New subject: [PATCH 2/8] ovl: generalize the lower_layers[] array

24 Jun 2020

From: Amir Goldstein amir73il@gmail.com
mainline inclusion
from mainline-5.5-rc2
commit 7e63c87fc2dcf3be9d3aab82d4a0ea085880bdca
category: bugfix
bugzilla: 37632
CVE: NA
---------------------------
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.
There is an unhandled corner case described by Miklos this way:
- two filesystems, A and B, both have null uuid
- upper layer is on A
- lower layer 1 is also on A
- lower layer 2 is on B
In this case bad_uuid won't be set for B, because the check only
involves the list of lower fs.  Hence we'll try to decode a layer 2
origin on layer 1 and fail.
We will deal with this corner case later.
Reported-by: Colin Ian King colin.king@canonical.com
Tested-by: Colin Ian King colin.king@canonical.com
Link: https://lore.kernel.org/lkml/20191106234301.283006-1-colin.king@canonical.co...
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: Miklos Szeredi mszeredi@redhat.com
Signed-off-by: Zhihao Cheng chengzhihao1@huawei.com
Reviewed-by: zhangyi (F) yi.zhang@huawei.com
Signed-off-by: Yang Yingliang yangyingliang@huawei.com
---
 fs/overlayfs/namei.c     |  8 ++++++++
 fs/overlayfs/ovl_entry.h |  2 ++
 fs/overlayfs/super.c     | 24 +++++++++++++++++-------
 3 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
index badf039267a2..62515ec25481 100644
--- a/fs/overlayfs/namei.c
+++ b/fs/overlayfs/namei.c
@@ -328,6 +328,14 @@ 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 1a1adc697c55..787fe4be835e 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -25,6 +25,8 @@ 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 ddcf8d3a83bf..3881f07a2434 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -1259,7 +1259,7 @@ 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))
+	if (!ofs->config.nfs_export && !ofs->upper_mnt)
    	return true;
for (i = 0; i < ofs->numlowerfs; i++) {
@@ -1267,9 +1267,13 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
    	 * 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;
 }
@@ -1281,6 +1285,7 @@ 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)
@@ -1292,11 +1297,15 @@ static int ovl_get_fsid(struct ovl_fs *ofs, const struct path *path)
    }
if (!ovl_lower_uuid_ok(ofs, &sb->s_uuid)) {
-		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",
-			uuid_is_null(&sb->s_uuid) ? "null" : "conflicting",
-			path->dentry);
+		bad_uuid = true;
+		if (ofs->config.index || ofs->config.nfs_export) {
+			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",
+				uuid_is_null(&sb->s_uuid) ? "null" :
+							    "conflicting",
+				path->dentry);
+		}
    }
err = get_anon_bdev(&dev);
@@ -1307,6 +1316,7 @@ 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;
-- 
2.25.1

    

[PATCH 1/8] ovl: fix lookup failure on multi lower squashfs