Re: [PATCH v2] ima: fix showing large 'violations' or 'runtime_measurements_count'

[Mimi Zohar <zohar@linux.ibm.com>]

On Thu, 2018-10-04 at 15:28 -0700, Eric Biggers wrote:
> On Thu, Oct 04, 2018 at 06:21:35PM -0400, Mimi Zohar wrote:
> > On Wed, 2018-10-03 at 17:01 -0700, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@google.com>
> > > 
> > > The 12 character temporary buffer is not necessarily long enough to hold
> > > a 'long' value.  Increase it.
> > > 
> > > Signed-off-by: Eric Biggers <ebiggers@google.com>
> > > ---
> > >  security/integrity/ima/ima_fs.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/security/integrity/ima/ima_fs.c b/security/integrity/ima/ima_fs.c
> > > index ae9d5c766a3ce..4b50fe9c18edd 100644
> > > --- a/security/integrity/ima/ima_fs.c
> > > +++ b/security/integrity/ima/ima_fs.c
> > > @@ -42,14 +42,15 @@ static int __init default_canonical_fmt_setup(char *str)
> > >  __setup("ima_canonical_fmt", default_canonical_fmt_setup);
> > > 
> > >  static int valid_policy = 1;
> > > -#define TMPBUFLEN 12
> > > +
> > >  static ssize_t ima_show_htable_value(char __user *buf, size_t count,
> > >  				     loff_t *ppos, atomic_long_t *val)
> > >  {
> > > -	char tmpbuf[TMPBUFLEN];
> > > +	/* temporary buffer that is plenty long enough */

This comment is useless.

> > > +	char tmpbuf[32];

char tmpbuf[32];	/* string size needed for largest long value */

> > 
> > If the maximum value of long is 9,223,372,036,854,775,807, the largest
> > string needed to represent this value is 20 characters.  Should 32 be
> > hardcoded like this?
> 
> There's no real cost to overestimating slightly here, and it's better than
> trying to count exactly and getting it wrong (hint: it's actually more than 20
> characters).

Please explain how it is more than 20 characters.

Mimi