On Fri, Jul 12, 2019 at 3:24 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote:
>
> Once upon a time, commit 2cac0c00a6cd ("ovl: get exclusive ownership on
> upper/work dirs") in v4.13 added some sanity checks on overlayfs layers.
> This change caused a docker regression. The root cause was mount leaks
> by docker, which as far as I know, still exist.
>
> To mitigate the regression, commit 85fdee1eef1a ("ovl: fix regression
> caused by exclusive upper/work dir protection") in v4.14 turned the
> mount errors into warnings for the default index=off configuration.
>
> Recently, commit 146d62e5a586 ("ovl: detect overlapping layers") in
> v5.2, re-introduced exclusive upper/work dir checks regardless of
> index=off configuration.
>
> This changes the status quo and mount leak related bug reports have
> started to re-surface. Restore the status quo to fix the regressions.
> To clarify, index=off does NOT relax overlapping layers check for this
> ovelayfs mount. index=off only relaxes exclusive upper/work dir checks
> with another overlayfs mount.
>
> To cover the part of overlapping layers detection that used the
> exclusive upper/work dir checks to detect overlap with self upper/work
> dir, add a trap also on the work base dir.
>
> Link: https://github.com/moby/moby/issues/34672
> Link: https://lore.kernel.org/linux-fsdevel/20171006121405.GA32700@xxxxxxxxxxxxxxxxxxxxxxxxxx/
> Link: https://github.com/containers/libpod/issues/3540
> Fixes: 146d62e5a586 ("ovl: detect overlapping layers")
> Cc: <stable@xxxxxxxxxxxxxxx> # v4.19+
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
Miklos,
Please add:
Tested-by: Colin Walters <walters@xxxxxxxxxx>
Thanks,
Amir.
> ---
>
> Miklos,
>
> This showed up initially on libpod github and since then also surfaced
> in coreos who have merged some band aid fix for their kernel.
> I bet docker users will start noticing this soon as well.
>
> I have modified xfstest overlay/065 to accomodate these changes and will
> post the patch later.
>
> Thanks,
> Amir.
>
> Documentation/filesystems/overlayfs.txt | 2 +-
> fs/overlayfs/ovl_entry.h | 1 +
> fs/overlayfs/super.c | 73 ++++++++++++++++---------
> 3 files changed, 49 insertions(+), 27 deletions(-)
>
> diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
> index 1da2f1668f08..845d689e0fd7 100644
> --- a/Documentation/filesystems/overlayfs.txt
> +++ b/Documentation/filesystems/overlayfs.txt
> @@ -302,7 +302,7 @@ beneath or above the path of another overlay lower layer path.
>
> Using an upper layer path and/or a workdir path that are already used by
> another overlay mount is not allowed and may fail with EBUSY. Using
> -partially overlapping paths is not allowed but will not fail with EBUSY.
> +partially overlapping paths is not allowed and may fail with EBUSY.
> If files are accessed from two overlayfs mounts which share or overlap the
> upper layer and/or workdir path the behavior of the overlay is undefined,
> though it will not result in a crash or deadlock.
> diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
> index 28a2d12a1029..a8279280e88d 100644
> --- a/fs/overlayfs/ovl_entry.h
> +++ b/fs/overlayfs/ovl_entry.h
> @@ -66,6 +66,7 @@ struct ovl_fs {
> bool workdir_locked;
> /* Traps in ovl inode cache */
> struct inode *upperdir_trap;
> + struct inode *workbasedir_trap;
> struct inode *workdir_trap;
> struct inode *indexdir_trap;
> /* Inode numbers in all layers do not use the high xino_bits */
> diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
> index b368e2e102fa..afbcb116a7f1 100644
> --- a/fs/overlayfs/super.c
> +++ b/fs/overlayfs/super.c
> @@ -212,6 +212,7 @@ static void ovl_free_fs(struct ovl_fs *ofs)
> {
> unsigned i;
>
> + iput(ofs->workbasedir_trap);
> iput(ofs->indexdir_trap);
> iput(ofs->workdir_trap);
> iput(ofs->upperdir_trap);
> @@ -1003,6 +1004,25 @@ static int ovl_setup_trap(struct super_block *sb, struct dentry *dir,
> return 0;
> }
>
> +/*
> + * Determine how we treat concurrent use of upperdir/workdir based on the
> + * index feature. This is papering over mount leaks of container runtimes,
> + * for example, an old overlay mount is leaked and now its upperdir is
> + * attempted to be used as a lower layer in a new overlay mount.
> + */
> +static int ovl_report_in_use(struct ovl_fs *ofs, const char *name)
> +{
> + if (ofs->config.index) {
> + pr_err("overlayfs: %s is in-use as upperdir/workdir of another mount, mount with '-o index=off' to override exclusive upperdir protection.\n",
> + name);
> + return -EBUSY;
> + } else {
> + pr_warn("overlayfs: %s is in-use as upperdir/workdir of another mount, accessing files from both mounts will result in undefined behavior.\n",
> + name);
> + return 0;
> + }
> +}
> +
> static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
> struct path *upperpath)
> {
> @@ -1040,14 +1060,12 @@ static int ovl_get_upper(struct super_block *sb, struct ovl_fs *ofs,
> 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 = ovl_report_in_use(ofs, "upperdir");
> + if (err)
> + goto out;
> }
>
> err = 0;
> @@ -1157,16 +1175,19 @@ static int ovl_get_workdir(struct super_block *sb, struct ovl_fs *ofs,
>
> ofs->workbasedir = dget(workpath.dentry);
>
> - err = -EBUSY;
> 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");
> - goto out;
> } else {
> - pr_warn("overlayfs: workdir is in-use by another mount, accessing files from both mounts will result in undefined behavior.\n");
> + err = ovl_report_in_use(ofs, "workdir");
> + if (err)
> + goto out;
> }
>
> + err = ovl_setup_trap(sb, ofs->workbasedir, &ofs->workbasedir_trap,
> + "workdir");
> + if (err)
> + goto out;
> +
> err = ovl_make_workdir(sb, ofs, &workpath);
>
> out:
> @@ -1313,16 +1334,16 @@ static int ovl_get_lower_layers(struct super_block *sb, struct ovl_fs *ofs,
> if (err < 0)
> goto out;
>
> - err = -EBUSY;
> - if (ovl_is_inuse(stack[i].dentry)) {
> - pr_err("overlayfs: lowerdir is in-use as upperdir/workdir\n");
> - goto out;
> - }
> -
> err = ovl_setup_trap(sb, stack[i].dentry, &trap, "lowerdir");
> if (err)
> goto out;
>
> + if (ovl_is_inuse(stack[i].dentry)) {
> + err = ovl_report_in_use(ofs, "lowerdir");
> + if (err)
> + goto out;
> + }
> +
> mnt = clone_private_mount(&stack[i]);
> err = PTR_ERR(mnt);
> if (IS_ERR(mnt)) {
> @@ -1469,8 +1490,8 @@ static struct ovl_entry *ovl_get_lowerstack(struct super_block *sb,
> * - another layer of this overlayfs instance
> * - upper/work dir of any overlayfs instance
> */
> -static int ovl_check_layer(struct super_block *sb, struct dentry *dentry,
> - const char *name)
> +static int ovl_check_layer(struct super_block *sb, struct ovl_fs *ofs,
> + struct dentry *dentry, const char *name)
> {
> struct dentry *next = dentry, *parent;
> int err = 0;
> @@ -1482,13 +1503,11 @@ static int ovl_check_layer(struct super_block *sb, struct dentry *dentry,
>
> /* Walk back ancestors to root (inclusive) looking for traps */
> while (!err && parent != next) {
> - if (ovl_is_inuse(parent)) {
> - err = -EBUSY;
> - pr_err("overlayfs: %s path overlapping in-use upperdir/workdir\n",
> - name);
> - } else if (ovl_lookup_trap_inode(sb, parent)) {
> + if (ovl_lookup_trap_inode(sb, parent)) {
> err = -ELOOP;
> pr_err("overlayfs: overlapping %s path\n", name);
> + } else if (ovl_is_inuse(parent)) {
> + err = ovl_report_in_use(ofs, name);
> }
> next = parent;
> parent = dget_parent(next);
> @@ -1509,7 +1528,8 @@ static int ovl_check_overlapping_layers(struct super_block *sb,
> int i, err;
>
> if (ofs->upper_mnt) {
> - err = ovl_check_layer(sb, ofs->upper_mnt->mnt_root, "upperdir");
> + err = ovl_check_layer(sb, ofs, ofs->upper_mnt->mnt_root,
> + "upperdir");
> if (err)
> return err;
>
> @@ -1520,13 +1540,14 @@ static int ovl_check_overlapping_layers(struct super_block *sb,
> * workbasedir. In that case, we already have their traps in
> * inode cache and we will catch that case on lookup.
> */
> - err = ovl_check_layer(sb, ofs->workbasedir, "workdir");
> + err = ovl_check_layer(sb, ofs, ofs->workbasedir, "workdir");
> if (err)
> return err;
> }
>
> for (i = 0; i < ofs->numlower; i++) {
> - err = ovl_check_layer(sb, ofs->lower_layers[i].mnt->mnt_root,
> + err = ovl_check_layer(sb, ofs,
> + ofs->lower_layers[i].mnt->mnt_root,
> "lowerdir");
> if (err)
> return err;
> --
> 2.17.1
>
