[PATCH 3.4 26/92] fs: create and use seq_show_option for escaping

[lizf@kernel.org]

From: Kees Cook <keescook@chromium.org>

3.4.112-rc1 review patch.  If anyone has any objections, please let me know.

------------------


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.

[akpm@linux-foundation.org: add lost chunk, per Kees]
[keescook@chromium.org: seq_show_option should be using const parameters]
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Acked-by: Jan Kara <jack@suse.com>
Acked-by: Paul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[lizf: Backported to 3.4:
 - adjust context
 - one more place in ceph needs to be changed
 - drop changes to overlayfs
 - drop showing vers in cifs]
Signed-off-by: Zefan Li <lizefan@huawei.com>
---
 fs/ceph/super.c          |  8 +++++---
 fs/cifs/cifsfs.c         |  4 ++--
 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/reiserfs/super.c      |  8 +++++---
 fs/xfs/xfs_super.c       |  4 ++--
 include/linux/seq_file.h | 35 +++++++++++++++++++++++++++++++++++
 kernel/cgroup.c          |  7 ++++---
 security/selinux/hooks.c |  2 +-
 13 files changed, 66 insertions(+), 26 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index f4fa5cf..e5eacd9 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -383,8 +383,10 @@ static int ceph_show_options(struct seq_file *m, struct dentry *root)
 	if (opt->flags & CEPH_OPT_NOCRC)
 		seq_puts(m, ",nocrc");
 
-	if (opt->name)
-		seq_printf(m, ",name=%s", opt->name);
+	if (opt->name) {
+		seq_puts(m, ",name=");
+		seq_escape(m, opt->name, ", \t\n\\");
+	}
 	if (opt->key)
 		seq_puts(m, ",secret=<hidden>");
 
@@ -429,7 +431,7 @@ static int ceph_show_options(struct seq_file *m, struct dentry *root)
 	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;
 }
 
diff --git a/fs/cifs/cifsfs.c b/fs/cifs/cifsfs.c
index c0f65e8..5b730ba 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -373,10 +373,10 @@ cifs_show_options(struct seq_file *s, struct dentry *root)
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MULTIUSER)
 		seq_printf(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;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2e26a54..3de888c3 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1682,10 +1682,10 @@ static inline void ext4_show_quota_options(struct seq_file *seq,
 	}
 
 	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]);
 
 	if (test_opt(sb, USRQUOTA))
 		seq_puts(seq, ",usrquota");
diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 6172fa7..4db9a9a 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1298,11 +1298,11 @@ static int gfs2_show_options(struct seq_file *s, struct dentry *root)
 	if (is_ancestor(root, sdp->sd_master_dir))
 		seq_printf(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_printf(s, ",spectator");
 	if (args->ar_localflocks)
diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index 7b4c537..be0e218 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -138,9 +138,9 @@ static int hfs_show_options(struct seq_file *seq, struct dentry *root)
 	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", sbi->s_uid, sbi->s_gid);
 	if (sbi->s_file_umask != 0133)
 		seq_printf(seq, ",file_umask=%o", sbi->s_file_umask);
diff --git a/fs/hfsplus/options.c b/fs/hfsplus/options.c
index 06fa561..38e41d0 100644
--- a/fs/hfsplus/options.c
+++ b/fs/hfsplus/options.c
@@ -211,9 +211,9 @@ int hfsplus_show_options(struct seq_file *seq, struct dentry *root)
 	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,
 		sbi->uid, sbi->gid);
 	if (sbi->part >= 0)
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index 07c516b..fe63b15 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -264,7 +264,7 @@ static int hostfs_show_options(struct seq_file *seq, struct dentry *root)
 	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);
 
 	return 0;
 }
diff --git a/fs/ocfs2/super.c b/fs/ocfs2/super.c
index 68f4541..91a0020 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -1578,8 +1578,8 @@ static int ocfs2_show_options(struct seq_file *s, struct dentry *root)
 		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)
diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index 8169be9..e12357b 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -645,18 +645,20 @@ static int reiserfs_show_options(struct seq_file *seq, struct dentry *root)
 		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) {
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index dab9a5f..d6c787d 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -523,9 +523,9 @@ 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",
diff --git a/include/linux/seq_file.h b/include/linux/seq_file.h
index fc61854..149b92f 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -127,6 +127,41 @@ int seq_put_decimal_ull(struct seq_file *m, char delimiter,
 int seq_put_decimal_ll(struct seq_file *m, char delimiter,
 			long long num);
 
+/**
+ * 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
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 34eda95..7ff5702 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1071,15 +1071,16 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
 
 	mutex_lock(&cgroup_root_mutex);
 	for_each_subsys(root, ss)
-		seq_printf(seq, ",%s", ss->name);
+		seq_show_option(seq, ss->name, NULL);
 	if (test_bit(ROOT_NOPREFIX, &root->flags))
 		seq_puts(seq, ",noprefix");
 	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);
 	if (clone_children(&root->top_cgroup))
 		seq_puts(seq, ",clone_children");
 	if (strlen(root->name))
-		seq_printf(seq, ",name=%s", root->name);
+		seq_show_option(seq, "name", root->name);
 	mutex_unlock(&cgroup_root_mutex);
 	return 0;
 }
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index cbae6d3..312d2fb 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1012,7 +1012,7 @@ static void selinux_write_opts(struct seq_file *m,
 		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, '\"');
 	}
-- 
1.9.1