ovl: untangle copy up call chain

In an attempt to dedup ~100 LOC, we ended up creating a tangled call chain,
whose branches merge and diverge in several points according to the
immutable c->tmpfile copy up mode.

This call chain was hard to analyse for locking correctness because the
locking requirements for the c->tmpfile flow were very different from the
locking requirements for the !c->tmpfile flow (i.e. directory vs.  regulare
file copy up).

Split the copy up helpers of the c->tmpfile flow from those of the
!c->tmpfile (i.e. workdir) flow and remove the c->tmpfile mode from copy up
context.

Suggested-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 989782a..618cffc 100644 (file)
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -395,7 +395,6 @@ struct ovl_copy_up_ctx {
        struct dentry *destdir;
        struct qstr destname;
        struct dentry *workdir;
-       bool tmpfile;
        bool origin;
        bool indexed;
        bool metacopy;
@@ -440,62 +439,6 @@ static int ovl_link_up(struct ovl_copy_up_ctx *c)
        return err;
 }
 
-static int ovl_install_temp(struct ovl_copy_up_ctx *c, struct dentry *temp,
-                           struct dentry **newdentry)
-{
-       int err;
-       struct dentry *upper;
-       struct inode *udir = d_inode(c->destdir);
-
-       upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
-       if (IS_ERR(upper))
-               return PTR_ERR(upper);
-
-       if (c->tmpfile)
-               err = ovl_do_link(temp, udir, upper);
-       else
-               err = ovl_do_rename(d_inode(c->workdir), temp, udir, upper, 0);
-
-       if (!err)
-               *newdentry = dget(c->tmpfile ? upper : temp);
-       dput(upper);
-
-       return err;
-}
-
-static struct dentry *ovl_get_tmpfile(struct ovl_copy_up_ctx *c)
-{
-       int err;
-       struct dentry *temp;
-       const struct cred *old_creds = NULL;
-       struct cred *new_creds = NULL;
-       struct ovl_cattr cattr = {
-               /* Can't properly set mode on creation because of the umask */
-               .mode = c->stat.mode & S_IFMT,
-               .rdev = c->stat.rdev,
-               .link = c->link
-       };
-
-       err = security_inode_copy_up(c->dentry, &new_creds);
-       if (err < 0)
-               return ERR_PTR(err);
-
-       if (new_creds)
-               old_creds = override_creds(new_creds);
-
-       if (c->tmpfile)
-               temp = ovl_do_tmpfile(c->workdir, c->stat.mode);
-       else
-               temp = ovl_create_temp(c->workdir, &cattr);
-
-       if (new_creds) {
-               revert_creds(old_creds);
-               put_cred(new_creds);
-       }
-
-       return temp;
-}
-
 static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
 {
        int err;
@@ -547,37 +490,94 @@ static int ovl_copy_up_inode(struct ovl_copy_up_ctx *c, struct dentry *temp)
        return err;
 }
 
-static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
+static struct dentry *ovl_get_workdir_temp(struct ovl_copy_up_ctx *c)
+{
+       int err;
+       struct dentry *temp;
+       const struct cred *old_creds = NULL;
+       struct cred *new_creds = NULL;
+       struct ovl_cattr cattr = {
+               /* Can't properly set mode on creation because of the umask */
+               .mode = c->stat.mode & S_IFMT,
+               .rdev = c->stat.rdev,
+               .link = c->link
+       };
+
+       err = security_inode_copy_up(c->dentry, &new_creds);
+       if (err < 0)
+               return ERR_PTR(err);
+
+       if (new_creds)
+               old_creds = override_creds(new_creds);
+
+       temp = ovl_create_temp(c->workdir, &cattr);
+
+       if (new_creds) {
+               revert_creds(old_creds);
+               put_cred(new_creds);
+       }
+
+       return temp;
+}
+
+/*
+ * Move temp file from workdir into place on upper dir.
+ * Used when copying up directories and when upper fs doesn't support O_TMPFILE.
+ *
+ * Caller must hold ovl_lock_rename_workdir().
+ */
+static int ovl_rename_temp(struct ovl_copy_up_ctx *c, struct dentry *temp,
+                          struct dentry **newdentry)
+{
+       int err;
+       struct dentry *upper;
+       struct inode *udir = d_inode(c->destdir);
+
+       upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
+       if (IS_ERR(upper))
+               return PTR_ERR(upper);
+
+       err = ovl_do_rename(d_inode(c->workdir), temp, udir, upper, 0);
+       if (!err)
+               *newdentry = dget(temp);
+       dput(upper);
+
+       return err;
+}
+
+/*
+ * Copyup using workdir to prepare temp file.  Used when copying up directories,
+ * special files or when upper fs doesn't support O_TMPFILE.
+ */
+static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
 {
-       struct inode *udir = c->destdir->d_inode;
        struct inode *inode;
        struct dentry *newdentry = NULL;
        struct dentry *temp;
        int err;
 
-       temp = ovl_get_tmpfile(c);
+       err = ovl_lock_rename_workdir(c->workdir, c->destdir);
+       if (err)
+               return err;
+
+       temp = ovl_get_workdir_temp(c);
+       err = PTR_ERR(temp);
        if (IS_ERR(temp))
-               return PTR_ERR(temp);
+               goto unlock;
 
        err = ovl_copy_up_inode(c, temp);
        if (err)
-               goto out;
+               goto cleanup;
 
        if (S_ISDIR(c->stat.mode) && c->indexed) {
                err = ovl_create_index(c->dentry, c->lowerpath.dentry, temp);
                if (err)
-                       goto out;
+                       goto cleanup;
        }
 
-       if (c->tmpfile) {
-               inode_lock_nested(udir, I_MUTEX_PARENT);
-               err = ovl_install_temp(c, temp, &newdentry);
-               inode_unlock(udir);
-       } else {
-               err = ovl_install_temp(c, temp, &newdentry);
-       }
+       err = ovl_rename_temp(c, temp, &newdentry);
        if (err)
-               goto out;
+               goto cleanup;
 
        if (!c->metacopy)
                ovl_set_upperdata(d_inode(c->dentry));
@@ -585,13 +585,94 @@ static int ovl_copy_up_locked(struct ovl_copy_up_ctx *c)
        ovl_inode_update(inode, newdentry);
        if (S_ISDIR(inode->i_mode))
                ovl_set_flag(OVL_WHITEOUTS, inode);
+out_dput:
+       dput(temp);
+unlock:
+       unlock_rename(c->workdir, c->destdir);
+
+       return err;
+
+cleanup:
+       ovl_cleanup(d_inode(c->workdir), temp);
+       goto out_dput;
+}
+
+static struct dentry *ovl_get_tmpfile(struct ovl_copy_up_ctx *c)
+{
+       int err;
+       struct dentry *temp;
+       const struct cred *old_creds = NULL;
+       struct cred *new_creds = NULL;
+
+       err = security_inode_copy_up(c->dentry, &new_creds);
+       if (err < 0)
+               return ERR_PTR(err);
+
+       if (new_creds)
+               old_creds = override_creds(new_creds);
+
+       temp = ovl_do_tmpfile(c->workdir, c->stat.mode);
+
+       if (new_creds) {
+               revert_creds(old_creds);
+               put_cred(new_creds);
+       }
+
+       return temp;
+}
+
+/* Link O_TMPFILE into place on upper dir */
+static int ovl_link_tmpfile(struct ovl_copy_up_ctx *c, struct dentry *temp,
+                           struct dentry **newdentry)
+{
+       int err;
+       struct dentry *upper;
+       struct inode *udir = d_inode(c->destdir);
+
+       inode_lock_nested(udir, I_MUTEX_PARENT);
+
+       upper = lookup_one_len(c->destname.name, c->destdir, c->destname.len);
+       err = PTR_ERR(upper);
+       if (IS_ERR(upper))
+               goto unlock;
+
+       err = ovl_do_link(temp, udir, upper);
+       if (!err)
+               *newdentry = dget(upper);
+       dput(upper);
+
+unlock:
+       inode_unlock(udir);
+
+       return err;
+}
+
+/* Copyup using O_TMPFILE which does not require cross dir locking */
+static int ovl_copy_up_tmpfile(struct ovl_copy_up_ctx *c)
+{
+       struct dentry *newdentry = NULL;
+       struct dentry *temp;
+       int err;
+
+       temp = ovl_get_tmpfile(c);
+       if (IS_ERR(temp))
+               return PTR_ERR(temp);
+
+       err = ovl_copy_up_inode(c, temp);
+       if (err)
+               goto out;
+
+       err = ovl_link_tmpfile(c, temp, &newdentry);
+       if (err)
+               goto out;
+
+       if (!c->metacopy)
+               ovl_set_upperdata(d_inode(c->dentry));
+       ovl_inode_update(d_inode(c->dentry), newdentry);
 
 out:
-       if (err && !c->tmpfile)
-               ovl_cleanup(d_inode(c->workdir), temp);
        dput(temp);
        return err;
-
 }
 
 /*
@@ -645,18 +726,10 @@ static int ovl_do_copy_up(struct ovl_copy_up_ctx *c)
        }
 
        /* Should we copyup with O_TMPFILE or with workdir? */
-       if (S_ISREG(c->stat.mode) && ofs->tmpfile) {
-               c->tmpfile = true;
-               err = ovl_copy_up_locked(c);
-       } else {
-               err = ovl_lock_rename_workdir(c->workdir, c->destdir);
-               if (!err) {
-                       err = ovl_copy_up_locked(c);
-                       unlock_rename(c->workdir, c->destdir);
-               }
-       }
-
-
+       if (S_ISREG(c->stat.mode) && ofs->tmpfile)
+               err = ovl_copy_up_tmpfile(c);
+       else
+               err = ovl_copy_up_workdir(c);
        if (err)
                goto out;