Patch "fs: create and use seq_show_option for escaping" has been added to the 4.2-stable tree

PATCH [email protected] 1 participant 1 message Sep 19, 2015

Subsystems (12)

Stable branch SELinux security module XFS filesystem ext4 file system +8 more subsystems

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2015-09-19 16:08 UTC #0 lore raw

This is a note to let you know that I've just added the patch titled

fs: create and use seq_show_option for escaping

to the 4.2-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
fs-create-and-use-seq_show_option-for-escaping.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From a068acf2ee77693e0bf39d6e07139ba704f461c3 Mon Sep 17 00:00:00 2001

From: Kees Cook <[email protected]>
Date: Fri, 4 Sep 2015 15:44:57 -0700
Subject: fs: create and use seq_show_option for escaping

From: Kees Cook <[email protected]>

commit a068acf2ee77693e0bf39d6e07139ba704f461c3 upstream.

Many file systems that implement the show_options hook fail to correctly escape their output which could lead to unescaped characters (e.g. new lines) leaking into /proc/mounts and /proc/[pid]/mountinfo files. This could lead to confusion, spoofed entries (resulting in things like systemd issuing false d-bus "mount" notifications), and who knows what else. This looks like it would only be the root user stepping on themselves, but it's possible weird things could happen in containers or in other situations with delegated mount privileges.

Here's an example using overlay with setuid fusermount trusting the contents of /proc/mounts (via the /etc/mtab symlink). Imagine the use of "sudo" is something more sneaky:

  $ BASE="ovl"
  $ MNT="$BASE/mnt"
  $ LOW="$BASE/lower"
  $ UP="$BASE/upper"
  $ WORK="$BASE/work/ 0 0
  none /proc fuse.pwn user_id=1000"
  $ mkdir -p "$LOW" "$UP" "$WORK"
  $ sudo mount -t overlay -o "lowerdir=$LOW,upperdir=$UP,workdir=$WORK" none /mnt
  $ cat /proc/mounts
  none /root/ovl/mnt overlay rw,relatime,lowerdir=ovl/lower,upperdir=ovl/upper,workdir=ovl/work/ 0 0
  none /proc fuse.pwn user_id=1000 0 0
  $ fusermount -u /proc
  $ cat /proc/mounts
  cat: /proc/mounts: No such file or directory

This fixes the problem by adding new seq_show_option and seq_show_option_n helpers, and updating the vulnerable show_option handlers to use them as needed. Some, like SELinux, need to be open coded due to unusual existing escape mechanisms.

[[email protected]: add lost chunk, per Kees]

[[email protected]: seq_show_option should be using const parameters]

Signed-off-by Kees Cook <[email protected]>

Acked-by Serge Hallyn <[email protected]>

Acked-by Jan Kara <[email protected]>

Acked-by Paul Moore <[email protected]>

Cc J. R. Okajima <[email protected]>

Signed-off-by Kees Cook <[email protected]>

Signed-off-by Andrew Morton <[email protected]>

Signed-off-by Linus Torvalds <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 fs/ceph/super.c          |    2 +-
 fs/cifs/cifsfs.c         |    6 +++---
 fs/ext4/super.c          |    4 ++--
 fs/gfs2/super.c          |    6 +++---
 fs/hfs/super.c           |    4 ++--
 fs/hfsplus/options.c     |    4 ++--
 fs/hostfs/hostfs_kern.c  |    2 +-
 fs/ocfs2/super.c         |    4 ++--
 fs/overlayfs/super.c     |    6 +++---
 fs/reiserfs/super.c      |    8 +++++---
 fs/xfs/xfs_super.c       |    4 ++--
 include/linux/seq_file.h |   35 +++++++++++++++++++++++++++++++++++
 kernel/cgroup.c          |    7 ++++---
 net/ceph/ceph_common.c   |    7 +++++--
 security/selinux/hooks.c |    2 +-
 15 files changed, 71 insertions(+), 30 deletions(-)

fs/ceph/super.c +1 -1

@@ -479,7 +479,7 @@ static int ceph_show_options(struct seq_
 	if (fsopt->max_readdir_bytes != CEPH_MAX_READDIR_BYTES_DEFAULT)
 		seq_printf(m, ",readdir_max_bytes=%d", fsopt->max_readdir_bytes);
 	if (strcmp(fsopt->snapdir_name, CEPH_SNAPDIRNAME_DEFAULT))
-		seq_printf(m, ",snapdirname=%s", fsopt->snapdir_name);
+		seq_show_option(m, "snapdirname", fsopt->snapdir_name);
 
 	return 0;
 }

fs/cifs/cifsfs.c +3 -3

@@ -394,17 +394,17 @@ cifs_show_options(struct seq_file *s, st
 	struct sockaddr *srcaddr;
 	srcaddr = (struct sockaddr *)&tcon->ses->server->srcaddr;
 
-	seq_printf(s, ",vers=%s", tcon->ses->server->vals->version_string);
+	seq_show_option(s, "vers", tcon->ses->server->vals->version_string);
 	cifs_show_security(s, tcon->ses);
 	cifs_show_cache_flavor(s, cifs_sb);
 
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MULTIUSER)
 		seq_puts(s, ",multiuser");
 	else if (tcon->ses->user_name)
-		seq_printf(s, ",username=%s", tcon->ses->user_name);
+		seq_show_option(s, "username", tcon->ses->user_name);
 
 	if (tcon->ses->domainName)
-		seq_printf(s, ",domain=%s", tcon->ses->domainName);
+		seq_show_option(s, "domain", tcon->ses->domainName);
 
 	if (srcaddr->sa_family != AF_UNSPEC) {
 		struct sockaddr_in *saddr4;

fs/ext4/super.c +2 -2

@@ -1763,10 +1763,10 @@ static inline void ext4_show_quota_optio
 	}
 
 	if (sbi->s_qf_names[USRQUOTA])
-		seq_printf(seq, ",usrjquota=%s", sbi->s_qf_names[USRQUOTA]);
+		seq_show_option(seq, "usrjquota", sbi->s_qf_names[USRQUOTA]);
 
 	if (sbi->s_qf_names[GRPQUOTA])
-		seq_printf(seq, ",grpjquota=%s", sbi->s_qf_names[GRPQUOTA]);
+		seq_show_option(seq, "grpjquota", sbi->s_qf_names[GRPQUOTA]);
 #endif
 }

fs/gfs2/super.c +3 -3

@@ -1334,11 +1334,11 @@ static int gfs2_show_options(struct seq_
 	if (is_ancestor(root, sdp->sd_master_dir))
 		seq_puts(s, ",meta");
 	if (args->ar_lockproto[0])
-		seq_printf(s, ",lockproto=%s", args->ar_lockproto);
+		seq_show_option(s, "lockproto", args->ar_lockproto);
 	if (args->ar_locktable[0])
-		seq_printf(s, ",locktable=%s", args->ar_locktable);
+		seq_show_option(s, "locktable", args->ar_locktable);
 	if (args->ar_hostdata[0])
-		seq_printf(s, ",hostdata=%s", args->ar_hostdata);
+		seq_show_option(s, "hostdata", args->ar_hostdata);
 	if (args->ar_spectator)
 		seq_puts(s, ",spectator");
 	if (args->ar_localflocks)

fs/hfs/super.c +2 -2

@@ -136,9 +136,9 @@ static int hfs_show_options(struct seq_f
 	struct hfs_sb_info *sbi = HFS_SB(root->d_sb);
 
 	if (sbi->s_creator != cpu_to_be32(0x3f3f3f3f))
-		seq_printf(seq, ",creator=%.4s", (char *)&sbi->s_creator);
+		seq_show_option_n(seq, "creator", (char *)&sbi->s_creator, 4);
 	if (sbi->s_type != cpu_to_be32(0x3f3f3f3f))
-		seq_printf(seq, ",type=%.4s", (char *)&sbi->s_type);
+		seq_show_option_n(seq, "type", (char *)&sbi->s_type, 4);
 	seq_printf(seq, ",uid=%u,gid=%u",
 			from_kuid_munged(&init_user_ns, sbi->s_uid),
 			from_kgid_munged(&init_user_ns, sbi->s_gid));

fs/hfsplus/options.c +2 -2

@@ -218,9 +218,9 @@ int hfsplus_show_options(struct seq_file
 	struct hfsplus_sb_info *sbi = HFSPLUS_SB(root->d_sb);
 
 	if (sbi->creator != HFSPLUS_DEF_CR_TYPE)
-		seq_printf(seq, ",creator=%.4s", (char *)&sbi->creator);
+		seq_show_option_n(seq, "creator", (char *)&sbi->creator, 4);
 	if (sbi->type != HFSPLUS_DEF_CR_TYPE)
-		seq_printf(seq, ",type=%.4s", (char *)&sbi->type);
+		seq_show_option_n(seq, "type", (char *)&sbi->type, 4);
 	seq_printf(seq, ",umask=%o,uid=%u,gid=%u", sbi->umask,
 			from_kuid_munged(&init_user_ns, sbi->uid),
 			from_kgid_munged(&init_user_ns, sbi->gid));

fs/hostfs/hostfs_kern.c +1 -1

@@ -260,7 +260,7 @@ static int hostfs_show_options(struct se
 	size_t offset = strlen(root_ino) + 1;
 
 	if (strlen(root_path) > offset)
-		seq_printf(seq, ",%s", root_path + offset);
+		seq_show_option(seq, root_path + offset, NULL);
 
 	if (append)
 		seq_puts(seq, ",append");

fs/ocfs2/super.c +2 -2

@@ -1550,8 +1550,8 @@ static int ocfs2_show_options(struct seq
 		seq_printf(s, ",localflocks,");
 
 	if (osb->osb_cluster_stack[0])
-		seq_printf(s, ",cluster_stack=%.*s", OCFS2_STACK_LABEL_LEN,
-			   osb->osb_cluster_stack);
+		seq_show_option_n(s, "cluster_stack", osb->osb_cluster_stack,
+				  OCFS2_STACK_LABEL_LEN);
 	if (opts & OCFS2_MOUNT_USRQUOTA)
 		seq_printf(s, ",usrquota");
 	if (opts & OCFS2_MOUNT_GRPQUOTA)

fs/overlayfs/super.c +3 -3

@@ -588,10 +588,10 @@ static int ovl_show_options(struct seq_f
 	struct super_block *sb = dentry->d_sb;
 	struct ovl_fs *ufs = sb->s_fs_info;
 
-	seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
+	seq_show_option(m, "lowerdir", ufs->config.lowerdir);
 	if (ufs->config.upperdir) {
-		seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
-		seq_printf(m, ",workdir=%s", ufs->config.workdir);
+		seq_show_option(m, "upperdir", ufs->config.upperdir);
+		seq_show_option(m, "workdir", ufs->config.workdir);
 	}
 	return 0;
 }

fs/reiserfs/super.c +5 -3

@@ -714,18 +714,20 @@ static int reiserfs_show_options(struct
 		seq_puts(seq, ",acl");
 
 	if (REISERFS_SB(s)->s_jdev)
-		seq_printf(seq, ",jdev=%s", REISERFS_SB(s)->s_jdev);
+		seq_show_option(seq, "jdev", REISERFS_SB(s)->s_jdev);
 
 	if (journal->j_max_commit_age != journal->j_default_max_commit_age)
 		seq_printf(seq, ",commit=%d", journal->j_max_commit_age);
 
 #ifdef CONFIG_QUOTA
 	if (REISERFS_SB(s)->s_qf_names[USRQUOTA])
-		seq_printf(seq, ",usrjquota=%s", REISERFS_SB(s)->s_qf_names[USRQUOTA]);
+		seq_show_option(seq, "usrjquota",
+				REISERFS_SB(s)->s_qf_names[USRQUOTA]);
 	else if (opts & (1 << REISERFS_USRQUOTA))
 		seq_puts(seq, ",usrquota");
 	if (REISERFS_SB(s)->s_qf_names[GRPQUOTA])
-		seq_printf(seq, ",grpjquota=%s", REISERFS_SB(s)->s_qf_names[GRPQUOTA]);
+		seq_show_option(seq, "grpjquota",
+				REISERFS_SB(s)->s_qf_names[GRPQUOTA]);
 	else if (opts & (1 << REISERFS_GRPQUOTA))
 		seq_puts(seq, ",grpquota");
 	if (REISERFS_SB(s)->s_jquota_fmt) {

fs/xfs/xfs_super.c +2 -2

@@ -511,9 +511,9 @@ xfs_showargs(
 		seq_printf(m, "," MNTOPT_LOGBSIZE "=%dk", mp->m_logbsize >> 10);
 
 	if (mp->m_logname)
-		seq_printf(m, "," MNTOPT_LOGDEV "=%s", mp->m_logname);
+		seq_show_option(m, MNTOPT_LOGDEV, mp->m_logname);
 	if (mp->m_rtname)
-		seq_printf(m, "," MNTOPT_RTDEV "=%s", mp->m_rtname);
+		seq_show_option(m, MNTOPT_RTDEV, mp->m_rtname);
 
 	if (mp->m_dalign > 0)
 		seq_printf(m, "," MNTOPT_SUNIT "=%d",

include/linux/seq_file.h +35 -0

@@ -149,6 +149,41 @@ static inline struct user_namespace *seq
 #endif
 }
 
+/**
+ * seq_show_options - display mount options with appropriate escapes.
+ * @m: the seq_file handle
+ * @name: the mount option name
+ * @value: the mount option name's value, can be NULL
+ */
+static inline void seq_show_option(struct seq_file *m, const char *name,
+				   const char *value)
+{
+	seq_putc(m, ',');
+	seq_escape(m, name, ",= \t\n\\");
+	if (value) {
+		seq_putc(m, '=');
+		seq_escape(m, value, ", \t\n\\");
+	}
+}
+
+/**
+ * seq_show_option_n - display mount options with appropriate escapes
+ *		       where @value must be a specific length.
+ * @m: the seq_file handle
+ * @name: the mount option name
+ * @value: the mount option name's value, cannot be NULL
+ * @length: the length of @value to display
+ *
+ * This is a macro since this uses "length" to define the size of the
+ * stack buffer.
+ */
+#define seq_show_option_n(m, name, value, length) {	\
+	char val_buf[length + 1];			\
+	strncpy(val_buf, value, length);		\
+	val_buf[length] = '\0';				\
+	seq_show_option(m, name, val_buf);		\
+}
+
 #define SEQ_START_TOKEN ((void *)1)
 /*
  * Helpers for iteration over list_head-s in seq_files

kernel/cgroup.c +4 -3

@@ -1334,7 +1334,7 @@ static int cgroup_show_options(struct se
 
 	for_each_subsys(ss, ssid)
 		if (root->subsys_mask & (1 << ssid))
-			seq_printf(seq, ",%s", ss->name);
+			seq_show_option(seq, ss->name, NULL);
 	if (root->flags & CGRP_ROOT_NOPREFIX)
 		seq_puts(seq, ",noprefix");
 	if (root->flags & CGRP_ROOT_XATTR)

@@ -1342,13 +1342,14 @@ static int cgroup_show_options(struct se
 
 	spin_lock(&release_agent_path_lock);
 	if (strlen(root->release_agent_path))
-		seq_printf(seq, ",release_agent=%s", root->release_agent_path);
+		seq_show_option(seq, "release_agent",
+				root->release_agent_path);
 	spin_unlock(&release_agent_path_lock);
 
 	if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags))
 		seq_puts(seq, ",clone_children");
 	if (strlen(root->name))
-		seq_printf(seq, ",name=%s", root->name);
+		seq_show_option(seq, "name", root->name);
 	return 0;
 }

net/ceph/ceph_common.c +5 -2

@@ -517,8 +517,11 @@ int ceph_print_client_options(struct seq
 	struct ceph_options *opt = client->options;
 	size_t pos = m->count;
 
-	if (opt->name)
-		seq_printf(m, "name=%s,", opt->name);
+	if (opt->name) {
+		seq_puts(m, "name=");
+		seq_escape(m, opt->name, ", \t\n\\");
+		seq_putc(m, ',');
+	}
 	if (opt->key)
 		seq_puts(m, "secret=<hidden>,");

security/selinux/hooks.c +1 -1

@@ -1100,7 +1100,7 @@ static void selinux_write_opts(struct se
 		seq_puts(m, prefix);
 		if (has_comma)
 			seq_putc(m, '\"');
-		seq_puts(m, opts->mnt_opts[i]);
+		seq_escape(m, opts->mnt_opts[i], "\"\n\\");
 		if (has_comma)
 			seq_putc(m, '\"');
 	}

Patches currently in stable-queue which might be from [email protected] are

queue-4.2/fs-create-and-use-seq_show_option-for-escaping.patch