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From: Miklos Szeredi <mszeredi@redhat.com>
To: "Eric W . Biederman" <ebiederm@xmission.com>
Cc: linux-fsdevel@vger.kernel.org, linux-unionfs@vger.kernel.org,
	linux-security-module@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: [PATCH v2 06/10] ovl: user xattr
Date: Mon,  7 Dec 2020 17:32:51 +0100	[thread overview]
Message-ID: <20201207163255.564116-7-mszeredi@redhat.com> (raw)
In-Reply-To: <20201207163255.564116-1-mszeredi@redhat.com>

Optionally allow using "user.overlay." namespace instead of
"trusted.overlay."

This is necessary for overlayfs to be able to be mounted in an unprivileged
namepsace.

Make the option explicit, since it makes the filesystem format be
incompatible.

Disable redirect_dir and metacopy options, because these would allow
privilege escalation through direct manipulation of the
"user.overlay.redirect" or "user.overlay.metacopy" xattrs.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
---
 fs/overlayfs/inode.c     | 10 ++++++--
 fs/overlayfs/overlayfs.h |  8 +++---
 fs/overlayfs/ovl_entry.h |  1 +
 fs/overlayfs/super.c     | 55 ++++++++++++++++++++++++++++++++++++----
 fs/overlayfs/util.c      |  5 ++--
 5 files changed, 67 insertions(+), 12 deletions(-)

diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
index b584dca845ba..8ec3062999a9 100644
--- a/fs/overlayfs/inode.c
+++ b/fs/overlayfs/inode.c
@@ -329,8 +329,14 @@ static const char *ovl_get_link(struct dentry *dentry,
 
 bool ovl_is_private_xattr(struct super_block *sb, const char *name)
 {
-	return strncmp(name, OVL_XATTR_PREFIX,
-		       sizeof(OVL_XATTR_PREFIX) - 1) == 0;
+	struct ovl_fs *ofs = sb->s_fs_info;
+
+	if (ofs->config.userxattr)
+		return strncmp(name, OVL_XATTR_USER_PREFIX,
+			       sizeof(OVL_XATTR_USER_PREFIX) - 1) == 0;
+	else
+		return strncmp(name, OVL_XATTR_TRUSTED_PREFIX,
+			       sizeof(OVL_XATTR_TRUSTED_PREFIX) - 1) == 0;
 }
 
 int ovl_xattr_set(struct dentry *dentry, struct inode *inode, const char *name,
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index f8880aa2ba0e..46282111d6e6 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -22,7 +22,9 @@ enum ovl_path_type {
 #define OVL_TYPE_MERGE(type)	((type) & __OVL_PATH_MERGE)
 #define OVL_TYPE_ORIGIN(type)	((type) & __OVL_PATH_ORIGIN)
 
-#define OVL_XATTR_PREFIX XATTR_TRUSTED_PREFIX "overlay."
+#define OVL_XATTR_NAMESPACE "overlay."
+#define OVL_XATTR_TRUSTED_PREFIX XATTR_TRUSTED_PREFIX OVL_XATTR_NAMESPACE
+#define OVL_XATTR_USER_PREFIX XATTR_USER_PREFIX OVL_XATTR_NAMESPACE
 
 enum ovl_xattr {
 	OVL_XATTR_OPAQUE,
@@ -113,10 +115,10 @@ struct ovl_fh {
 #define OVL_FH_FID_OFFSET	(OVL_FH_WIRE_OFFSET + \
 				 offsetof(struct ovl_fb, fid))
 
-extern const char *ovl_xattr_table[];
+extern const char *ovl_xattr_table[][2];
 static inline const char *ovl_xattr(struct ovl_fs *ofs, enum ovl_xattr ox)
 {
-	return ovl_xattr_table[ox];
+	return ovl_xattr_table[ox][ofs->config.userxattr];
 }
 
 static inline int ovl_do_rmdir(struct inode *dir, struct dentry *dentry)
diff --git a/fs/overlayfs/ovl_entry.h b/fs/overlayfs/ovl_entry.h
index 1b5a2094df8e..d634c7ba3b9c 100644
--- a/fs/overlayfs/ovl_entry.h
+++ b/fs/overlayfs/ovl_entry.h
@@ -17,6 +17,7 @@ struct ovl_config {
 	bool nfs_export;
 	int xino;
 	bool metacopy;
+	bool userxattr;
 	bool ovl_volatile;
 };
 
diff --git a/fs/overlayfs/super.c b/fs/overlayfs/super.c
index 290983bcfbb3..189380b946be 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -411,6 +411,7 @@ enum {
 	OPT_INDEX_ON,
 	OPT_INDEX_OFF,
 	OPT_NFS_EXPORT_ON,
+	OPT_USERXATTR,
 	OPT_NFS_EXPORT_OFF,
 	OPT_XINO_ON,
 	OPT_XINO_OFF,
@@ -429,6 +430,7 @@ static const match_table_t ovl_tokens = {
 	{OPT_REDIRECT_DIR,		"redirect_dir=%s"},
 	{OPT_INDEX_ON,			"index=on"},
 	{OPT_INDEX_OFF,			"index=off"},
+	{OPT_USERXATTR,			"userxattr"},
 	{OPT_NFS_EXPORT_ON,		"nfs_export=on"},
 	{OPT_NFS_EXPORT_OFF,		"nfs_export=off"},
 	{OPT_XINO_ON,			"xino=on"},
@@ -585,6 +587,10 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 			config->ovl_volatile = true;
 			break;
 
+		case OPT_USERXATTR:
+			config->userxattr = true;
+			break;
+
 		default:
 			pr_err("unrecognized mount option \"%s\" or missing value\n",
 					p);
@@ -688,6 +694,28 @@ static int ovl_parse_opt(char *opt, struct ovl_config *config)
 		}
 	}
 
+
+	/* Resolve userxattr -> !redirect && !metacopy dependency */
+	if (config->userxattr) {
+		if (config->redirect_follow && redirect_opt) {
+			pr_err("conflicting options: userxattr,redirect_dir=%s\n",
+			       config->redirect_mode);
+			return -EINVAL;
+		}
+		if (config->metacopy && metacopy_opt) {
+			pr_err("conflicting options: userxattr,metacopy=on\n");
+			return -EINVAL;
+		}
+		/*
+		 * Silently disable default setting of redirect and metacopy.
+		 * This shall be the default in the future as well: these
+		 * options must be explicitly enabled if used together with
+		 * userxattr.
+		 */
+		config->redirect_dir = config->redirect_follow = false;
+		config->metacopy = false;
+	}
+
 	return 0;
 }
 
@@ -1037,8 +1065,14 @@ ovl_posix_acl_default_xattr_handler = {
 	.set = ovl_posix_acl_xattr_set,
 };
 
-static const struct xattr_handler ovl_own_xattr_handler = {
-	.prefix	= OVL_XATTR_PREFIX,
+static const struct xattr_handler ovl_own_trusted_xattr_handler = {
+	.prefix	= OVL_XATTR_TRUSTED_PREFIX,
+	.get = ovl_own_xattr_get,
+	.set = ovl_own_xattr_set,
+};
+
+static const struct xattr_handler ovl_own_user_xattr_handler = {
+	.prefix	= OVL_XATTR_USER_PREFIX,
 	.get = ovl_own_xattr_get,
 	.set = ovl_own_xattr_set,
 };
@@ -1049,12 +1083,22 @@ static const struct xattr_handler ovl_other_xattr_handler = {
 	.set = ovl_other_xattr_set,
 };
 
-static const struct xattr_handler *ovl_xattr_handlers[] = {
+static const struct xattr_handler *ovl_trusted_xattr_handlers[] = {
+#ifdef CONFIG_FS_POSIX_ACL
+	&ovl_posix_acl_access_xattr_handler,
+	&ovl_posix_acl_default_xattr_handler,
+#endif
+	&ovl_own_trusted_xattr_handler,
+	&ovl_other_xattr_handler,
+	NULL
+};
+
+static const struct xattr_handler *ovl_user_xattr_handlers[] = {
 #ifdef CONFIG_FS_POSIX_ACL
 	&ovl_posix_acl_access_xattr_handler,
 	&ovl_posix_acl_default_xattr_handler,
 #endif
-	&ovl_own_xattr_handler,
+	&ovl_own_user_xattr_handler,
 	&ovl_other_xattr_handler,
 	NULL
 };
@@ -1991,7 +2035,8 @@ static int ovl_fill_super(struct super_block *sb, void *data, int silent)
 	cap_lower(cred->cap_effective, CAP_SYS_RESOURCE);
 
 	sb->s_magic = OVERLAYFS_SUPER_MAGIC;
-	sb->s_xattr = ovl_xattr_handlers;
+	sb->s_xattr = ofs->config.userxattr ? ovl_user_xattr_handlers :
+		ovl_trusted_xattr_handlers;
 	sb->s_fs_info = ofs;
 	sb->s_flags |= SB_POSIXACL;
 	sb->s_iflags |= SB_I_SKIP_SYNC;
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 23f475627d07..66eaf4db027f 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -582,9 +582,10 @@ bool ovl_check_dir_xattr(struct super_block *sb, struct dentry *dentry,
 #define OVL_XATTR_METACOPY_POSTFIX	"metacopy"
 
 #define OVL_XATTR_TAB_ENTRY(x) \
-	[x] = OVL_XATTR_PREFIX x ## _POSTFIX
+	[x] = { [false] = OVL_XATTR_TRUSTED_PREFIX x ## _POSTFIX, \
+		[true] = OVL_XATTR_USER_PREFIX x ## _POSTFIX }
 
-const char *ovl_xattr_table[] = {
+const char *ovl_xattr_table[][2] = {
 	OVL_XATTR_TAB_ENTRY(OVL_XATTR_OPAQUE),
 	OVL_XATTR_TAB_ENTRY(OVL_XATTR_REDIRECT),
 	OVL_XATTR_TAB_ENTRY(OVL_XATTR_ORIGIN),
-- 
2.26.2


  parent reply	other threads:[~2020-12-07 16:35 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-07 16:32 [PATCH v2 00/10] allow unprivileged overlay mounts Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 01/10] vfs: move cap_convert_nscap() call into vfs_setxattr() Miklos Szeredi
2020-12-09  1:53   ` James Morris
2021-01-01 17:35   ` Eric W. Biederman
2021-01-11 13:49     ` Miklos Szeredi
2021-01-12  0:14       ` Eric W. Biederman
2021-01-12  9:43         ` Miklos Szeredi
2021-01-12 10:04           ` Miklos Szeredi
2021-01-12 18:36           ` Eric W. Biederman
2021-01-12 18:49             ` Eric W. Biederman
2020-12-07 16:32 ` [PATCH v2 02/10] vfs: verify source area in vfs_dedupe_file_range_one() Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 03/10] ovl: check privs before decoding file handle Miklos Szeredi
2020-12-08 13:49   ` Amir Goldstein
2020-12-09 10:13     ` Miklos Szeredi
2020-12-09 16:20       ` Miklos Szeredi
2020-12-09 18:16         ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 04/10] ovl: make ioctl() safe Miklos Szeredi
2020-12-08 11:11   ` Amir Goldstein
2020-12-10 15:18     ` Miklos Szeredi
2020-12-14  5:44       ` Amir Goldstein
2020-12-14 13:23         ` Miklos Szeredi
2020-12-14 14:47           ` Amir Goldstein
2020-12-09  1:57   ` James Morris
2020-12-10 15:19     ` Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 05/10] ovl: simplify file splice Miklos Szeredi
2020-12-07 16:32 ` Miklos Szeredi [this message]
2020-12-08 13:10   ` [PATCH v2 06/10] ovl: user xattr Amir Goldstein
2020-12-11 14:55     ` Miklos Szeredi
2020-12-14  5:13       ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 07/10] ovl: do not fail when setting origin xattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 08/10] ovl: do not fail because of O_NOATIME Miklos Szeredi
2020-12-08 11:29   ` Amir Goldstein
2020-12-11 14:44     ` Miklos Szeredi
2020-12-14  5:49       ` Amir Goldstein
2020-12-07 16:32 ` [PATCH v2 09/10] ovl: do not get metacopy for userxattr Miklos Szeredi
2020-12-07 16:32 ` [PATCH v2 10/10] ovl: unprivieged mounts Miklos Szeredi
2020-12-08 10:27 ` [PATCH v2 00/10] allow unprivileged overlay mounts Tetsuo Handa
2020-12-10  8:56   ` John Johansen
2020-12-10  9:39     ` Miklos Szeredi
2020-12-15 11:03       ` John Johansen

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