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Subject[PATCH 4.18 108/235] ovl: fix oopses in ovl_fill_super() failure paths
Date
4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Miklos Szeredi <mszeredi@redhat.com>

commit 8c25741aaad8be6fbe51510e917c740e0059cf83 upstream.

ovl_free_fs() dereferences ofs->workbasedir and ofs->upper_mnt in cases when
those might not have been initialized yet.

Fix the initialization order for these fields.

Reported-by: syzbot+c75f181dc8429d2eb887@syzkaller.appspotmail.com
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: <stable@vger.kernel.org> # v4.15
Fixes: 95e6d4177cb7 ("ovl: grab reference to workbasedir early")
Fixes: a9075cdb467d ("ovl: factor out ovl_free_fs() helper")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/overlayfs/super.c | 26 ++++++++++++++------------
1 file changed, 14 insertions(+), 12 deletions(-)

--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -970,16 +970,6 @@ static int ovl_get_upper(struct ovl_fs *
if (err)
goto out;

- err = -EBUSY;
- if (ovl_inuse_trylock(upperpath->dentry)) {
- ofs->upperdir_locked = true;
- } else if (ofs->config.index) {
- pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
- goto out;
- } else {
- pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
- }
-
upper_mnt = clone_private_mount(upperpath);
err = PTR_ERR(upper_mnt);
if (IS_ERR(upper_mnt)) {
@@ -990,6 +980,17 @@ static int ovl_get_upper(struct ovl_fs *
/* Don't inherit atime flags */
upper_mnt->mnt_flags &= ~(MNT_NOATIME | MNT_NODIRATIME | MNT_RELATIME);
ofs->upper_mnt = upper_mnt;
+
+ err = -EBUSY;
+ if (ovl_inuse_trylock(ofs->upper_mnt->mnt_root)) {
+ ofs->upperdir_locked = true;
+ } else if (ofs->config.index) {
+ pr_err("overlayfs: upperdir is in-use by another mount, mount with '-o index=off' to override exclusive upperdir protection.\n");
+ goto out;
+ } else {
+ pr_warn("overlayfs: upperdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
+ }
+
err = 0;
out:
return err;
@@ -1089,8 +1090,10 @@ static int ovl_get_workdir(struct ovl_fs
goto out;
}

+ ofs->workbasedir = dget(workpath.dentry);
+
err = -EBUSY;
- if (ovl_inuse_trylock(workpath.dentry)) {
+ if (ovl_inuse_trylock(ofs->workbasedir)) {
ofs->workdir_locked = true;
} else if (ofs->config.index) {
pr_err("overlayfs: workdir is in-use by another mount, mount with '-o index=off' to override exclusive workdir protection.\n");
@@ -1099,7 +1102,6 @@ static int ovl_get_workdir(struct ovl_fs
pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
}

- ofs->workbasedir = dget(workpath.dentry);
err = ovl_make_workdir(ofs, &workpath);
if (err)
goto out;

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