Re: [PATCH ghak90 V5 03/10] audit: read container ID of a process

[Neil Horman <nhorman@tuxdriver.com>]

On Mon, Mar 18, 2019 at 02:17:21PM -0400, Richard Guy Briggs wrote:
> On 2019-03-18 07:10, Neil Horman wrote:
> > On Fri, Mar 15, 2019 at 02:29:51PM -0400, Richard Guy Briggs wrote:
> > > 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.
> > > 
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > Acked-by: Serge Hallyn <serge@hallyn.com>
> > > ---
> > >  fs/proc/base.c | 23 +++++++++++++++++++++--
> > >  1 file changed, 21 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > > index 2505c46c8701..0b833cbdf5b6 100644
> > > --- a/fs/proc/base.c
> > > +++ b/fs/proc/base.c
> > > @@ -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*2];
> > > +
> > Sorry, didn't notice this previously, but..
> > Why *2 here?  Its not wrong per-se, but would it be better to just change
> > TMPBUFLEN to be 22 bytes unilaterally?  Its only ever used on stack calls that
> > arent that deep, and then you won't have to think about adjusting this call site
> > if you ever change the value of TMPBUFLEN in the future.
> 
> TMPBUFLEN is 11 to accomodate a decimal representation of a u32 with
> terminating NULL.  Since the contid is a u64, it was least disruptive
> and made sense to me to just double it.  I could define a TMPBUFLEN2 to
> be 21 if you prefer?
> 
I'm not adamant on any particular change, just noticing the inconsistency.  I
usually write macro buffer sizes to accomodate the largest string I plan to
hold, so it can be used ubiquitously when the overage is small and transiently
allocated, but if you feel like the space would be better conserved a TMPBUFLEN/
TMPBUFLEN2 approach would be fine (or a TMPBUFLENU32 / TMPBUFLENU64 macro set).

Its not anything that needs fixing now, just an observation for clean up at some
future point.
Neil

> > I'm fine with doing this in another patch later, but it seems like a worthwhile
> > cleanup
> > 
> > functionality looks good beyond that nit.
> > 
> > > +	if (!task)
> > > +		return -ESRCH;
> > > +	/* if we don't have caps, reject */
> > > +	if (!capable(CAP_AUDIT_CONTROL))
> > > +		return -EPERM;
> > > +	length = scnprintf(tmpbuf, TMPBUFLEN*2, "%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,
> > >  };
> > > @@ -3039,7 +3058,7 @@ 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),
> > > @@ -3428,7 +3447,7 @@ 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),
> > > -- 
> > > 1.8.3.1
> > > 
> > > 
> > Acked-by: Neil Horman <nhorman@tuxdriver.com>
> > 
> 
> - RGB
> 
> --
> Richard Guy Briggs <rgb@redhat.com>
> Sr. S/W Engineer, Kernel Security, Base Operating Systems
> Remote, Ottawa, Red Hat Canada
> IRC: rgb, SunRaycer
> Voice: +1.647.777.2635, Internal: (81) 32635
>