
>  
> -	if (!ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
> +	if (ofs->upper_mnt && !ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
> +		bad_uuid = true;
>  		ofs->config.index = false;
>  		ofs->config.nfs_export = false;
> -		pr_warn("overlayfs: %s uuid detected in lower fs '%pd2', falling back to index=off,nfs_export=off.\n",
> +		pr_warn("overlayfs: %s uuid detected in lower fs '%pd2', enforcing index=off,nfs_export=off.\n",
>  			uuid_is_null(&sb->s_uuid) ? "null" : "conflicting",
>  			path->dentry);
>  	}
> @@ -1303,6 +1306,7 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
>  
>  	ofs->lower_fs[ofs->numlowerfs].sb = sb;
>  	ofs->lower_fs[ofs->numlowerfs].pseudo_dev = dev;
> +	ofs->lower_fs[ofs->numlowerfs].bad_uuid = bad_uuid;
>  	ofs->numlowerfs++;
>  
>  	return ofs->numlowerfs;
>