Date: Fri, 8 May 2020 19:49:41 +0200 From: Damjan Jovanovic <damjan.jov@gmail.com> To: "Rodney W. Grimes" <freebsd-rwg@gndrsh.dnsmgr.net> Cc: Konstantin Belousov <kib@freebsd.org>, Hackers freeBSD <freebsd-hackers@freebsd.org> Subject: Re: Allow procstat to view current working directory? [xfce4-terminal, linprocfs, ...] Message-ID: <CAJm2B-nRMbgfw1_5nDqurjLSMy-bpnx068SriqJwcn3s9Rd4og@mail.gmail.com> In-Reply-To: <202005081737.048Hb2CA053936@gndrsh.dnsmgr.net> References: <CAJm2B-nShdJ65xy4cvCj-aNj08r_k2L0uHaLcaLAS15mDLbEOQ@mail.gmail.com> <202005081737.048Hb2CA053936@gndrsh.dnsmgr.net>
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On Fri, May 8, 2020 at 7:37 PM Rodney W. Grimes < freebsd-rwg@gndrsh.dnsmgr.net> wrote: > > 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? > > Does that include a path that I should not even be able to see > via file system protections? If so I would classify that as > a data xfiltration security concern. > You're right, on Linux the symlink /proc/1/cwd is there, but the link target is invisible, and "stat cwd" gives: File: 'cwd'stat: cannot read symbolic link 'cwd': Permission denied Size: 0 Blocks: 0 IO Block: 1024 symbolic link Device: 4h/4d Inode: 24821 Links: 1 Access: (0777/lrwxrwxrwx) Uid: ( 0/ root) Gid: ( 0/ root) Access: 2020-05-08 18:10:45.485582443 +0200 Modify: 2020-05-08 18:10:45.441582441 +0200 Change: 2020-05-08 18:10:45.441582441 +0200 Birth: - > > > > > > > > > > > > > > > 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" > > > > > _______________________________________________ > > 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" > > > > -- > Rod Grimes > rgrimes@freebsd.org >
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