On Mon, Apr 24, 2017 at 11:14 AM, Amir Goldstein <amir73il@xxxxxxxxx> wrote:
> When overlay.fh xattr is found in a directory inode, instead of lookup
> of the dentry in next lower layer by name, first try to get it by calling
> exportfs_decode_fh().
>
> On failure to lookup by file handle to lower layer, fall back to lookup
> by name with or without path redirect.
>
> For now we only support following by file handle from upper if there is a
> single lower layer, because fallback from lookup by file hande to lookup
> by path in mid layers is not yet implemented.
>
> Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> ---
> fs/overlayfs/namei.c | 185 +++++++++++++++++++++++++++++++++++++++++++----
> fs/overlayfs/overlayfs.h | 1 +
> fs/overlayfs/util.c | 14 ++++
> 3 files changed, 186 insertions(+), 14 deletions(-)
>
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index d660177..0d1cc8f 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -9,9 +9,11 @@
>
> #include <linux/fs.h>
> #include <linux/cred.h>
> +#include <linux/mount.h>
> #include <linux/namei.h>
> #include <linux/xattr.h>
> #include <linux/ratelimit.h>
> +#include <linux/exportfs.h>
> #include "overlayfs.h"
> #include "ovl_entry.h"
>
> @@ -21,7 +23,10 @@ struct ovl_lookup_data {
> bool opaque;
> bool stop;
> bool last;
> - char *redirect;
> + bool by_path; /* redirect by path */
> + bool by_fh; /* redirect by file handle */
> + char *redirect; /* path to follow */
> + struct ovl_fh *fh; /* file handle to follow */
> };
>
> static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> @@ -81,6 +86,42 @@ static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> goto err_free;
> }
>
> +static int ovl_check_redirect_fh(struct dentry *dentry,
> + struct ovl_lookup_data *d)
> +{
> + int res;
> + void *buf = NULL;
> +
> + res = vfs_getxattr(dentry, OVL_XATTR_FH, NULL, 0);
> + if (res < 0) {
> + if (res == -ENODATA || res == -EOPNOTSUPP)
> + return 0;
> + goto fail;
> + }
> + buf = kzalloc(res, GFP_TEMPORARY);
> + if (!buf)
> + return -ENOMEM;
> +
> + if (res == 0)
> + goto fail;
> +
> + res = vfs_getxattr(dentry, OVL_XATTR_FH, buf, res);
> + if (res < 0 || !ovl_redirect_fh_ok(buf, res))
> + goto fail;
> +
> + kfree(d->fh);
> + d->fh = buf;
> +
> + return 0;
> +
> +err_free:
> + kfree(buf);
> + return 0;
> +fail:
> + pr_warn_ratelimited("overlayfs: failed to get file handle (%i)\n", res);
> + goto err_free;
> +}
> +
> static bool ovl_is_opaquedir(struct dentry *dentry)
> {
> int res;
> @@ -96,22 +137,81 @@ static bool ovl_is_opaquedir(struct dentry *dentry)
> return false;
> }
>
> +/* Check if p1 is connected with a chain of hashed dentries to p2 */
> +static bool ovl_is_lookable(struct dentry *p1, struct dentry *p2)
> +{
> + struct dentry *p;
> +
> + for (p = p2; !IS_ROOT(p); p = p->d_parent) {
> + if (d_unhashed(p))
> + return false;
> + if (p->d_parent == p1)
> + return true;
> + }
> + return false;
> +}
Walking the dentry tree without RCU protection is dangerous and broken.
I'm also wondering if there's a better way to find the layer (e.g.
store the layer index in the handle as well).
> +
> +/* Check if dentry is reachable from mnt via path lookup */
> +static int ovl_dentry_under_mnt(void *ctx, struct dentry *dentry)
> +{
> + struct vfsmount *mnt = ctx;
> +
> + return ovl_is_lookable(mnt->mnt_root, dentry);
> +}
> +
> +static struct dentry *ovl_lookup_fh(struct vfsmount *mnt,
> + const struct ovl_fh *fh)
> +{
> + int bytes = (fh->len - offsetof(struct ovl_fh, fid));
> +
> + /*
> + * When redirect_fh is disabled, 'invalid' file handles are stored
> + * to indicate that this entry has been copied up.
> + */
> + if (!bytes || (int)fh->type == FILEID_INVALID)
> + return ERR_PTR(-ESTALE);
> +
> + /*
> + * Several layers can be on the same fs and decoded dentry may be in
> + * either one of those layers. We are looking for a match of dentry
> + * and mnt to find out to which layer the decoded dentry belongs to.
> + */
> + return exportfs_decode_fh(mnt, (struct fid *)fh->fid,
> + bytes >> 2, (int)fh->type,
> + ovl_dentry_under_mnt, mnt);
> +}
> +
> static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> const char *name, unsigned int namelen,
> size_t prelen, const char *post,
> - struct dentry **ret)
> + struct vfsmount *mnt, struct dentry **ret)
I think it would be better to split this function into path and fh
variants and extract the common parts into helper(s).
> {
> struct dentry *this;
> int err;
>
> - this = lookup_one_len_unlocked(name, base, namelen);
> + /*
> + * Lookup of upper is with null d->fh.
> + * Lookup of lower is either by_fh with non-null d->fh
> + * or by_path with null d->fh.
> + */
> + if (d->fh)
> + this = ovl_lookup_fh(mnt, d->fh);
> + else
> + this = lookup_one_len_unlocked(name, base, namelen);
> if (IS_ERR(this)) {
> err = PTR_ERR(this);
> this = NULL;
> if (err == -ENOENT || err == -ENAMETOOLONG)
> goto out;
> + if (d->fh && err == -ESTALE)
> + goto out;
> goto out_err;
> }
> +
> + /* If found by file handle - don't follow that handle again */
> + kfree(d->fh);
> + d->fh = NULL;
> +
> if (!this->d_inode)
> goto put_and_out;
>
> @@ -135,9 +235,18 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> d->stop = d->opaque = true;
> goto out;
> }
> - err = ovl_check_redirect(this, d, prelen, post);
> - if (err)
> - goto out_err;
> + if (d->last)
> + goto out;
> + if (d->by_path) {
> + err = ovl_check_redirect(this, d, prelen, post);
> + if (err)
> + goto out_err;
> + }
> + if (d->by_fh) {
> + err = ovl_check_redirect_fh(this, d);
> + if (err)
> + goto out_err;
> + }
> out:
> *ret = this;
> return 0;
> @@ -152,6 +261,12 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> return err;
> }
>
> +static int ovl_lookup_layer_fh(struct path *path, struct ovl_lookup_data *d,
> + struct dentry **ret)
> +{
> + return ovl_lookup_single(path->dentry, d, "", 0, 0, "", path->mnt, ret);
> +}
> +
> static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
> struct dentry **ret)
> {
> @@ -162,7 +277,7 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
>
> if (d->name.name[0] != '/')
> return ovl_lookup_single(base, d, d->name.name, d->name.len,
> - 0, "", ret);
> + 0, "", NULL, ret);
>
> while (!IS_ERR_OR_NULL(base) && d_can_lookup(base)) {
> const char *s = d->name.name + d->name.len - rem;
> @@ -175,7 +290,7 @@ static int ovl_lookup_layer(struct dentry *base, struct ovl_lookup_data *d,
> return -EIO;
>
> err = ovl_lookup_single(base, d, s, thislen,
> - d->name.len - rem, next, &base);
> + d->name.len - rem, next, NULL, &base);
> dput(dentry);
> if (err)
> return err;
> @@ -220,6 +335,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> const struct cred *old_cred;
> struct ovl_fs *ofs = dentry->d_sb->s_fs_info;
> struct ovl_entry *poe = dentry->d_parent->d_fsdata;
> + struct ovl_entry *roe = dentry->d_sb->s_root->d_fsdata;
> struct path *stack = NULL;
> struct dentry *upperdir, *upperdentry = NULL;
> unsigned int ctr = 0;
> @@ -235,7 +351,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> .opaque = false,
> .stop = false,
> .last = !poe->numlower,
> + .by_path = true,
> .redirect = NULL,
> + .by_fh = true,
> + .fh = NULL,
> };
>
> if (dentry->d_name.len > ofs->namelen)
> @@ -259,13 +378,23 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> if (!upperredirect)
> goto out_put_upper;
> if (d.redirect[0] == '/')
> - poe = dentry->d_sb->s_root->d_fsdata;
> + poe = roe;
> }
> if (d.opaque)
> type |= __OVL_PATH_OPAQUE;
> }
>
> - if (!d.stop && poe->numlower) {
> + /*
> + * For now we only support lower by fh in single layer, because
> + * fallback from lookup by fh to lookup by path in mid layers for
> + * merge directory is not yet implemented.
> + */
> + if (!ofs->redirect_fh || ofs->numlower > 1) {
> + kfree(d.fh);
> + d.fh = NULL;
> + }
> +
> + if (!d.stop && (poe->numlower || d.fh)) {
> err = -ENOMEM;
> stack = kcalloc(ofs->numlower, sizeof(struct path),
> GFP_TEMPORARY);
> @@ -273,6 +402,35 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> goto out_put_upper;
> }
>
> + /* Try to lookup lower layers by file handle */
> + d.by_path = false;
> + for (i = 0; !d.stop && d.fh && i < roe->numlower; i++) {
> + struct path lowerpath = poe->lowerstack[i];
> +
> + d.last = i == poe->numlower - 1;
> + err = ovl_lookup_layer_fh(&lowerpath, &d, &this);
> + if (err)
> + goto out_put;
> +
> + if (!this)
> + continue;
> +
> + stack[ctr].dentry = this;
> + stack[ctr].mnt = lowerpath.mnt;
> + ctr++;
> + /*
> + * Found by fh - won't lookup by path.
> + * TODO: set d.redirect to dentry_path(this),
> + * so lookup can continue by path.
> + */
> + d.stop = true;
> + }
> +
> + /* Fallback to lookup lower layers by path */
> + d.by_path = true;
> + d.by_fh = false;
> + kfree(d.fh);
> + d.fh = NULL;
> for (i = 0; !d.stop && i < poe->numlower; i++) {
> struct path lowerpath = poe->lowerstack[i];
>
> @@ -291,10 +449,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> if (d.stop)
> break;
>
> - if (d.redirect &&
> - d.redirect[0] == '/' &&
> - poe != dentry->d_sb->s_root->d_fsdata) {
> - poe = dentry->d_sb->s_root->d_fsdata;
> + if (d.redirect && d.redirect[0] == '/' && poe != roe) {
> + poe = roe;
>
> /* Find the current layer on the root dentry */
> for (i = 0; i < poe->numlower; i++)
> @@ -354,6 +510,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> dput(upperdentry);
> kfree(upperredirect);
> out:
> + kfree(d.fh);
> kfree(d.redirect);
> revert_creds(old_cred);
> return ERR_PTR(err);
> diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
> index c3cfbc5..08002ce 100644
> --- a/fs/overlayfs/overlayfs.h
> +++ b/fs/overlayfs/overlayfs.h
> @@ -190,6 +190,7 @@ const char *ovl_dentry_get_redirect(struct dentry *dentry);
> void ovl_dentry_set_redirect(struct dentry *dentry, const char *redirect);
> bool ovl_redirect_fh(struct super_block *sb);
> void ovl_clear_redirect_fh(struct super_block *sb);
> +bool ovl_redirect_fh_ok(const char *redirect, size_t size);
> void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
> void ovl_inode_init(struct inode *inode, struct inode *realinode,
> bool is_upper);
> diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
> index b3bc117..dba9753 100644
> --- a/fs/overlayfs/util.c
> +++ b/fs/overlayfs/util.c
> @@ -254,6 +254,20 @@ void ovl_clear_redirect_fh(struct super_block *sb)
> ofs->redirect_fh = false;
> }
>
> +bool ovl_redirect_fh_ok(const char *redirect, size_t size)
> +{
> + struct ovl_fh *fh = (void *)redirect;
> +
> + if (size < sizeof(struct ovl_fh) || size < fh->len)
> + return false;
> +
> + if (fh->version > OVL_FH_VERSION ||
> + fh->magic != OVL_FH_MAGIC)
> + return false;
> +
> + return true;
> +}
> +
> void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry)
> {
> struct ovl_entry *oe = dentry->d_fsdata;
> --
> 2.7.4
>
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