From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932501AbYDYSNk (ORCPT ); Fri, 25 Apr 2008 14:13:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1762628AbYDYSNY (ORCPT ); Fri, 25 Apr 2008 14:13:24 -0400 Received: from wa-out-1112.google.com ([209.85.146.176]:31204 "EHLO wa-out-1112.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759688AbYDYSNW (ORCPT ); Fri, 25 Apr 2008 14:13:22 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=googlemail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version:content-type:content-transfer-encoding:content-disposition:references; b=oRcwg99GHN1lLX3dDQaaIzFpn/Gh8VGgJW2Xh4cYM5w+o8Lt5ikyIZbaURgPN7BRvXDkReYQAchZcAYtxcA3CsSxVoL2cmCT1Qin+E+YO9mBfc1QyDAV8oXdMaU3lncUF/ipYLv1cqhm7FZ83n95gV4p7vwmus7Gcdv/G3oAHhI= Message-ID: Date: Fri, 25 Apr 2008 20:13:21 +0200 From: "Michael Kerrisk" To: "Neil Horman" Subject: Re: core_pattern pipe documentation Cc: "Andi Kleen" , linux-man@vger.kernel.org, "Linux Kernel Mailing List" , "Petr Gajdos" , michael.kerrisk@gmail.com In-Reply-To: <20080425162225.GA9833@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <48051FBA.60503@firstfloor.org> <4808D1F4.7050705@gmail.com> <20080423145933.GA26228@hmsendeavour.rdu.redhat.com> <20080425162225.GA9833@hmsreliant.think-freely.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 25, 2008 at 6:22 PM, Neil Horman wrote: > > On Fri, Apr 25, 2008 at 03:18:46PM +0200, Michael Kerrisk wrote: > > Hi Neil, > > > > On Wed, Apr 23, 2008 at 4:59 PM, Neil Horman wrote: > > > > > > On Wed, Apr 23, 2008 at 02:09:14PM +0200, Michael Kerrisk wrote: > > > > Andi -- ping! > > > > > > > > Adding Neil to CC, since it looks like he also did some work here, and > > > > so can perhaps comment. > > > > > > > > On Fri, Apr 18, 2008 at 6:53 PM, Michael Kerrisk > > > > wrote: > > > > > Andi, > > > > > > > > > > I wrote the following description of the core_pattern pipe feature. Does this > > > > > seem okay? > > > > > > > > > > Piping core dumps to a program > > > > > Since kernel 2.6.19, Linux supports an alternate syntax > > > > > for the /proc/sys/kernel/core_pattern file. If the first > > > > > character of this file is a pipe symbol (|), then the > > > > > remainder of the line is interpreted as a program to be > > > > > executed. Instead of being written to a disk file, the > > > > > core dump is given as standard input to the program. > > > > > Note the following points: > > > > > > > > > > * The program must be specified using an absolute path- > > > > > name (or a pathname relative to the root directory, > > > > > /), and must immediately follow the '|' character. > > > > > > > > > > * The process created to run the program runs as user > > > > > and group root. > > > > > > > > > > * Arguments can be supplied to the program, delimited by > > > > > white space (up to a total line length of 128 bytes). > > > > > > > > > > Cheers, > > > > > > > > > > Michael > > > > > > > > Thanks for CC'ing me. The above all looks good. I would add documentation > > > however, about the available macros that can be used when core_pattern is > > > specified as a pipe. Adding something like the following would be good: > > > > > > * Arguments can be statically declared or implied via the use of macros, > > > denoted by the use of the %sign. The following macros are supported: > > > * %% - output a literal % sign on the command line > > > * %p - the pid of the crashing process > > > * %u - the uid of the crashing process > > > * %g - the gid of the crashing process > > > * %s - the signal that caused the crashing process to crash > > > * %t - the time the crashing process dumped > > > * %h - the hostname of the system > > > * %e - the executable name of the crashing process > > > * %c - the core limit size of the crashing process > > > > Thanks for pointing that out! I'll note it in the page. > > > > > Note that the core limit size macro may be a different value than what > > > is returned by getrlimit(RLIMIT_CORE,...). This is due to the fact > > > that the core_pattern specified executible will be run as the same uid > > > as the crashing process, and to facilitate reception of the entire > > > core, the kernel will temporarily set RLIMIT_CORE to unlimited while > > > the dump is in progress. > > > > Actually, I can't seem to get an example of this behavior. In my > > experiments, %c always seems to give the "right" info (i.e., I don't > > ever see %c showing 2^32 (unlimited) when I set a soft limit). Can > > you show a specific case where it doesn't give the "right" value? > > > Oops, you're right. I had initially implemented my core pattern updates this > way, but in the end wound up just ignoring the limit in do_coredump, rather than > re-writing it. Thanks for that. You can scratch this. > > > > > Note also %u and %g may be different values > > > than getuid/getgid in the event that the core_pattern executable is > > > set[u|g]id root > > > > I'm slightly confused by that last point. According to my > > experiments, the core_pattern executable is always run as user and > > group root, so making it set[ug]id root would seem to be a no-op. > > (But anyway, %u and %g do give the "right" values -- the UID and GID > > of the dumping process.) > > > Hmm, are you sure, I was under the impression that we fork the usermodehelper in > do_coredump as a parent of current, which has the dumping processes uid/gid. I > do see that in do_coredump we call get_dumpable(mm) and if it returns with the > appropriate value we switch current->fsuid to 0. I wonder if thats what you're > seeing? Have a look at the following. It demonstrates what I'm seeing (that the coredump program is run as root/root). === $ cat core_pattern_test.c /* core_pattern_test.c */ #define _GNU_SOURCE #include #include #include #include #include #define BUF_SIZE 1024 int main(int argc, char *argv[]) { int fd, tot, j; ssize_t nread; char buf[BUF_SIZE]; FILE *fp; fd = open(argv[1], O_CREAT | O_WRONLY | O_TRUNC, 0666); if (fd == -1) exit(EXIT_FAILURE); fp = fdopen(fd, "a"); fprintf(fp, "PID=%ld\n", (long) getpid()); fprintf(fp, "cwd=%s\n", get_current_dir_name()); fprintf(fp, "UID=%ld; EUID=%ld\n", (long) getuid(), (long) geteuid()); fprintf(fp, "GID=%ld; EGID=%ld\n", (long) getgid(), (long) getegid()); fprintf(fp, "argc=%d\n", argc); for (j = 0; j < argc; j++) fprintf(fp, "argc[%d]=<%s>\n", j, argv[j]); /* Count bytes in standard input */ tot = 0; while ((nread = read(STDIN_FILENO, buf, BUF_SIZE)) > 0) tot += nread; fprintf(fp, "Total bytes in core dump: %d\n", tot); exit(EXIT_SUCCESS); } $ cc core_pattern_test.c $ sudo sh -c 'echo "|$PWD/core_pattern_test $PWD/c p_%p u_%u g_%g t_%t c_%c" > /proc/sys/kernel/core_pattern' root's password: $ id uid=1000(mtk) gid=100(users) groups=16(dialout),33(video),100(users) $ sleep 100 [type ^\] Quit (core dumped) $ cat c PID=6743 cwd=/ UID=0; EUID=0 GID=0; EGID=0 argc=7 argc[0]= argc[1]= argc[2]= argc[3]= argc[4]= argc[5]= argc[6]= Total bytes in core dump: 282624 $ === Your thoughts? Cheers, Michael