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Thu, 14 Nov 2019 06:12:14 -0800 (PST) MIME-Version: 1.0 References: <20191107104957.306383-1-colin.king@canonical.com> In-Reply-To: From: Miklos Szeredi Date: Thu, 14 Nov 2019 15:12:04 +0100 Message-ID: Subject: Re: [PATCH][V2] ovl: fix lookup failure on multi lower squashfs To: Amir Goldstein Cc: Colin King , Miklos Szeredi , overlayfs , stable , kernel-janitors@vger.kernel.org, linux-kernel 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 Wed, Nov 13, 2019 at 5:34 PM Amir Goldstein wrote: > > On Wed, Nov 13, 2019 at 6:02 PM Miklos Szeredi wrote: > > > > 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; > > > - > > Colin, I mislead you, this should be (I think): > > if (!ofs->config.nfs_export && !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? > > It is bogus - it was my (wrong) suggestion. > The thinking was that we only decode origin fh if we have an upper layer > and index only valid with upper layer. > I forgot the case of nfs_export and lower-only setup. > Suggested fix above. > > > > > > + 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). > > > > Again, this was my (not wrong?) suggestion. > What this patch changes is that ovl_lower_uuid_ok() can now return false > and we get to this print although user did not ask for index nor nfs_export. > So the "falling back" language no longer makes sense. But does "enforcing" makes sense in this light? That's not what the detected bad_uuid condition is about, it's about failing to utilize origin markings to make inode numbers persistent for filesystems that have null uuid. Is that correct? Can we do a message that makes that somewhat more clearer? Thanks, Miklos