Date: Fri, 8 May 2020 17:57:24 +0200 From: Damjan Jovanovic <damjan.jov@gmail.com> To: Konstantin Belousov <kib@freebsd.org> Cc: Hackers freeBSD <freebsd-hackers@freebsd.org> Subject: Re: Allow procstat to view current working directory? [xfce4-terminal, linprocfs, ...] Message-ID: <CAJm2B-nShdJ65xy4cvCj-aNj08r_k2L0uHaLcaLAS15mDLbEOQ@mail.gmail.com> In-Reply-To: <20200506214611.GD3866@kib.kiev.ua> References: <CAJm2B-=ja7u30xhVbT_8EX96ieBm%2BkqfTaT=1qfBD2B%2BZ9cCWg@mail.gmail.com> <20200506214611.GD3866@kib.kiev.ua>
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On Wed, May 6, 2020 at 11:46 PM Konstantin Belousov <kib@freebsd.org> wrote: > On Wed, May 06, 2020 at 08:32:08PM +0200, Damjan Jovanovic wrote: > > Hi > > > > Currently "procstat fd [pid]" cannot view anything, even for other > > processes owned by the user making the call, not even their current > working > > directory (CWD), unless it has PGET_CANDEBUG permission. > > > > linprocfs however allows reading the CWD for any process because it > doesn't > > perform that check (sys/compat/linprocfs/linprocfs.c, function > > linprocfs_doproccwd()). > > > > Applications use this, eg. xfce4-terminal relies on > > /compat/linux/proc/<pid>/cwd to find the shell's CWD, so that when you > open > > a new tab, it starts in the same CWD as the tab you opened it from ( > > > https://github.com/xfce-mirror/xfce4-terminal/blob/master/terminal/terminal-screen.c#L2343 > ). > > I would like to patch xfce4-terminal to use libprocstat for that instead > of > > needing linprocfs to be mounted, but since procstat is more restrictive, > it > > will break it. > > > > Can we please downgrade PGET_CANDEBUG to at least PGET_CANSEE, so you can > > view the CWD for processes you own? Maybe other open files still need to > be > > hidden, but the CWD doesn't seem like a major security concern. > Can you explain why CANDEBUG vs CANSEE matters for your case ? > Or better, why xfce4-terminal cannot debug shells it spawns ? > Is it suid ? > > xfce4-terminal is a normal process, no suid. It wants to read CWD of the current tab so the new tab opens in the same directory, which is often what you want. On Linux /proc/<pid>/cwd is lrwxrwxrwx for all processes. On FreeBSD /compat/linux/proc/<pid>/cwd is lrwxrwxrwx for all procesess. It works as intended at present, as long as you have linprocfs mounted. But I'd rather not have to mount linprocfs. If I patch xfce4-terminal to use libprocstat instead, then it will break, as it needs CANDEBUG to see the CWD, a restriction that seems extreme. > > My initial reaction was that linprocfs should be patched to match FreeBSD > native behaviour instead. > Why does Linux allow everyone to see CWD for all processes? > > > > > Linux's own /proc filesystem never hides the CWD (lrwxrwxrwx), and only > > hides file descriptors for processes you don't own. > > > > A patch along the following lines could be a start: > > > > diff --git a/sys/kern/kern_descrip.c b/sys/kern/kern_descrip.c > > index 423968b2e1cc..f487232d2cff 100644 > > --- a/sys/kern/kern_descrip.c > > +++ b/sys/kern/kern_descrip.c > > @@ -3692,7 +3692,7 @@ sysctl_kern_proc_filedesc(SYSCTL_HANDLER_ARGS) > > > > sbuf_new_for_sysctl(&sb, NULL, FILEDESC_SBUF_SIZE, req); > > sbuf_clear_flags(&sb, SBUF_INCLUDENUL); > > - error = pget((pid_t)name[0], PGET_CANDEBUG | PGET_NOTWEXIT, &p); > > + error = pget((pid_t)name[0], PGET_CANSEE | PGET_NOTWEXIT, &p); > > if (error != 0) { > > sbuf_delete(&sb); > > return (error); > > @@ -3768,7 +3768,7 @@ sysctl_kern_proc_ofiledesc(SYSCTL_HANDLER_ARGS) > > struct proc *p; > > > > name = (int *)arg1; > > - error = pget((pid_t)name[0], PGET_CANDEBUG | PGET_NOTWEXIT, &p); > > + error = pget((pid_t)name[0], PGET_CANSEE | PGET_NOTWEXIT, &p); > > if (error != 0) > > return (error); > > fdp = fdhold(p); > > > > > > > > > > Thank you > > Damjan > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > https://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to " > freebsd-hackers-unsubscribe@freebsd.org" >
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