From: Amir Goldstein amir73il@gmail.com
commit 0be0bfd2de9dfdd2098a9c5b14bdd8f739c9165d upstream.
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@veci.piliscsaba... Link: https://github.com/containers/libpod/issues/3540 Fixes: 146d62e5a586 ("ovl: detect overlapping layers") Cc: stable@vger.kernel.org # v4.19+ Signed-off-by: Amir Goldstein amir73il@gmail.com Tested-by: Colin Walters walters@verbum.org Signed-off-by: Miklos Szeredi mszeredi@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- Documentation/filesystems/overlayfs.txt | 2 fs/overlayfs/ovl_entry.h | 1 fs/overlayfs/super.c | 73 ++++++++++++++++++++------------ 3 files changed, 49 insertions(+), 27 deletions(-)
--- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -302,7 +302,7 @@ beneath or above the path of another ove
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. --- 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 */ --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -212,6 +212,7 @@ static void ovl_free_fs(struct ovl_fs *o { 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_b 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_bl 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_
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 s 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 @@ out_err: * - 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_
/* 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( 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( * 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;