On Thu, 20 Jun 2019 18:19:40 -0700
Matthew Garrett <matthewgarr...@google.com> wrote:
> Tracefs may release more information about the kernel than desirable, so
> restrict it when the kernel is locked down in confidentiality mode by
> preventing open().
>
> Signed-off-by: Matthew Garrett <mj...@google.com>
> Cc: Steven Rostedt <rost...@goodmis.org>
> ---
> fs/tracefs/inode.c | 41 +++++++++++++++++++++++++++++++++++-
> include/linux/security.h | 1 +
> security/lockdown/lockdown.c | 1 +
> 3 files changed, 42 insertions(+), 1 deletion(-)
>
> diff --git a/fs/tracefs/inode.c b/fs/tracefs/inode.c
> index 7098c49f3693..f6c04fa8e415 100644
> --- a/fs/tracefs/inode.c
> +++ b/fs/tracefs/inode.c
> @@ -24,6 +24,7 @@
> #include <linux/parser.h>
> #include <linux/magic.h>
> #include <linux/slab.h>
> +#include <linux/security.h>
>
> #define TRACEFS_DEFAULT_MODE 0700
>
> @@ -31,6 +32,21 @@ static struct vfsmount *tracefs_mount;
> static int tracefs_mount_count;
> static bool tracefs_registered;
>
> +static int default_open_file(struct inode *inode, struct file *filp)
> +{
> + struct dentry *dentry = filp->f_path.dentry;
> + struct file_operations *real_fops;
> +
> + if (!dentry)
> + return -EINVAL;
> +
> + if (security_is_locked_down(LOCKDOWN_TRACEFS))
> + return -EPERM;
> +
> + real_fops = dentry->d_fsdata;
> + return real_fops->open(inode, filp);
> +}
> +
> static ssize_t default_read_file(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> {
> @@ -50,6 +66,13 @@ static const struct file_operations
> tracefs_file_operations = {
> .llseek = noop_llseek,
> };
>
> +static const struct file_operations tracefs_proxy_file_operations = {
> + .read = default_read_file,
> + .write = default_write_file,
> + .open = default_open_file,
> + .llseek = noop_llseek,
> +};
This appears to be unused.
> +
> static struct tracefs_dir_ops {
> int (*mkdir)(const char *name);
> int (*rmdir)(const char *name);
> @@ -225,6 +248,12 @@ static int tracefs_apply_options(struct super_block *sb)
> return 0;
> }
>
> +static void tracefs_destroy_inode(struct inode *inode)
> +{
> + if (S_ISREG(inode->i_mode))
> + kfree(inode->i_fop);
> +}
> +
> static int tracefs_remount(struct super_block *sb, int *flags, char *data)
> {
> int err;
> @@ -260,6 +289,7 @@ static int tracefs_show_options(struct seq_file *m,
> struct dentry *root)
>
> static const struct super_operations tracefs_super_operations = {
> .statfs = simple_statfs,
> + .destroy_inode = tracefs_destroy_inode,
> .remount_fs = tracefs_remount,
> .show_options = tracefs_show_options,
> };
> @@ -393,6 +423,7 @@ struct dentry *tracefs_create_file(const char *name,
> umode_t mode,
> {
> struct dentry *dentry;
> struct inode *inode;
> + struct file_operations *proxy_fops;
>
> if (!(mode & S_IFMT))
> mode |= S_IFREG;
> @@ -406,8 +437,16 @@ struct dentry *tracefs_create_file(const char *name,
> umode_t mode,
> if (unlikely(!inode))
> return failed_creating(dentry);
>
> + proxy_fops = kzalloc(sizeof(struct file_operations), GFP_KERNEL);
> + if (!proxy_fops)
> + return failed_creating(dentry);
> +
> + dentry->d_fsdata = fops ? (void *)fops :
> + (void *)&tracefs_file_operations;
> + memcpy(proxy_fops, dentry->d_fsdata, sizeof(struct file_operations));
> + proxy_fops->open = default_open_file;
> inode->i_mode = mode;
> - inode->i_fop = fops ? fops : &tracefs_file_operations;
> + inode->i_fop = proxy_fops;
I think the above would look cleaner as:
if (!fops)
fops = &tracefs_file_operations;
dentry->d_fsdata = (void *)fops;
memcpy(proxy_fops, fops, sizeof(*proxy_fops);
proxy_fops->open = default_open_file;
-- Steve
> inode->i_private = data;
> d_instantiate(dentry, inode);
> fsnotify_create(dentry->d_parent->d_inode, dentry);
> diff --git a/include/linux/security.h b/include/linux/security.h
> index 2563a9e3b415..040e7fc33397 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -100,6 +100,7 @@ enum lockdown_reason {
> LOCKDOWN_KPROBES,
> LOCKDOWN_BPF,
> LOCKDOWN_PERF,
> + LOCKDOWN_TRACEFS,
> LOCKDOWN_CONFIDENTIALITY_MAX,
> };
>
> diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
> index a6f7b0770e78..7dc601f06cd3 100644
> --- a/security/lockdown/lockdown.c
> +++ b/security/lockdown/lockdown.c
> @@ -36,6 +36,7 @@ static char
> *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
> [LOCKDOWN_KPROBES] = "use of kprobes",
> [LOCKDOWN_BPF] = "use of bpf",
> [LOCKDOWN_PERF] = "unsafe use of perf",
> + [LOCKDOWN_TRACEFS] = "use of tracefs",
> [LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
> };
>
