[PATCH 3.19.y-ckt 098/156] fs: create and use seq_show_option for escaping

From: Kamal Mostafa
Date: Tue Oct 20 2015 - 17:39:55 EST

3.19.8-ckt8 -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>
[ kamal: backport to 3.19-stable: dropped net/ceph/ceph_common.c changes;
context ]
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/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 ++++---
security/selinux/hooks.c | 2 +-
14 files changed, 67 insertions(+), 28 deletions(-)

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index 50f06cd..c132ce8 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 d72fe37..e5a25d1 100644
--- a/fs/cifs/cifsfs.c
+++ b/fs/cifs/cifsfs.c
@@ -394,17 +394,17 @@ 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 47f678c..f46b29e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1736,10 +1736,10 @@ 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 5b327f8..0043f62 100644
--- a/fs/gfs2/super.c
+++ b/fs/gfs2/super.c
@@ -1334,11 +1334,11 @@ static int gfs2_show_options(struct seq_file *s, struct dentry *root)
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)
diff --git a/fs/hfs/super.c b/fs/hfs/super.c
index eee7206..410b65e 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 c90b72e..bb806e5 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 fd62cae..2e887ee 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 8372317..a489416 100644
--- a/fs/ocfs2/super.c
+++ b/fs/ocfs2/super.c
@@ -1575,8 +1575,8 @@ 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/overlayfs/super.c b/fs/overlayfs/super.c
index f16d318..ab3efa1 100644
--- a/fs/overlayfs/super.c
+++ b/fs/overlayfs/super.c
@@ -431,9 +431,9 @@ static int ovl_show_options(struct seq_file *m, struct dentry *dentry)
struct super_block *sb = dentry->d_sb;
struct ovl_fs *ufs = sb->s_fs_info;

- seq_printf(m, ",lowerdir=%s", ufs->config.lowerdir);
- seq_printf(m, ",upperdir=%s", ufs->config.upperdir);
- seq_printf(m, ",workdir=%s", ufs->config.workdir);
+ seq_show_option(m, "lowerdir", ufs->config.lowerdir);
+ seq_show_option(m, "upperdir", ufs->config.upperdir);
+ seq_show_option(m, "workdir", ufs->config.workdir);
return 0;
}

diff --git a/fs/reiserfs/super.c b/fs/reiserfs/super.c
index 71fbbe3..2067cba 100644
--- a/fs/reiserfs/super.c
+++ b/fs/reiserfs/super.c
@@ -714,18 +714,20 @@ 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 19cbda1..8e8ff32 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -524,9 +524,9 @@ 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 cf6a9da..75aad5b 100644
--- a/include/linux/seq_file.h
+++ b/include/linux/seq_file.h
@@ -173,6 +173,41 @@ 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 00e19f7..87deef1 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1319,7 +1319,7 @@ static int cgroup_show_options(struct seq_file *seq,

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)
@@ -1327,13 +1327,14 @@ 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 7634300..903b039 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1109,7 +1109,7 @@ 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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