[PATCH 3.16.y-ckt 073/133] fs: create and use seq_show_option for escaping

From: Luis Henriques
Date: Wed Sep 30 2015 - 06:18:23 EST

3.16.7-ckt18 -stable review patch. If anyone has any objections, please let me know.

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

From: Kees Cook <keescook@xxxxxxxxxxxx>

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@xxxxxxxxxxxxxxxxxxxx: add lost chunk, per Kees]
[keescook@xxxxxxxxxxxx: seq_show_option should be using const parameters]
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
Acked-by: Jan Kara <jack@xxxxxxxx>
Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx>
Cc: J. R. Okajima <hooanon05g@xxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
[ luis: backported to 3.16:
- dropped changes to fs/overlayfs/super.c, net/ceph/ceph_common.c and to
cgroup_show_options() in kernel/cgroup.c
- adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@xxxxxxxxxxxxx>
---
fs/ceph/super.c | 3 ++-
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/reiserfs/super.c | 8 +++++---
fs/xfs/xfs_super.c | 4 ++--
include/linux/seq_file.h | 35 +++++++++++++++++++++++++++++++++++
kernel/cgroup.c | 5 +++--
security/selinux/hooks.c | 2 +-
13 files changed, 63 insertions(+), 24 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 8503ec130c15..526db4502aa6 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -483,7 +483,8 @@ 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 888398067420..d678cda1cd81 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -382,17 +382,17 @@ cifs_show_options(struct seq_file *s, struct dentry *root)
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;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index cf977e2f8a6f..a8f6f6a358ce 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1750,10 +1750,10 @@ 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]);
#endif
}

diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
index 1319b5c4ec68..b844cf82e0f9 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1302,11 +1302,11 @@ 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 eee7206c38d1..410b65eea683 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -135,9 +135,9 @@ 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",
from_kuid_munged(&init_user_ns, sbi->s_uid),
from_kgid_munged(&init_user_ns, sbi->s_gid));
diff --git a/fs/hfsplus/options.c b/fs/hfsplus/options.c
index c90b72ee676d..bb806e58c977 100644
--- a/fs/hfsplus/options.c
+++ b/fs/hfsplus/options.c
@@ -218,9 +218,9 @@ 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,
from_kuid_munged(&init_user_ns, sbi->uid),
from_kgid_munged(&init_user_ns, sbi->gid));
diff --git a/fs/hostfs/hostfs_kern.c b/fs/hostfs/hostfs_kern.c
index bb529f3b7f2b..456f60e2552e 100644
--- a/fs/hostfs/hostfs_kern.c
+++ b/fs/hostfs/hostfs_kern.c
@@ -255,7 +255,7 @@ 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 ddb662b32447..34690360ff33 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -1564,8 +1564,8 @@ 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 27575041bea3..48c6924eba05 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -710,18 +710,20 @@ 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 8f0333b3f7a0..2637010a6224 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -529,9 +529,9 @@ 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 52e0097f61f0..6288341db62d 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -158,6 +158,41 @@ static inline struct user_namespace *seq_user_ns(struct seq_file *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
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 44fadfb287bf..58fd665d1217 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1248,13 +1248,14 @@ static int cgroup_show_options(struct seq_file *seq,

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;
}

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 9a23a7cccdc4..af2d5124f99c 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1100,7 +1100,7 @@ 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, '\"');
}
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