On Thu, Mar 29, 2018 at 10:38 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote:
> This patch modifies ovl_lookup() and friends to lookup metacopy dentries.
> It also allows for presence of metacopy dentries in lower layer.
>
> During lookup, check for presence of OVL_XATTR_METACOPY and if not present,
> set OVL_UPPERDATA bit in flags.
>
> We don't support metacopy feature with nfs_export. So in nfs_export code,
> we set OVL_UPPERDATA flag set unconditionally if upper inode exists.
>
> Do not follow metacopy origin if we find a metacopy only inode and metacopy
> feature is not enabled for that mount. Like redirect, this can have security
> implications where an attacker could hand craft upper and try to gain
> access to file on lower which it should not have to begin with.
>
> Signed-off-by: Vivek Goyal <vgoyal@xxxxxxxxxx>
> ---
> fs/overlayfs/export.c | 3 ++
> fs/overlayfs/inode.c | 6 +++-
> fs/overlayfs/namei.c | 90 ++++++++++++++++++++++++++++++++++++++++++------
> fs/overlayfs/overlayfs.h | 1 +
> fs/overlayfs/util.c | 22 ++++++++++++
> 5 files changed, 110 insertions(+), 12 deletions(-)
>
> diff --git a/fs/overlayfs/export.c b/fs/overlayfs/export.c
> index e668329f7361..1c233096e59c 100644
> --- a/fs/overlayfs/export.c
> +++ b/fs/overlayfs/export.c
> @@ -311,6 +311,9 @@ static struct dentry *ovl_obtain_alias(struct super_block *sb,
> return ERR_CAST(inode);
> }
>
> + if (upper)
> + ovl_set_flag(OVL_UPPERDATA, inode);
> +
> dentry = d_find_any_alias(inode);
> if (!dentry) {
> dentry = d_alloc_anon(inode->i_sb);
> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
> index 3991a890b464..e1dbfed0c449 100644
> --- a/fs/overlayfs/inode.c
> +++ b/fs/overlayfs/inode.c
> @@ -677,7 +677,7 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
> struct inode *realinode = upperdentry ? d_inode(upperdentry) : NULL;
> struct inode *inode;
> bool bylower = ovl_hash_bylower(sb, upperdentry, lowerdentry, index);
> - bool is_dir;
> + bool is_dir, metacopy = false;
>
> if (!realinode)
> realinode = d_inode(lowerdentry);
> @@ -732,6 +732,10 @@ struct inode *ovl_get_inode(struct super_block *sb, struct dentry *upperdentry,
> if (index)
> ovl_set_flag(OVL_INDEX, inode);
>
> + metacopy = ovl_check_metacopy_xattr(upperdentry ?: lowerdentry);
No reason to check metacopy on lowerdentry.
> + if (upperdentry && !metacopy)
> + ovl_set_flag(OVL_UPPERDATA, inode);
> +
> OVL_I(inode)->redirect = redirect;
>
> /* Check for non-merge dir that may have whiteouts */
> diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c
> index 0b325e65864c..1dba89e9543f 100644
> --- a/fs/overlayfs/namei.c
> +++ b/fs/overlayfs/namei.c
> @@ -24,6 +24,7 @@ struct ovl_lookup_data {
> bool stop;
> bool last;
> char *redirect;
> + bool metacopy;
> };
>
> static int ovl_check_redirect(struct dentry *dentry, struct ovl_lookup_data *d,
> @@ -252,9 +253,13 @@ static int ovl_lookup_single(struct dentry *base, struct ovl_lookup_data *d,
> goto put_and_out;
> }
> if (!d_can_lookup(this)) {
> - d->stop = true;
upper was a dir. You look in lower and find a non-dir. you need to stop
going to next layer. goto put_and_out won't do that.
Similarly, you need to handle the case where dir is found below
non-dir with metacopy.
> if (d->is_dir)
> goto put_and_out;
> + err = ovl_check_metacopy_xattr(this);
> + if (err < 0)
> + goto out_err;
> + d->stop = !err;
> + d->metacopy = !!err;
> goto out;
> }
> if (last_element)
> @@ -815,7 +820,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> 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 ovl_path *stack = NULL;
> + struct ovl_path *stack = NULL, *origin_path = NULL;
> struct dentry *upperdir, *upperdentry = NULL;
> struct dentry *origin = NULL;
> struct dentry *index = NULL;
> @@ -826,6 +831,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> struct dentry *this;
> unsigned int i;
> int err;
> + bool metacopy = false;
> struct ovl_lookup_data d = {
> .name = dentry->d_name,
> .is_dir = false,
> @@ -833,6 +839,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> .stop = false,
> .last = ofs->config.redirect_follow ? false : !poe->numlower,
> .redirect = NULL,
> + .metacopy = false,
> };
>
> if (dentry->d_name.len > ofs->namelen)
> @@ -851,7 +858,8 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> goto out;
> }
> if (upperdentry && !d.is_dir) {
> - BUG_ON(!d.stop || d.redirect);
> + unsigned int origin_ctr = 0;
> + BUG_ON(d.redirect);
> /*
> * Lookup copy up origin by decoding origin file handle.
> * We may get a disconnected dentry, which is fine,
> @@ -862,16 +870,20 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> * number - it's the same as if we held a reference
> * to a dentry in lower layer that was moved under us.
> */
> - err = ovl_check_origin(ofs, upperdentry, &stack, &ctr);
> + err = ovl_check_origin(ofs, upperdentry, &origin_path,
> + &origin_ctr);
> if (err)
> goto out_put_upper;
> +
> + if (d.metacopy)
> + metacopy = true;
> }
>
> if (d.redirect) {
> err = -ENOMEM;
> upperredirect = kstrdup(d.redirect, GFP_KERNEL);
> if (!upperredirect)
> - goto out_put_upper;
> + goto out_put_origin;
> if (d.redirect[0] == '/')
> poe = roe;
> }
> @@ -883,7 +895,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> stack = kcalloc(ofs->numlower, sizeof(struct ovl_path),
> GFP_KERNEL);
> if (!stack)
> - goto out_put_upper;
> + goto out_put_origin;
> }
>
> for (i = 0; !d.stop && i < poe->numlower; i++) {
> @@ -905,7 +917,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> * If no origin fh is stored in upper of a merge dir, store fh
> * of lower dir and set upper parent "impure".
> */
> - if (upperdentry && !ctr && !ofs->noxattr) {
> + if (upperdentry && !ctr && !ofs->noxattr && d.is_dir) {
> err = ovl_fix_origin(dentry, this, upperdentry);
> if (err) {
> dput(this);
> @@ -917,16 +929,35 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> * When "verify_lower" feature is enabled, do not merge with a
> * lower dir that does not match a stored origin xattr. In any
> * case, only verified origin is used for index lookup.
> + *
> + * For non-dir dentry, make sure dentry found by lookup
> + * matches the origin stored in upper. Otherwise its an
> + * error.
> */
> - if (upperdentry && !ctr && ovl_verify_lower(dentry->d_sb)) {
> + if (upperdentry && !ctr &&
> + ((d.is_dir && ovl_verify_lower(dentry->d_sb)) ||
> + (!d.is_dir && origin_path))) {
> err = ovl_verify_origin(upperdentry, this, false);
> if (err) {
> dput(this);
> - break;
> + if (d.is_dir)
> + break;
> + goto out_put;
> }
> -
> /* Bless lower dir as verified origin */
> - origin = this;
> + if (d.is_dir)
> + origin = this;
It's ok to bless verified non-dir as well.
It is going to be blesses anyway, just above index lookup if ctr > 0.
> + }
> +
> + if (d.metacopy)
> + metacopy = true;
> + /*
> + * Do not store intermediate metacopy dentries in chain,
> + * except top most lower metacopy dentry
> + */
> + if (d.metacopy && ctr) {
> + dput(this);
> + continue;
> }
>
> stack[ctr].dentry = this;
> @@ -960,6 +991,34 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> }
> }
>
> + if (metacopy) {
> + BUG_ON(d.is_dir);
Yeh, I think that is really a bug, because you need to detect
the case of dir in lower layer under metacopy in upper layer
and do something about it.
> + /*
> + * Found a metacopy dentry but did not find corresponding
> + * data dentry
> + */
> + if (d.metacopy) {
> + err = -ESTALE;
> + goto out_put;
> + }
> +
> + err = -EPERM;
> + if (!ofs->config.metacopy) {
> + pr_warn_ratelimited("overlay: refusing to follow"
> + " metacopy origin for (%pd2)\n",
> + dentry);
> + goto out_put;
> + }
> + } else if (!d.is_dir && upperdentry && !ctr && origin_path) {
> + if (WARN_ON(stack != NULL)) {
> + err = -EIO;
> + goto out_put;
> + }
> + stack = origin_path;
> + ctr = 1;
> + origin_path = NULL;
> + }
> +
> /*
> * Lookup index by lower inode and verify it matches upper inode.
> * We only trust dir index if we verified that lower dir matches
> @@ -1006,6 +1065,10 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> }
>
> revert_creds(old_cred);
> + if (origin_path) {
> + dput(origin_path->dentry);
> + kfree(origin_path);
> + }
> dput(index);
> kfree(stack);
> kfree(d.redirect);
> @@ -1019,6 +1082,11 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
> for (i = 0; i < ctr; i++)
> dput(stack[i].dentry);
> kfree(stack);
> +out_put_origin:
> + if (origin_path) {
> + dput(origin_path->dentry);
> + kfree(origin_path);
> + }
There is no need for the new goto label.
Just add this in existing out_put_upper label.
Thanks,
Amir,
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