On Friday, August 07, 2015 04:41:50 PM Kees Cook wrote: > 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. > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > fs/ceph/super.c | 2 +- > fs/cifs/cifsfs.c | 6 +++--- > fs/ext3/super.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/overlayfs/super.c | 6 +++--- > fs/reiserfs/super.c | 8 +++++--- > fs/xfs/xfs_super.c | 4 ++-- > include/linux/seq_file.h | 34 ++++++++++++++++++++++++++++++++++ > kernel/cgroup.c | 7 ++++--- > net/ceph/ceph_common.c | 7 +++++-- > security/selinux/hooks.c | 2 +- > 16 files changed, 72 insertions(+), 32 deletions(-) The SELinux changes look fine to me. Acked-by: Paul Moore <paul@xxxxxxxxxxxxxx> -- paul moore www.paul-moore.com -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
