Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754843AbZGASdM (ORCPT ); Wed, 1 Jul 2009 14:33:12 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753533AbZGASc7 (ORCPT ); Wed, 1 Jul 2009 14:32:59 -0400 Received: from charlotte.tuxdriver.com ([70.61.120.58]:34167 "EHLO smtp.tuxdriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753934AbZGASc6 (ORCPT ); Wed, 1 Jul 2009 14:32:58 -0400 Date: Wed, 1 Jul 2009 14:32:54 -0400 From: Neil Horman To: linux-kernel@vger.kernel.org Cc: Oleg Nesterov , alan@lxorguk.ukuu.org.uk, andi@firstfloor.org, akpm@linux-foundation.org, earl_chew@agilent.com Subject: Re: [PATCH 2/3] exec: let do_coredump limit the number of concurrent dumps to pipes (v6) Message-ID: <20090701183254.GE31414@hmsreliant.think-freely.org> References: <20090622172818.GB14673@hmsreliant.think-freely.org> <20090701182834.GC31414@hmsreliant.think-freely.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090701182834.GC31414@hmsreliant.think-freely.org> User-Agent: Mutt/1.5.18 (2008-05-17) X-Spam-Score: -1.4 (-) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5844 Lines: 158 core_pattern: Introduce core pipe limiting sysctl Since we can dump cores to pipe, rather than directly to the filesystem, we create a condition in which a user can create a very high load on the system simply by running bad applications. If the pipe reader specified in core_pattern is poorly written, we can have lots of ourstandig resources and processes in the system. This sysctl introduces an ability to limit that resource consumption. core_pipe_limit defines how many in-flight dumps may be run in parallel, dumps beyond this value are skipped and a note is made in the kernel log. A special value of 0 in core_pipe_limit denotes unlimited core dumps may be handled (this is the default value). Signed-off-by: Neil Horman Reported-by: Earl Chew Documentation/sysctl/kernel.txt | 22 ++++++++++++++++++++++ fs/exec.c | 21 +++++++++++++++++---- kernel/sysctl.c | 9 +++++++++ 3 files changed, 48 insertions(+), 4 deletions(-) diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt index 322a00b..bb226ba 100644 --- a/Documentation/sysctl/kernel.txt +++ b/Documentation/sysctl/kernel.txt @@ -21,6 +21,7 @@ show up in /proc/sys/kernel: - acct - auto_msgmni - core_pattern +- core_pipe_limit - core_uses_pid - ctrl-alt-del - dentry-state @@ -119,6 +120,27 @@ core_pattern is used to specify a core dumpfile pattern name. ============================================================== +core_pipe_limit: + +This sysctl is only applicable when core_pattern is configured to pipe core +files to user space helper a (when the first character of core_pattern is a '|', +see above). When collecting cores via a pipe to an application, it is +occasionally usefull for the collecting application to gather data about the +crashing process from its /proc/pid directory. In order to do this safely, the +kernel must wait for the collecting process to exit, so as not to remove the +crashing processes proc files prematurely. This in turn creates the possibility +that a misbehaving userspace collecting process can block the reaping of a +crashed process simply by never exiting. This sysctl defends against that. It +defines how many concurrent crashing processes may be piped to user space +applications in parallel. If this value is exceeded, then those crashing +processes above that value are noted via the kernel log and their cores are +skipped. 0 is a special value, indicating that unlimited processes may be +captured in parallel, but that no waiting will take place (i.e. the collecting +process is not guaranteed access to /proc//). This value defaults +to 0. + +============================================================== + core_uses_pid: The default coredump filename is "core". By setting diff --git a/fs/exec.c b/fs/exec.c index 9defd20..93ab6eb 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -63,6 +63,7 @@ int core_uses_pid; char core_pattern[CORENAME_MAX_SIZE] = "core"; +unsigned int core_pipe_limit; int suid_dumpable = 0; /* The maximal length of core_pattern is also specified in sysctl.c */ @@ -1726,7 +1727,8 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) unsigned long core_limit = current->signal->rlim[RLIMIT_CORE].rlim_cur; char **helper_argv = NULL; int helper_argc = 0; - char *delimit; + int dump_count = 0; + static atomic_t core_dump_count = ATOMIC_INIT(0); audit_core_dumps(signr); @@ -1798,21 +1800,29 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) goto fail_unlock; } + dump_count = atomic_inc_return(&core_dump_count); + if (core_pipe_limit && (core_pipe_limit < dump_count)) { + printk(KERN_WARNING "Pid %d(%s) over core_pipe_limit\n", + task_tgid_vnr(current), current->comm); + printk(KERN_WARNING "Skipping core dump\n"); + goto fail_dropcount; + } + helper_argv = argv_split(GFP_KERNEL, corename+1, &helper_argc); if (!helper_argv) { printk(KERN_WARNING "%s failed to allocate memory\n", __func__); - goto fail_unlock; + goto fail_dropcount; } core_limit = RLIM_INFINITY; /* SIGPIPE can happen, but it's just never processed */ - if (call_usermodehelper_pipe(corename+1, helper_argv, NULL, + if (call_usermodehelper_pipe(helper_argv[0], helper_argv, NULL, &file)) { printk(KERN_INFO "Core dump to %s pipe failed\n", corename); - goto fail_unlock; + goto fail_dropcount; } } else { if (core_limit < binfmt->min_coredump) @@ -1853,6 +1863,9 @@ void do_coredump(long signr, int exit_code, struct pt_regs *regs) close_fail: filp_close(file, NULL); +fail_dropcount: + if (dump_count) + atomic_dec(&core_dump_count); fail_unlock: if (helper_argv) argv_free(helper_argv); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 62e4ff9..681052f 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -77,6 +77,7 @@ extern int max_threads; extern int core_uses_pid; extern int suid_dumpable; extern char core_pattern[]; +extern unsigned int core_pipe_limit; extern int pid_max; extern int min_free_kbytes; extern int pid_max_min, pid_max_max; @@ -407,6 +408,14 @@ static struct ctl_table kern_table[] = { .proc_handler = &proc_dostring, .strategy = &sysctl_string, }, + { + .ctl_name = CTL_UNNUMBERED, + .procname = "core_pipe_limit", + .data = &core_pipe_limit, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = &proc_dointvec, + }, #ifdef CONFIG_PROC_SYSCTL { .procname = "tainted", -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/