diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt index eef7d9d259e8..f20589841d2e 100644 --- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -102,6 +102,29 @@ Only the lists of names from directories are merged. Other content such as metadata and extended attributes are reported for the upper directory only. These attributes of the lower directory are hidden. +credentials +----------- + +By default, all access to the upper, lower and work directories is the +recorded mounter's MAC and DAC credentials. The incoming accesses are +checked against the caller's credentials. + +In the case where caller MAC or DAC credentials do not overlap, a +use case available in older versions of the driver, the +override_creds mount flag can be turned off and help when the use +pattern has caller with legitimate credentials where the mounter +does not. Several unintended side effects will occur though. The +caller without certain key capabilities or lower privilege will not +always be able to delete files or directories, create nodes, or +search some restricted directories. The ability to search and read +a directory entry is spotty as a result of the cache mechanism not +retesting the credentials because of the assumption, a privileged +caller can fill cache, then a lower privilege can read the directory +cache. The uneven security model where cache, upperdir and workdir +are opened at privilege, but accessed without creating a form of +privilege escalation, should only be used with strict understanding +of the side effects and of the security policies. + whiteouts and opaque directories -------------------------------- diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c index 1cc797a08a5b..e6b5d6216302 100644 --- a/fs/overlayfs/copy_up.c +++ b/fs/overlayfs/copy_up.c @@ -829,7 +829,7 @@ int ovl_copy_up_flags(struct dentry *dentry, int flags) dput(parent); dput(next); } - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c index b2aadd3e1fec..2e4af5f46195 100644 --- a/fs/overlayfs/dir.c +++ b/fs/overlayfs/dir.c @@ -567,7 +567,8 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode, override_cred->fsgid = inode->i_gid; if (!attr->hardlink) { err = security_dentry_create_files_as(dentry, - attr->mode, &dentry->d_name, old_cred, + attr->mode, &dentry->d_name, + old_cred ? old_cred : current_cred(), override_cred); if (err) { put_cred(override_cred); @@ -583,7 +584,7 @@ static int ovl_create_or_link(struct dentry *dentry, struct inode *inode, err = ovl_create_over_whiteout(dentry, inode, attr); } out_revert_creds: - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } @@ -659,7 +660,7 @@ static int ovl_set_link_redirect(struct dentry *dentry) old_cred = ovl_override_creds(dentry->d_sb); err = ovl_set_redirect(dentry, false); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } @@ -857,7 +858,7 @@ static int ovl_do_remove(struct dentry *dentry, bool is_dir) err = ovl_remove_upper(dentry, is_dir, &list); else err = ovl_remove_and_whiteout(dentry, &list); - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (!err) { if (is_dir) clear_nlink(dentry->d_inode); @@ -1225,7 +1226,7 @@ static int ovl_rename(struct inode *olddir, struct dentry *old, out_unlock: unlock_rename(new_upperdir, old_upperdir); out_revert_creds: - revert_creds(old_cred); + ovl_revert_creds(old_cred); ovl_nlink_end(new, locked); out_drop_write: ovl_drop_write(old); diff --git a/fs/overlayfs/file.c b/fs/overlayfs/file.c index 986313da0c88..da7d7856fcda 100644 --- a/fs/overlayfs/file.c +++ b/fs/overlayfs/file.c @@ -33,7 +33,7 @@ static struct file *ovl_open_realfile(const struct file *file, old_cred = ovl_override_creds(inode->i_sb); realfile = open_with_fake_path(&file->f_path, file->f_flags | O_NOATIME, realinode, current_cred()); - revert_creds(old_cred); + ovl_revert_creds(old_cred); pr_debug("open(%p[%pD2/%c], 0%o) -> (%p, 0%o)\n", file, file, ovl_whatisit(inode, realinode), file->f_flags, @@ -208,7 +208,7 @@ static ssize_t ovl_read_iter(struct kiocb *iocb, struct iov_iter *iter) old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_iter_read(real.file, iter, &iocb->ki_pos, ovl_iocb_to_rwf(iocb)); - revert_creds(old_cred); + ovl_revert_creds(old_cred); ovl_file_accessed(file); @@ -244,7 +244,7 @@ static ssize_t ovl_write_iter(struct kiocb *iocb, struct iov_iter *iter) ret = vfs_iter_write(real.file, iter, &iocb->ki_pos, ovl_iocb_to_rwf(iocb)); file_end_write(real.file); - revert_creds(old_cred); + ovl_revert_creds(old_cred); /* Update size */ ovl_copyattr(ovl_inode_real(inode), inode); @@ -271,7 +271,7 @@ static int ovl_fsync(struct file *file, loff_t start, loff_t end, int datasync) if (file_inode(real.file) == ovl_inode_upper(file_inode(file))) { old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_fsync_range(real.file, start, end, datasync); - revert_creds(old_cred); + ovl_revert_creds(old_cred); } fdput(real); @@ -295,7 +295,7 @@ static int ovl_mmap(struct file *file, struct vm_area_struct *vma) old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = call_mmap(vma->vm_file, vma); - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (ret) { /* Drop reference count from new vm_file value */ @@ -323,7 +323,7 @@ static long ovl_fallocate(struct file *file, int mode, loff_t offset, loff_t len old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_fallocate(real.file, mode, offset, len); - revert_creds(old_cred); + ovl_revert_creds(old_cred); /* Update size */ ovl_copyattr(ovl_inode_real(inode), inode); @@ -345,7 +345,7 @@ static int ovl_fadvise(struct file *file, loff_t offset, loff_t len, int advice) old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_fadvise(real.file, offset, len, advice); - revert_creds(old_cred); + ovl_revert_creds(old_cred); fdput(real); @@ -365,7 +365,7 @@ static long ovl_real_ioctl(struct file *file, unsigned int cmd, old_cred = ovl_override_creds(file_inode(file)->i_sb); ret = vfs_ioctl(real.file, cmd, arg); - revert_creds(old_cred); + ovl_revert_creds(old_cred); fdput(real); @@ -470,7 +470,7 @@ static ssize_t ovl_copyfile(struct file *file_in, loff_t pos_in, real_out.file, pos_out, len); break; } - revert_creds(old_cred); + ovl_revert_creds(old_cred); /* Update size */ ovl_copyattr(ovl_inode_real(inode_out), inode_out); diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c index 3b7ed5d2279c..b3c61267c8b5 100644 --- a/fs/overlayfs/inode.c +++ b/fs/overlayfs/inode.c @@ -64,7 +64,7 @@ int ovl_setattr(struct dentry *dentry, struct iattr *attr) inode_lock(upperdentry->d_inode); old_cred = ovl_override_creds(dentry->d_sb); err = notify_change(upperdentry, attr, NULL); - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (!err) ovl_copyattr(upperdentry->d_inode, dentry->d_inode); inode_unlock(upperdentry->d_inode); @@ -260,7 +260,7 @@ int ovl_getattr(const struct path *path, struct kstat *stat, stat->nlink = dentry->d_inode->i_nlink; out: - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } @@ -294,7 +294,7 @@ int ovl_permission(struct inode *inode, int mask) mask |= MAY_READ; } err = inode_permission(realinode, mask); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } @@ -311,7 +311,7 @@ static const char *ovl_get_link(struct dentry *dentry, old_cred = ovl_override_creds(dentry->d_sb); p = vfs_get_link(ovl_dentry_real(dentry), done); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return p; } @@ -354,7 +354,7 @@ int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name, WARN_ON(flags != XATTR_REPLACE); err = vfs_removexattr(realdentry, name); } - revert_creds(old_cred); + ovl_revert_creds(old_cred); /* copy c/mtime */ ovl_copyattr(d_inode(realdentry), inode); @@ -375,7 +375,7 @@ int ovl_xattr_get(struct dentry *dentry, struct inode *inode, const char *name, old_cred = ovl_override_creds(dentry->d_sb); res = vfs_getxattr(realdentry, name, value, size); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return res; } @@ -399,7 +399,7 @@ ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size) old_cred = ovl_override_creds(dentry->d_sb); res = vfs_listxattr(realdentry, list, size); - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (res <= 0 || size == 0) return res; @@ -434,7 +434,7 @@ struct posix_acl *ovl_get_acl(struct inode *inode, int type) old_cred = ovl_override_creds(inode->i_sb); acl = get_acl(realinode, type); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return acl; } @@ -472,7 +472,7 @@ static int ovl_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo, filemap_write_and_wait(realinode->i_mapping); err = realinode->i_op->fiemap(realinode, fieinfo, start, len); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } diff --git a/fs/overlayfs/namei.c b/fs/overlayfs/namei.c index efd372312ef1..2fd199e9be97 100644 --- a/fs/overlayfs/namei.c +++ b/fs/overlayfs/namei.c @@ -1069,7 +1069,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, goto out_free_oe; } - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (origin_path) { dput(origin_path->dentry); kfree(origin_path); @@ -1096,7 +1096,7 @@ struct dentry *ovl_lookup(struct inode *dir, struct dentry *dentry, kfree(upperredirect); out: kfree(d.redirect); - revert_creds(old_cred); + ovl_revert_creds(old_cred); return ERR_PTR(err); } @@ -1150,7 +1150,7 @@ bool ovl_lower_positive(struct dentry *dentry) dput(this); } } - revert_creds(old_cred); + ovl_revert_creds(old_cred); return positive; } diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h index a3c0d9584312..552a19abc155 100644 --- a/fs/overlayfs/overlayfs.h +++ b/fs/overlayfs/overlayfs.h @@ -208,6 +208,7 @@ int ovl_want_write(struct dentry *dentry); void ovl_drop_write(struct dentry *dentry); struct dentry *ovl_workdir(struct dentry *dentry); const struct cred *ovl_override_creds(struct super_block *sb); +void ovl_revert_creds(const struct cred *oldcred); struct super_block *ovl_same_sb(struct super_block *sb); int ovl_can_decode_fh(struct super_block *sb); struct dentry *ovl_indexdir(struct super_block *sb); diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h index ec237035333a..e38eea8104be 100644 --- a/fs/overlayfs/ovl_entry.h +++ b/fs/overlayfs/ovl_entry.h @@ -20,6 +20,7 @@ struct ovl_config { bool nfs_export; int xino; bool metacopy; + bool override_creds; }; struct ovl_sb { diff --git a/fs/overlayfs/readdir.c b/fs/overlayfs/readdir.c index cc8303a806b4..ec591b49e902 100644 --- a/fs/overlayfs/readdir.c +++ b/fs/overlayfs/readdir.c @@ -289,7 +289,7 @@ static int ovl_check_whiteouts(struct dentry *dir, struct ovl_readdir_data *rdd) } inode_unlock(dir->d_inode); } - revert_creds(old_cred); + ovl_revert_creds(old_cred); return err; } @@ -921,7 +921,7 @@ int ovl_check_empty_dir(struct dentry *dentry, struct list_head *list) old_cred = ovl_override_creds(dentry->d_sb); err = ovl_dir_read_merged(dentry, list, &root); - revert_creds(old_cred); + ovl_revert_creds(old_cred); if (err) return err; diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c index 0fb0a59a5e5c..df7706218987 100644 --- a/fs/overlayfs/super.c +++ b/fs/overlayfs/super.c @@ -56,6 +56,11 @@ module_param_named(xino_auto, ovl_xino_auto_def, bool, 0644); MODULE_PARM_DESC(ovl_xino_auto_def, "Auto enable xino feature"); +static bool __read_mostly ovl_override_creds_def = true; +module_param_named(override_creds, ovl_override_creds_def, bool, 0644); +MODULE_PARM_DESC(ovl_override_creds_def, + "Use mounter's credentials for accesses"); + static void ovl_entry_stack_free(struct ovl_entry *oe) { unsigned int i; @@ -362,6 +367,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry) if (ofs->config.metacopy != ovl_metacopy_def) seq_printf(m, ",metacopy=%s", ofs->config.metacopy ? "on" : "off"); + if (ofs->config.override_creds != ovl_override_creds_def) + seq_show_option(m, "override_creds", + ofs->config.override_creds ? "on" : "off"); return 0; } @@ -401,6 +409,8 @@ enum { OPT_XINO_AUTO, OPT_METACOPY_ON, OPT_METACOPY_OFF, + OPT_OVERRIDE_CREDS_ON, + OPT_OVERRIDE_CREDS_OFF, OPT_ERR, }; @@ -419,6 +429,8 @@ static const match_table_t ovl_tokens = { {OPT_XINO_AUTO, "xino=auto"}, {OPT_METACOPY_ON, "metacopy=on"}, {OPT_METACOPY_OFF, "metacopy=off"}, + {OPT_OVERRIDE_CREDS_ON, "override_creds=on"}, + {OPT_OVERRIDE_CREDS_OFF, "override_creds=off"}, {OPT_ERR, NULL} }; @@ -477,6 +489,7 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config) config->redirect_mode = kstrdup(ovl_redirect_mode_def(), GFP_KERNEL); if (!config->redirect_mode) return -ENOMEM; + config->override_creds = ovl_override_creds_def; while ((p = ovl_next_opt(&opt)) != NULL) { int token; @@ -557,6 +570,14 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config) config->metacopy = false; break; + case OPT_OVERRIDE_CREDS_ON: + config->override_creds = true; + break; + + case OPT_OVERRIDE_CREDS_OFF: + config->override_creds = false; + break; + default: pr_err("overlayfs: unrecognized mount option \"%s\" or missing value\n", p); return -EINVAL; @@ -1521,7 +1542,6 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent) ovl_dentry_lower(root_dentry), NULL); sb->s_root = root_dentry; - return 0; out_free_oe: diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c index ace4fe4c39a9..470310e68558 100644 --- a/fs/overlayfs/util.c +++ b/fs/overlayfs/util.c @@ -40,9 +40,17 @@ const struct cred *ovl_override_creds(struct super_block *sb) { struct ovl_fs *ofs = sb->s_fs_info; + if (!ofs->config.override_creds) + return NULL; return override_creds(ofs->creator_cred); } +void ovl_revert_creds(const struct cred *old_cred) +{ + if (old_cred) + revert_creds(old_cred); +} + struct super_block *ovl_same_sb(struct super_block *sb) { struct ovl_fs *ofs = sb->s_fs_info; @@ -783,7 +791,7 @@ int ovl_nlink_start(struct dentry *dentry, bool *locked) * value relative to the upper inode nlink in an upper inode xattr. */ err = ovl_set_nlink_upper(dentry); - revert_creds(old_cred); + ovl_revert_creds(old_cred); out: if (err) @@ -803,7 +811,7 @@ void ovl_nlink_end(struct dentry *dentry, bool locked) old_cred = ovl_override_creds(dentry->d_sb); ovl_cleanup_index(dentry); - revert_creds(old_cred); + ovl_revert_creds(old_cred); } mutex_unlock(&OVL_I(d_inode(dentry))->lock);