Commit a068acf2 authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

fs: create and use seq_show_option for escaping 



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: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarSerge Hallyn <serge.hallyn@canonical.com>
Acked-by: default avatarJan Kara <jack@suse.com>
Acked-by: default avatarPaul Moore <paul@paul-moore.com>
Cc: J. R. Okajima <hooanon05g@gmail.com>
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 46359295

fs/ceph/super.c

+1 −1
Original line number Diff line number Diff line
@@ -479,7 +479,7 @@ 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;

}

fs/cifs/cifsfs.c

+3 −3
Original line number Diff line number Diff line
@@ -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;

fs/ext4/super.c

+2 −2
Original line number Diff line number Diff line
@@ -1776,10 +1776,10 @@ 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

}

fs/gfs2/super.c

+3 −3
Original line number Diff line number Diff line
@@ -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)

fs/hfs/super.c

+2 −2
Original line number Diff line number Diff line
@@ -136,9 +136,9 @@ 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));

CRA Git | Maintained and supported by SUSTech CRA and CCSE