Re: [RFC PATCH ghak9 2/3] audit: Add a function to log the path of an fd

Ondrej Mosnacek
2018-07-16T08:28:59Z

On Fri, Jul 13, 2018 at 5:17 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> On 2018-07-12 13:36, Ondrej Mosnacek wrote:
> > The function logs an FD_PATH record that is associated with the current
> > syscall. The record associates the given file descriptor with the
> > current path of the file under it (if it is possible to retrieve such
> > path). The reader of the log can then logically connect this information
> > to the syscall arguments from the SYSCALL record (based on the syscall
> > type).
> >
> > Record format:
> > type=FD_PATH msg=audit(...): fd=<file descriptor> path=<file path>
> >
> > Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
> > ---
> > include/linux/audit.h | 10 ++++++++++
> > kernel/auditsc.c | 36 ++++++++++++++++++++++++++++++++++++
> > 2 files changed, 46 insertions(+)
> >
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index 9334fbef7bae..95d338bb603a 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -356,6 +356,7 @@ extern void __audit_log_capset(const struct cred *new, const struct cred *old);
> > extern void __audit_mmap_fd(int fd, int flags);
> > extern void __audit_log_kern_module(char *name);
> > extern void __audit_fanotify(unsigned int response);
> > +extern void __audit_fd_path(int fd);
> >
> > static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp)
> > {
> > @@ -458,6 +459,12 @@ static inline void audit_fanotify(unsigned int response)
> > __audit_fanotify(response);
> > }
> >
> > +static inline void audit_fd_path(int fd)
> > +{
> > + if (fd >= 0 && !audit_dummy_context())
>
> Isn't an fd of 0 valid?

It is treated as valid by the above condition (it only rejects
negative values), so I'm not sure if you mean "valid" or "invalid"...
I suppose an fd of 0 is unlikely to be used as dirfd in openat(2) et
al., but in general it is a valid fd and I don't think we should
explicitly exclude it here. The corresponding syscalls' input checks
will already filter out values that are invalid for them.

>
> > + __audit_fd_path(fd);
> > +}
> > +
> > extern int audit_n_rules;
> > extern int audit_signals;
> > #else /* CONFIG_AUDITSYSCALL */
> > @@ -584,6 +591,9 @@ static inline void audit_log_kern_module(char *name)
> > static inline void audit_fanotify(unsigned int response)
> > { }
> >
> > +static inline void audit_fd_path(int fd)
> > +{ }
> > +
> > static inline void audit_ptrace(struct task_struct *t)
> > { }
> > #define audit_n_rules 0
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index d762e0b8160e..82dad69213a2 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -74,6 +74,8 @@
> > #include <linux/string.h>
> > #include <linux/uaccess.h>
> > #include <linux/fsnotify_backend.h>
> > +#include <linux/file.h>
> > +#include <linux/dcache.h>
> > #include <uapi/linux/limits.h>
> >
> > #include "audit.h"
> > @@ -2422,6 +2424,40 @@ void __audit_fanotify(unsigned int response)
> > AUDIT_FANOTIFY, "resp=%u", response);
> > }
> >
> > +void __audit_fd_path(int fd)
> > +{
> > + struct audit_buffer *ab;
> > + struct file *file;
> > + char *buf, *path;
> > +
> > + if (!audit_enabled)
> > + return;
> > +
> > + file = fget_raw(fd);
> > + if (!file)
> > + return;
> > +
> > + buf = kmalloc(PATH_MAX, GFP_KERNEL);
> > + if (!buf)
>
> I think we need an fput(file) here.

Indeed we do, will fix in next revision.

>
> > + return;
> > +
> > + path_get(&file->f_path);
> > + path = d_absolute_path(&file->f_path, buf, PATH_MAX);
> > + path_put(&file->f_path);
> > + fput(file);
> > + if (!path || IS_ERR(path))
> > + goto free_buf;
> > +
> > + ab = audit_log_start(audit_context(), GFP_KERNEL, AUDIT_FD_PATH);
> > + if (unlikely(!ab))
> > + goto free_buf;
> > + audit_log_format(ab, "fd=%i path=", fd);
> > + audit_log_untrustedstring(ab, path);
> > + audit_log_end(ab);
> > +free_buf:
> > + kfree(buf);
> > +}
> > +
> > static void audit_log_task(struct audit_buffer *ab)
> > {
> > kuid_t auid, uid;
>
> - 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

--
Ondrej Mosnacek <omosnace at redhat dot com>
Associate Software Engineer, Security Technologies
Red Hat, Inc.