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Wed, 13 Nov 2019 08:02:20 -0800 (PST) MIME-Version: 1.0 References: <20191107104957.306383-1-colin.king@canonical.com> In-Reply-To: <20191107104957.306383-1-colin.king@canonical.com> From: Miklos Szeredi Date: Wed, 13 Nov 2019 17:02:10 +0100 Message-ID: Subject: Re: [PATCH][V2] ovl: fix lookup failure on multi lower squashfs To: Colin King Cc: Miklos Szeredi , Amir Goldstein , overlayfs , stable , kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: stable-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Thu, Nov 7, 2019 at 11:50 AM Colin King wrote: > > From: Colin Ian King > > 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 > 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 > Signed-off-by: Colin Ian King > --- > 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)) { This seems bogus: why only check conflicting lower layers if there's an upper layer? > + 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", And this while this makes sense, it doesn't really fit into this patch (no change of behavior regarding how index and nfs_export are handled). Thanks, Miklos