Re: [PATCH ghak109 V1] audit: link integrity evm_write_xattrs record to syscall event

Mimi Zohar
2019-03-26T15:12:35Z

On Wed, 2019-03-20 at 20:50 -0400, Richard Guy Briggs wrote:
> On 2019-03-20 19:48, Paul Moore wrote:
> > On Sat, Mar 16, 2019 at 8:10 AM Richard Guy Briggs <rgb@redhat.com> wrote:
> > > In commit fa516b66a1bf ("EVM: Allow runtime modification of the set of
> > > verified xattrs"), the call to audit_log_start() is missing a context to
> > > link it to an audit event. Since this event is in user context, add
> > > the process' syscall context to the record.
> > >
> > > In addition, the orphaned keyword "locked" appears in the record.
> > > Normalize this by changing it to "xattr=(locked)".
> > >
> > > Please see the github issue
> > > https://github.com/linux-audit/audit-kernel/issues/109
> > >
> > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > > ---
> > > security/integrity/evm/evm_secfs.c | 5 +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/security/integrity/evm/evm_secfs.c b/security/integrity/evm/evm_secfs.c
> > > index 015aea8fdf1e..4171d174e9da 100644
> > > --- a/security/integrity/evm/evm_secfs.c
> > > +++ b/security/integrity/evm/evm_secfs.c
> > > @@ -192,7 +192,8 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
> > > if (count > XATTR_NAME_MAX)
> > > return -E2BIG;
> > >
> > > - ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_INTEGRITY_EVM_XATTR);
> > > + ab = audit_log_start(audit_context(), GFP_KERNEL,
> > > + AUDIT_INTEGRITY_EVM_XATTR);
> >
> > This part is fine.
> >
> > > if (!ab)
> > > return -ENOMEM;
> > >
> > > @@ -222,7 +223,7 @@ static ssize_t evm_write_xattrs(struct file *file, const char __user *buf,
> > > inode_lock(inode);
> > > err = simple_setattr(evm_xattrs, &newattrs);
> > > inode_unlock(inode);
> > > - audit_log_format(ab, "locked");
> > > + audit_log_format(ab, "xattr=(locked)");
> >
> > Two things come to mind:
> >
> > * While we can clearly trust the string above, should we be logging
> > the xattr field value as an untrusted string so it is consistent with
> > how we record other xattr names?
>
> That would be a question for Steve.
>
> > * I'm not sure you can ever have parens in a xattr (I would hope not),
> > but if we are going to use the xattr field, perhaps we should simply
> > stick with the name as provided (".") so we don't ever run afoul of
> > xattr names? I'm curious to hear what the IMA/EVM folks think of
> > this.
>
> The legal xaddr names start with XATTR_SECURITY_PREFIX which is
> "security." so there is no danger of collision with legal names, but I
> suppose someone could try to use "(locked)" as a name which would look
> identical but fail with a different res= number. I think I prefer your
> idea of printing the given value verbatim.

I really don't have a preference - "locked", "(locked)", "." or "(.)".
Any of them is fine.

Thanks!

Mimi