On Wed, Nov 25, 2020 at 12:46 PM Sargun Dhillon <sargun@xxxxxxxxx> wrote: > > Overlayfs added the ability to setup mounts where all syncs could be > short-circuted in (2a99ddacee43: ovl: provide a mount option "volatile"). > > A user might want to remount this fs, but we do not let the user because > of the "incompat" detection feature. In the case of volatile, it is safe > to do something like[1]: > > $ sync -f /root/upperdir > $ rm -rf /root/workdir/incompat/volatile > > There are two ways to go about this. You can call sync on the underlying > filesystem, check the error code, and delete the dirty file if everything > is clean. If you're running lots of containers on the same filesystem, or > you want to avoid all unnecessary I/O, this may be suboptimal. > > Alternatively, you can blindly delete the dirty file, and "hope for the > best". > > This patch introduces transparent functionality to check if it is > (relatively) safe to reuse the upperdir. It ensures that the filesystem > hasn't been remounted, the system hasn't been rebooted, nor has the > overlayfs code changed. Since the structure is explicitly not meant to be > used between different versions of the code, its stability does not matter > so much. > Looks good. You forgot to allow reuse only as volatile... Other than that just a few comments. > [1]: https://lore.kernel.org/linux-unionfs/CAOQ4uxhKr+j5jFyEC2gJX8E8M19mQ3CqdTYaPZOvDQ9c0qLEzw@xxxxxxxxxxxxxx/T/#m6abe713e4318202ad57f301bf28a414e1d824f9c > > Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx> > Cc: linux-fsdevel@xxxxxxxxxxxxxxx > Cc: linux-unionfs@xxxxxxxxxxxxxxx > Cc: Miklos Szeredi <miklos@xxxxxxxxxx> > Cc: Amir Goldstein <amir73il@xxxxxxxxx> > --- > Documentation/filesystems/overlayfs.rst | 6 +- > fs/overlayfs/overlayfs.h | 37 ++++++++++- > fs/overlayfs/readdir.c | 88 +++++++++++++++++++++---- > fs/overlayfs/super.c | 74 ++++++++++++++++----- > fs/overlayfs/util.c | 2 + > 5 files changed, 175 insertions(+), 32 deletions(-) > > diff --git a/Documentation/filesystems/overlayfs.rst b/Documentation/filesystems/overlayfs.rst > index 580ab9a0fe31..18237c79fb4e 100644 > --- a/Documentation/filesystems/overlayfs.rst > +++ b/Documentation/filesystems/overlayfs.rst > @@ -581,7 +581,11 @@ checks for this directory and refuses to mount if present. This is a strong > indicator that user should throw away upper and work directories and create > fresh one. In very limited cases where the user knows that the system has > not crashed and contents of upperdir are intact, The "volatile" directory > -can be removed. > +can be removed. In some cases, the filesystem can detect if the upperdir > +can be reused safely in a subsequent volatile mount. If the filesystem is able > +to determine this, it will not require the user to manually delete the volatile > +directory and mounting will proceed as normal. > + > > Testsuite > --------- > diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h > index f8880aa2ba0e..de694ee99d7c 100644 > --- a/fs/overlayfs/overlayfs.h > +++ b/fs/overlayfs/overlayfs.h > @@ -32,8 +32,13 @@ enum ovl_xattr { > OVL_XATTR_NLINK, > OVL_XATTR_UPPER, > OVL_XATTR_METACOPY, > + OVL_XATTR_VOLATILE, > }; > > +#define OVL_INCOMPATDIR_NAME "incompat" > +#define OVL_VOLATILEDIR_NAME "volatile" > +#define OVL_VOLATILE_DIRTY_NAME "dirty" > + > enum ovl_inode_flag { > /* Pure upper dir that may contain non pure upper entries */ > OVL_IMPURE, > @@ -57,6 +62,31 @@ enum { > OVL_XINO_ON, > }; > > +/* > + * This is copied into the volatile xattr, and the user does not interact with > + * it. There is no stability requirement, as a reboot explicitly invalidates > + * a volatile workdir. It is explicitly meant not to be a stable api. > + * > + * Although this structure isn't meant to be stable it is exposed to potentially > + * unprivileged users. We don't do any kind of cryptographic operations with > + * the structure, so it could be tampered with, or inspected. Don't put > + * kernel memory pointers in it, or anything else that could cause problems, > + * or information disclosure. > + */ > +struct ovl_volatile_info { > + /* > + * This uniquely identifies a boot, and is reset if overlayfs itself > + * is reloaded. Therefore we check our current / known boot_id > + * against this before looking at any other fields to validate: > + * 1. Is this datastructure laid out in the way we expect? (Overlayfs > + * module, reboot, etc...) > + * 2. Could something have changed (like the s_instance_id counter > + * resetting) > + */ > + uuid_t ovl_boot_id; /* Must stay first member */ > + u64 s_instance_id; > +} __packed; > + > /* > * The tuple (fh,uuid) is a universal unique identifier for a copy up origin, > * where: > @@ -422,8 +452,8 @@ void ovl_cleanup_whiteouts(struct dentry *upper, struct list_head *list); > void ovl_cache_free(struct list_head *list); > void ovl_dir_cache_free(struct inode *inode); > int ovl_check_d_type_supported(struct path *realpath); > -int ovl_workdir_cleanup(struct inode *dir, struct vfsmount *mnt, > - struct dentry *dentry, int level); > +int ovl_workdir_cleanup(struct ovl_fs *ofs, struct inode *dir, > + struct vfsmount *mnt, struct dentry *dentry, int level); > int ovl_indexdir_cleanup(struct ovl_fs *ofs); > > /* inode.c */ > @@ -520,3 +550,6 @@ int ovl_set_origin(struct dentry *dentry, struct dentry *lower, > > /* export.c */ > extern const struct export_operations ovl_export_operations; > + > +/* super.c */ > +extern uuid_t ovl_boot_id; > diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c > index 01620ebae1bd..4e3e2bc3ea43 100644 > --- a/fs/overlayfs/readdir.c > +++ b/fs/overlayfs/readdir.c > @@ -1080,10 +1080,68 @@ int ovl_check_d_type_supported(struct path *realpath) > > return rdd.d_type_supported; > } > +static int ovl_verify_volatile_info(struct ovl_fs *ofs, > + struct dentry *volatiledir) > +{ > + int err; > + struct ovl_volatile_info info; > + > + err = ovl_do_getxattr(ofs, volatiledir, OVL_XATTR_VOLATILE, &info, > + sizeof(info)); > + if (err < 0) { > + pr_debug("Unable to read volatile xattr: %d\n", err); > + return -EINVAL; > + } > + > + if (err != sizeof(info)) { > + pr_debug("ovl_volatile_info is of size %d expected %ld\n", err, > + sizeof(info)); > + return -EINVAL; > + } > + > + if (!uuid_equal(&ovl_boot_id, &info.ovl_boot_id)) { > + pr_debug("boot id has changed (reboot or module reloaded)\n"); > + return -EINVAL; > + } > + > + if (volatiledir->d_sb->s_instance_id != info.s_instance_id) { > + pr_debug("workdir has been unmounted and remounted\n"); > + return -EINVAL; > + } > > -#define OVL_INCOMPATDIR_NAME "incompat" > + return 1; > +} > > -static int ovl_workdir_cleanup_recurse(struct path *path, int level) > +/* > + * ovl_check_incompat checks this specific incompat entry for incompatibility. > + * If it is found to be incompatible -EINVAL will be returned. > + * > + * If the directory should be preserved, then this function returns 1. > + */ > +static int ovl_check_incompat(struct ovl_fs *ofs, struct ovl_cache_entry *p, > + struct path *path) > +{ > + int err = -EINVAL; > + struct dentry *d; > + if p->name is not OVL_VOLATILEDIR_NAME, there is no reason to lookup and unless ofs->config.ovl_volatile, you can already fail the check. > + d = lookup_one_len(p->name, path->dentry, p->len); > + if (IS_ERR(d)) > + return PTR_ERR(d); > + > + if (!strcmp(p->name, OVL_VOLATILEDIR_NAME)) > + err = ovl_verify_volatile_info(ofs, d); > + > + if (err == -EINVAL) > + pr_err("incompat feature '%s' cannot be mounted\n", p->name); > + else > + pr_debug("incompat '%s' handled: %d\n", p->name, err); > + > + dput(d); > + return err; > +} > + > +static int ovl_workdir_cleanup_recurse(struct ovl_fs *ofs, struct path *path, > + int level) > { > int err; > struct inode *dir = path->dentry->d_inode; > @@ -1125,16 +1183,19 @@ static int ovl_workdir_cleanup_recurse(struct path *path, int level) > if (p->len == 2 && p->name[1] == '.') > continue; > } else if (incompat) { > - pr_err("overlay with incompat feature '%s' cannot be mounted\n", > - p->name); > - err = -EINVAL; > - break; > + err = ovl_check_incompat(ofs, p, path); > + if (err < 0) > + break; > + /* Skip cleaning this */ > + if (err == 1) > + continue; > } > dentry = lookup_one_len(p->name, path->dentry, p->len); > if (IS_ERR(dentry)) > continue; > if (dentry->d_inode) > - err = ovl_workdir_cleanup(dir, path->mnt, dentry, level); > + err = ovl_workdir_cleanup(ofs, dir, path->mnt, dentry, > + level); > dput(dentry); > if (err) > break; > @@ -1142,11 +1203,13 @@ static int ovl_workdir_cleanup_recurse(struct path *path, int level) > inode_unlock(dir); > out: > ovl_cache_free(&list); > + if (incompat && err >= 0) > + return 1; > return err; > } > > -int ovl_workdir_cleanup(struct inode *dir, struct vfsmount *mnt, > - struct dentry *dentry, int level) > +int ovl_workdir_cleanup(struct ovl_fs *ofs, struct inode *dir, > + struct vfsmount *mnt, struct dentry *dentry, int level) > { > int err; > > @@ -1159,7 +1222,7 @@ int ovl_workdir_cleanup(struct inode *dir, struct vfsmount *mnt, > struct path path = { .mnt = mnt, .dentry = dentry }; > > inode_unlock(dir); > - err = ovl_workdir_cleanup_recurse(&path, level + 1); > + err = ovl_workdir_cleanup_recurse(ofs, &path, level + 1); > inode_lock_nested(dir, I_MUTEX_PARENT); > if (!err) > err = ovl_cleanup(dir, dentry); > @@ -1206,9 +1269,10 @@ int ovl_indexdir_cleanup(struct ovl_fs *ofs) > } > /* Cleanup leftover from index create/cleanup attempt */ > if (index->d_name.name[0] == '#') { > - err = ovl_workdir_cleanup(dir, path.mnt, index, 1); > - if (err) > + err = ovl_workdir_cleanup(ofs, dir, path.mnt, index, 1); > + if (err < 0) > break; > + err = 0; > goto next; > } > err = ovl_verify_index(ofs, index); > diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c > index 290983bcfbb3..9a1b07907662 100644 > --- a/fs/overlayfs/super.c > +++ b/fs/overlayfs/super.c > @@ -15,6 +15,7 @@ > #include <linux/seq_file.h> > #include <linux/posix_acl_xattr.h> > #include <linux/exportfs.h> > +#include <linux/uuid.h> > #include "overlayfs.h" > > MODULE_AUTHOR("Miklos Szeredi <miklos@xxxxxxxxxx>"); > @@ -23,6 +24,7 @@ MODULE_LICENSE("GPL"); > > > struct ovl_dir_cache; > +uuid_t ovl_boot_id; > > #define OVL_MAX_STACK 500 > > @@ -722,20 +724,24 @@ static struct dentry *ovl_workdir_create(struct ovl_fs *ofs, > goto out_unlock; > > retried = true; > - err = ovl_workdir_cleanup(dir, mnt, work, 0); > - dput(work); > - if (err == -EINVAL) { > - work = ERR_PTR(err); > - goto out_unlock; > + err = ovl_workdir_cleanup(ofs, dir, mnt, work, 0); > + /* check if we should reuse the workdir */ > + if (err != 1) { > + dput(work); > + if (err == -EINVAL) { > + work = ERR_PTR(err); > + goto out_unlock; > + } > + goto retry; > } > - goto retry; > + } else { > + work = ovl_create_real(dir, work, > + OVL_CATTR(attr.ia_mode)); > + err = PTR_ERR(work); > + if (IS_ERR(work)) > + goto out_err; > } > > - work = ovl_create_real(dir, work, OVL_CATTR(attr.ia_mode)); > - err = PTR_ERR(work); > - if (IS_ERR(work)) > - goto out_err; > - > /* > * Try to remove POSIX ACL xattrs from workdir. We are good if: > * > @@ -1237,26 +1243,59 @@ static struct dentry *ovl_lookup_or_create(struct dentry *parent, > return child; > } > > +static int ovl_set_volatile_info(struct ovl_fs *ofs, struct dentry *volatiledir) > +{ > + int err; > + struct ovl_volatile_info info = { > + .s_instance_id = volatiledir->d_sb->s_instance_id, > + }; > + > + uuid_copy(&info.ovl_boot_id, &ovl_boot_id); > + err = ovl_do_setxattr(ofs, volatiledir, OVL_XATTR_VOLATILE, &info, > + sizeof(info)); > + > + if (err == -EOPNOTSUPP) > + return 0; > + > + return err; > +} > + > /* > * Creates $workdir/work/incompat/volatile/dirty file if it is not already > * present. > */ > static int ovl_create_volatile_dirty(struct ovl_fs *ofs) > { > + int err; > unsigned int ctr; > - struct dentry *d = dget(ofs->workbasedir); > + struct dentry *volatiledir, *d = dget(ofs->workbasedir); > static const char *const volatile_path[] = { > - OVL_WORKDIR_NAME, "incompat", "volatile", "dirty" > + OVL_WORKDIR_NAME, > + OVL_INCOMPATDIR_NAME, > + OVL_VOLATILEDIR_NAME, > + OVL_VOLATILE_DIRTY_NAME, > }; > const char *const *name = volatile_path; > > - for (ctr = ARRAY_SIZE(volatile_path); ctr; ctr--, name++) { > - d = ovl_lookup_or_create(d, *name, ctr > 1 ? S_IFDIR : S_IFREG); > + /* Stop before the dirty file is created */ > + for (ctr = 0; ctr < ARRAY_SIZE(volatile_path) - 1; ctr++, name++) { > + d = ovl_lookup_or_create(d, *name, S_IFDIR); > if (IS_ERR(d)) > return PTR_ERR(d); > } > - dput(d); > - return 0; > + volatiledir = dget(d); > + > + /* Create the dirty file exists before we set the xattr */ > + d = ovl_lookup_or_create(d, *name, S_IFREG); There is really no point in including OVL_VOLATILE_DIRTY_NAME in the array this is just too confusing, use the name explicitly. Thanks, Amir.
