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Re: [PATCH v2 2/5] Don't return stale data from fbsd_pid_to_exec_file for kernel processes.
On Thursday, January 04, 2018 09:57:00 PM Simon Marchi wrote:
> On 2018-01-03 08:49 PM, John Baldwin wrote:
> > For processes without an associated executable (such as kernel processes),
> > the kern.proc.pathname.<pid> system control node returns a length of zero
> > without modifying the user's buffer. Detect this case and return NULL
> > rather than the previous contents of the static buffer 'buf'.
> >
> > gdb/ChangeLog:
> >
> > * fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
> > NULL for an empty pathname.
> > ---
> > gdb/ChangeLog | 5 +++++
> > gdb/fbsd-nat.c | 2 +-
> > 2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/gdb/ChangeLog b/gdb/ChangeLog
> > index 29cfbb287b..804dd4f402 100644
> > --- a/gdb/ChangeLog
> > +++ b/gdb/ChangeLog
> > @@ -1,3 +1,8 @@
> > +2018-01-03 John Baldwin <jhb@FreeBSD.org>
> > +
> > + * fbsd-nat.c (fbsd_pid_to_exec_file) [KERN_PROC_PATHNAME]: Return
> > + NULL for an empty pathname.
> > +
> > 2018-01-03 John Baldwin <jhb@FreeBSD.org>
> >
> > * fbsd-tdep.c (KVE_STRUCTSIZE, KVE_START, KVE_END, KVE_OFFSET)
> > diff --git a/gdb/fbsd-nat.c b/gdb/fbsd-nat.c
> > index ec4eed9abe..7b1d1bf148 100644
> > --- a/gdb/fbsd-nat.c
> > +++ b/gdb/fbsd-nat.c
> > @@ -63,7 +63,7 @@ fbsd_pid_to_exec_file (struct target_ops *self, int pid)
> > mib[3] = pid;
> > buflen = sizeof buf;
> > if (sysctl (mib, 4, buf, &buflen, NULL, 0) == 0)
> > - return buf;
> > + return buflen == 0 ? NULL : buf;
> > #endif
> >
> > xsnprintf (name, PATH_MAX, "/proc/%d/exe", pid);
> >
>
> LGTM, but maybe add a comment saying in what situation the sysctl can
> return a buflen of 0.
Ok.
> Does the alternative method that reads from /proc/<pid>/exe work in that
> case too?
No. FreeBSD systems don't generally mount /proc (it's not enabled in the
default install), but in the case that 0 is returned, the relevant pointer
in the process structure (p_textvp) that '/proc/%d/exe' returns a path for
is NULL, so the procfs method will also fail.
Actually, I looked at FreeBSD's procfs and the node is named /proc/%d/file,
not /proc/%d/exe. I did confirm that FreeBSD's procfs does not create
'file' nodes for kernel processes (but also not for init (pid 1)).
I should in fact probably refine this function further to only use procfs
in the #else case if not remove it all together: the last release to not
include the pathname sysctl was FreeBSD 5.5 released in May 2006.
--
John Baldwin