Subject: Re: [PATCH ghak90 V6 03/10] audit: read container ID of a process

From: [email-masked] (Eric W. Biederman)
Date: Fri, 19 Jul 2019 11:03:35 -0500

Richard Guy Briggs <[email-masked]> writes:

> Add support for reading the audit container identifier from the proc
> filesystem.
>
> This is a read from the proc entry of the form
> /proc/PID/audit_containerid where PID is the process ID of the task
> whose audit container identifier is sought.
>
> The read expects up to a u64 value (unset: 18446744073709551615).
>
> This read requires CAP_AUDIT_CONTROL.

This scares me.    As this seems to make it easy to reuse an audit
containerid for non-audit purporses.

I would think it would be safer and easier to poke audit and ask it to
log a message with your audit container id.

Eric

> Signed-off-by: Richard Guy Briggs <[email-masked]>
> Acked-by: Serge Hallyn <[email-masked]>
> Acked-by: Neil Horman <[email-masked]>
> Reviewed-by: Ondrej Mosnacek <[email-masked]>
> ---
>  fs/proc/base.c | 25 ++++++++++++++++++++++---
>  1 file changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 43fd0c4b87de..acc70239d0cb 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1211,7 +1211,7 @@ static ssize_t oom_score_adj_write(struct file *file, const char __user *buf,
>  };
>  
>  #ifdef CONFIG_AUDIT
> -#define TMPBUFLEN 11
> +#define TMPBUFLEN 21
>  static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
>  				  size_t count, loff_t *ppos)
>  {
> @@ -1295,6 +1295,24 @@ static ssize_t proc_sessionid_read(struct file * file, char __user * buf,
>  	.llseek		= generic_file_llseek,
>  };
>  
> +static ssize_t proc_contid_read(struct file *file, char __user *buf,
> +				  size_t count, loff_t *ppos)
> +{
> +	struct inode *inode = file_inode(file);
> +	struct task_struct *task = get_proc_task(inode);
> +	ssize_t length;
> +	char tmpbuf[TMPBUFLEN];
> +
> +	if (!task)
> +		return -ESRCH;
> +	/* if we don't have caps, reject */
> +	if (!capable(CAP_AUDIT_CONTROL))
> +		return -EPERM;
> +	length = scnprintf(tmpbuf, TMPBUFLEN, "%llu", audit_get_contid(task));
> +	put_task_struct(task);
> +	return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
> +}
> +
>  static ssize_t proc_contid_write(struct file *file, const char __user *buf,
>  				   size_t count, loff_t *ppos)
>  {
> @@ -1325,6 +1343,7 @@ static ssize_t proc_contid_write(struct file *file, const char __user *buf,
>  }
>  
>  static const struct file_operations proc_contid_operations = {
> +	.read		= proc_contid_read,
>  	.write		= proc_contid_write,
>  	.llseek		= generic_file_llseek,
>  };
> @@ -3067,7 +3086,7 @@ static int proc_stack_depth(struct seq_file *m, struct pid_namespace *ns,
>  #ifdef CONFIG_AUDIT
>  	REG("loginuid",   S_IWUSR|S_IRUGO, proc_loginuid_operations),
>  	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
> -	REG("audit_containerid", S_IWUSR, proc_contid_operations),
> +	REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
>  #endif
>  #ifdef CONFIG_FAULT_INJECTION
>  	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),
> @@ -3466,7 +3485,7 @@ static int proc_tid_comm_permission(struct inode *inode, int mask)
>  #ifdef CONFIG_AUDIT
>  	REG("loginuid",  S_IWUSR|S_IRUGO, proc_loginuid_operations),
>  	REG("sessionid",  S_IRUGO, proc_sessionid_operations),
> -	REG("audit_containerid", S_IWUSR, proc_contid_operations),
> +	REG("audit_containerid", S_IWUSR|S_IRUSR, proc_contid_operations),
>  #endif
>  #ifdef CONFIG_FAULT_INJECTION
>  	REG("make-it-fail", S_IRUGO|S_IWUSR, proc_fault_inject_operations),