[PATCH 3.13.y-ckt 57/85] fs: create and use seq_show_option for escaping

From: Kamal Mostafa
Date: Tue Oct 20 2015 - 18:35:48 EST

3.13.11-ckt28 -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>
Signed-off-by: Kamal Mostafa <kamal@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 6a0951e..c495508 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -460,7 +460,8 @@ 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 7c6b73c..c90d4bd 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -390,17 +390,17 @@ 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_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 a07af5b..c261beb 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1744,10 +1744,10 @@ 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 35da5b1..b05f395 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1258,11 +1258,11 @@ 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 2d2039e..52cd187 100644
--- a/fs/hfs/super.c
+++ b/fs/hfs/super.c
@@ -134,9 +134,9 @@ 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 968eab5..beaae4e 100644
--- a/fs/hfsplus/options.c
+++ b/fs/hfsplus/options.c
@@ -219,9 +219,9 @@ 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 db23ce1..5d2585a 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 c414929..3e12b38 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 3ead145..b2506ca 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -690,18 +690,20 @@ 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 d971f49..26d7693 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 52e0097..6288341 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 6f2aae9..c02e4d7 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1107,11 +1107,12 @@ static int cgroup_show_options(struct seq_file *seq, struct dentry *dentry)
if (root->flags & CGRP_ROOT_XATTR)
seq_puts(seq, ",xattr");
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 (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->top_cgroup.flags))
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 3138402..3b38a36 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1101,7 +1101,7 @@ 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

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