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ovl: fix corner case of conflicting lower layer uuid

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This fixes ovl_lower_uuid_ok() to correctly detect the corner case:
 - 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 would not have been set for B, because the check
only involved the list of lower fs.  Hence we'll try to decode a layer 2
origin on layer 1 and fail.

We check for conflicting (and null) uuid among all lower layers, including
those layers that are on the same fs as the upper layer.

Reported-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
This commit is contained in:
Amir Goldstein 2019-11-16 18:52:20 +02:00 committed by Miklos Szeredi
parent 07f1e59637
commit 1b81dddd35
2 changed files with 8 additions and 2 deletions
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2
fs/overlayfs/ovl_entry.h
View File

@ -24,6 +24,8 @@ struct ovl_sb {
dev_t pseudo_dev;
/* Unusable (conflicting) uuid */
bool bad_uuid;
/* Used as a lower layer (but maybe also as upper) */
bool is_lower;
};
struct ovl_layer {

8
fs/overlayfs/super.c
View File

@ -1260,7 +1260,7 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
if (!ofs->config.nfs_export && !ofs->upper_mnt)
return true;
for (i = 1; i < ofs->numfs; i++) {
for (i = 0; i < ofs->numfs; 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
@ -1268,7 +1268,8 @@ static bool ovl_lower_uuid_ok(struct ovl_fs *ofs, const uuid_t *uuid)
* if we detect multiple lower fs with the same uuid, we
* disable lower file handle decoding on all of them.
*/
if (uuid_equal(&ofs->fs[i].sb->s_uuid, uuid)) {
if (ofs->fs[i].is_lower &&
uuid_equal(&ofs->fs[i].sb->s_uuid, uuid)) {
ofs->fs[i].bad_uuid = true;
return false;
}
@ -1342,10 +1343,12 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
/*
* All lower layers that share the same fs as upper layer, use the real
* upper st_dev.
* is_lower will be set if upper fs is shared with a lower layer.
*/
if (ofs->upper_mnt) {
ofs->fs[0].sb = ofs->upper_mnt->mnt_sb;
ofs->fs[0].pseudo_dev = ofs->upper_mnt->mnt_sb->s_dev;
ofs->fs[0].is_lower = false;
}
for (i = 0; i < numlower; i++) {
@ -1387,6 +1390,7 @@ static int ovl_get_layers(struct super_block *sb, struct ovl_fs *ofs,
ofs->layers[ofs->numlayer].fsid = fsid;
ofs->layers[ofs->numlayer].fs = &ofs->fs[fsid];
ofs->numlayer++;
ofs->fs[fsid].is_lower = true;
}
/*