Merge branch 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs

Pull overlayfs update from Miklos Szeredi:
 "The meat of this is a change to use the mounter's credentials for
  operations that require elevated privileges (such as whiteout
  creation).  This fixes behavior under user namespaces as well as being
  a nice cleanup"

* 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs:
  ovl: Do d_type check only if work dir creation was successful
  ovl: update documentation
  ovl: override creds with the ones from the superblock mounter

6 files changed, 38 insertions, 116 deletions

diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt
index 28091457b71a..d6259c786316 100644
--- a/Documentation/filesystems/overlayfs.txt
+++ b/Documentation/filesystems/overlayfs.txt
@@ -194,15 +194,6 @@ If a file with multiple hard links is copied up, then this will
 "break" the link.  Changes will not be propagated to other names
 referring to the same inode.
 
-Symlinks in /proc/PID/ and /proc/PID/fd which point to a non-directory
-object in overlayfs will not contain valid absolute paths, only
-relative paths leading up to the filesystem's root.  This will be
-fixed in the future.
-
-Some operations are not atomic, for example a crash during copy_up or
-rename will leave the filesystem in an inconsistent state.  This will
-be addressed in the future.
-
 Changes to underlying filesystems
 ---------------------------------
 
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index cc514da6f3e7..80aa6f1eb336 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -336,7 +336,6 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
         struct dentry *upperdir;
         struct dentry *upperdentry;
         const struct cred *old_cred;
-        struct cred *override_cred;
         char *link = NULL;
 
         if (WARN_ON(!workdir))
@@ -357,28 +356,7 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
                         return PTR_ERR(link);
         }
 
-        err = -ENOMEM;
-        override_cred = prepare_creds();
-        if (!override_cred)
-                goto out_free_link;
-
-        override_cred->fsuid = stat->uid;
-        override_cred->fsgid = stat->gid;
-        /*
-         * CAP_SYS_ADMIN for copying up extended attributes
-         * CAP_DAC_OVERRIDE for create
-         * CAP_FOWNER for chmod, timestamp update
-         * CAP_FSETID for chmod
-         * CAP_CHOWN for chown
-         * CAP_MKNOD for mknod
-         */
-        cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
-        cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-        cap_raise(override_cred->cap_effective, CAP_FOWNER);
-        cap_raise(override_cred->cap_effective, CAP_FSETID);
-        cap_raise(override_cred->cap_effective, CAP_CHOWN);
-        cap_raise(override_cred->cap_effective, CAP_MKNOD);
-        old_cred = override_creds(override_cred);
+        old_cred = ovl_override_creds(dentry->d_sb);
 
         err = -EIO;
         if (lock_rename(workdir, upperdir) != NULL) {
@@ -401,9 +379,7 @@ int ovl_copy_up_one(struct dentry *parent, struct dentry *dentry,
 out_unlock:
         unlock_rename(workdir, upperdir);
         revert_creds(old_cred);
-        put_cred(override_cred);
 
-out_free_link:
         if (link)
                 free_page((unsigned long) link);
 
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index b3fc0a35bf62..22f0253a3567 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -405,28 +405,13 @@ static int ovl_create_or_link(struct dentry *dentry, int mode, dev_t rdev,
                 err = ovl_create_upper(dentry, inode, &stat, link, hardlink);
         } else {
                 const struct cred *old_cred;
-                struct cred *override_cred;
 
-                err = -ENOMEM;
-                override_cred = prepare_creds();
-                if (!override_cred)
-                        goto out_iput;
-
-                /*
-                 * CAP_SYS_ADMIN for setting opaque xattr
-                 * CAP_DAC_OVERRIDE for create in workdir, rename
-                 * CAP_FOWNER for removing whiteout from sticky dir
-                 */
-                cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
-                cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-                cap_raise(override_cred->cap_effective, CAP_FOWNER);
-                old_cred = override_creds(override_cred);
+                old_cred = ovl_override_creds(dentry->d_sb);
 
                 err = ovl_create_over_whiteout(dentry, inode, &stat, link,
                                                hardlink);
 
                 revert_creds(old_cred);
-                put_cred(override_cred);
         }
 
         if (!err)
@@ -662,32 +647,11 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir)
         if (OVL_TYPE_PURE_UPPER(type)) {
                 err = ovl_remove_upper(dentry, is_dir);
         } else {
-                const struct cred *old_cred;
-                struct cred *override_cred;
-
-                err = -ENOMEM;
-                override_cred = prepare_creds();
-                if (!override_cred)
-                        goto out_drop_write;
-
-                /*
-                 * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir
-                 * CAP_DAC_OVERRIDE for create in workdir, rename
-                 * CAP_FOWNER for removing whiteout from sticky dir
-                 * CAP_FSETID for chmod of opaque dir
-                 * CAP_CHOWN for chown of opaque dir
-                 */
-                cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
-                cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-                cap_raise(override_cred->cap_effective, CAP_FOWNER);
-                cap_raise(override_cred->cap_effective, CAP_FSETID);
-                cap_raise(override_cred->cap_effective, CAP_CHOWN);
-                old_cred = override_creds(override_cred);
+                const struct cred *old_cred = ovl_override_creds(dentry->d_sb);
 
                 err = ovl_remove_and_whiteout(dentry, is_dir);
 
                 revert_creds(old_cred);
-                put_cred(override_cred);
         }
 out_drop_write:
         ovl_drop_write(dentry);
@@ -725,7 +689,6 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
         bool new_is_dir = false;
         struct dentry *opaquedir = NULL;
         const struct cred *old_cred = NULL;
-        struct cred *override_cred = NULL;
 
         err = -EINVAL;
         if (flags & ~(RENAME_EXCHANGE | RENAME_NOREPLACE))
@@ -794,26 +757,8 @@ static int ovl_rename2(struct inode *olddir, struct dentry *old,
         old_opaque = !OVL_TYPE_PURE_UPPER(old_type);
         new_opaque = !OVL_TYPE_PURE_UPPER(new_type);
 
-        if (old_opaque || new_opaque) {
-                err = -ENOMEM;
-                override_cred = prepare_creds();
-                if (!override_cred)
-                        goto out_drop_write;
-
-                /*
-                 * CAP_SYS_ADMIN for setting xattr on whiteout, opaque dir
-                 * CAP_DAC_OVERRIDE for create in workdir
-                 * CAP_FOWNER for removing whiteout from sticky dir
-                 * CAP_FSETID for chmod of opaque dir
-                 * CAP_CHOWN for chown of opaque dir
-                 */
-                cap_raise(override_cred->cap_effective, CAP_SYS_ADMIN);
-                cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-                cap_raise(override_cred->cap_effective, CAP_FOWNER);
-                cap_raise(override_cred->cap_effective, CAP_FSETID);
-                cap_raise(override_cred->cap_effective, CAP_CHOWN);
-                old_cred = override_creds(override_cred);
-        }
+        if (old_opaque || new_opaque)
+                old_cred = ovl_override_creds(old->d_sb);
 
         if (overwrite && OVL_TYPE_MERGE_OR_LOWER(new_type) && new_is_dir) {
                 opaquedir = ovl_check_empty_and_clear(new);
@@ -943,10 +888,8 @@ out_dput_old:
 out_unlock:
         unlock_rename(new_upperdir, old_upperdir);
 out_revert_creds:
-        if (old_opaque || new_opaque) {
+        if (old_opaque || new_opaque)
                 revert_creds(old_cred);
-                put_cred(override_cred);
-        }
 out_drop_write:
         ovl_drop_write(old);
 out:
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 99ec4b035237..724f5fcb4e24 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -153,6 +153,7 @@ void ovl_drop_write(struct dentry *dentry);
 bool ovl_dentry_is_opaque(struct dentry *dentry);
 void ovl_dentry_set_opaque(struct dentry *dentry, bool opaque);
 bool ovl_is_whiteout(struct dentry *dentry);
+const struct cred *ovl_override_creds(struct super_block *sb);
 void ovl_dentry_update(struct dentry *dentry, struct dentry *upperdentry);
 struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry,
                           unsigned int flags);
diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c
index da186ee4f846..d11ae826bcbc 100644
--- a/fs/overlayfs/readdir.c
+++ b/fs/overlayfs/readdir.c
@@ -36,6 +36,7 @@ struct ovl_dir_cache {
 
 struct ovl_readdir_data {
         struct dir_context ctx;
+        struct dentry *dentry;
         bool is_lowest;
         struct rb_root root;
         struct list_head *list;
@@ -206,17 +207,8 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
         struct ovl_cache_entry *p;
         struct dentry *dentry;
         const struct cred *old_cred;
-        struct cred *override_cred;
-
-        override_cred = prepare_creds();
-        if (!override_cred)
-                return -ENOMEM;
 
-        /*
-         * CAP_DAC_OVERRIDE for lookup
-         */
-        cap_raise(override_cred->cap_effective, CAP_DAC_OVERRIDE);
-        old_cred = override_creds(override_cred);
+        old_cred = ovl_override_creds(rdd->dentry->d_sb);
 
         inode_lock(dir->d_inode);
         err = 0;
@@ -234,7 +226,6 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd)
                 inode_unlock(dir->d_inode);
         }
         revert_creds(old_cred);
-        put_cred(override_cred);
 
         return err;
 }
@@ -290,6 +281,7 @@ static int ovl_dir_read_merged(struct dentry *dentry, struct list_head *list)
         struct path realpath;
         struct ovl_readdir_data rdd = {
                 .ctx.actor = ovl_fill_merge,
+                .dentry = dentry,
                 .list = list,
                 .root = RB_ROOT,
                 .is_lowest = false,
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index ed53ae0fe868..ce02f46029da 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -42,6 +42,8 @@ struct ovl_fs {
         long lower_namelen;
         /* pathnames of lower and upper dirs, for show_options */
         struct ovl_config config;
+        /* creds of process who forced instantiation of super block */
+        const struct cred *creator_cred;
 };
 
 struct ovl_dir_cache;
@@ -265,6 +267,13 @@ bool ovl_is_whiteout(struct dentry *dentry)
         return inode && IS_WHITEOUT(inode);
 }
 
+const struct cred *ovl_override_creds(struct super_block *sb)
+{
+        struct ovl_fs *ofs = sb->s_fs_info;
+
+        return override_creds(ofs->creator_cred);
+}
+
 static bool ovl_is_opaquedir(struct dentry *dentry)
 {
         int res;
@@ -603,6 +612,7 @@ static void ovl_put_super(struct super_block *sb)
         kfree(ufs->config.lowerdir);
         kfree(ufs->config.upperdir);
         kfree(ufs->config.workdir);
+        put_cred(ufs->creator_cred);
         kfree(ufs);
 }
 
@@ -1064,16 +1074,19 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
                 /*
                  * Upper should support d_type, else whiteouts are visible.
                  * Given workdir and upper are on same fs, we can do
-                 * iterate_dir() on workdir.
+                 * iterate_dir() on workdir. This check requires successful
+                 * creation of workdir in previous step.
                  */
-                err = ovl_check_d_type_supported(&workpath);
-                if (err < 0)
-                        goto out_put_workdir;
+                if (ufs->workdir) {
+                        err = ovl_check_d_type_supported(&workpath);
+                        if (err < 0)
+                                goto out_put_workdir;
 
-                if (!err) {
-                        pr_err("overlayfs: upper fs needs to support d_type.\n");
-                        err = -EINVAL;
-                        goto out_put_workdir;
+                        if (!err) {
+                                pr_err("overlayfs: upper fs needs to support d_type.\n");
+                                err = -EINVAL;
+                                goto out_put_workdir;
+                        }
                 }
         }
 
@@ -1108,10 +1121,14 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
         else
                 sb->s_d_op = &ovl_dentry_operations;
 
+        ufs->creator_cred = prepare_creds();
+        if (!ufs->creator_cred)
+                goto out_put_lower_mnt;
+
         err = -ENOMEM;
         oe = ovl_alloc_entry(numlower);
         if (!oe)
-                goto out_put_lower_mnt;
+                goto out_put_cred;
 
         root_dentry = d_make_root(ovl_new_inode(sb, S_IFDIR, oe));
         if (!root_dentry)
@@ -1144,6 +1161,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 
 out_free_oe:
         kfree(oe);
+out_put_cred:
+        put_cred(ufs->creator_cred);
 out_put_lower_mnt:
         for (i = 0; i < ufs->numlower; i++)
                 mntput(ufs->lower_mnt[i]);