From patchwork Thu Jun 19 13:19:36 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Thompson X-Patchwork-Id: 32223 Return-Path: X-Original-To: linaro@patches.linaro.org Delivered-To: linaro@patches.linaro.org Received: from mail-ve0-f197.google.com (mail-ve0-f197.google.com [209.85.128.197]) by ip-10-151-82-157.ec2.internal (Postfix) with ESMTPS id 78BD7206A0 for ; Thu, 19 Jun 2014 13:20:21 +0000 (UTC) Received: by mail-ve0-f197.google.com with SMTP id jz11sf7487754veb.8 for ; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:delivered-to:from:to:cc:subject :date:message-id:in-reply-to:references:x-original-sender :x-original-authentication-results:precedence:mailing-list:list-id :list-post:list-help:list-archive:list-unsubscribe; bh=PYdIQc1cIxN9yHOsOUUukEpHlan2V4H10HrHvtwyMkc=; b=j8RmwvHxeeWNkTHKPfB3WpppPzEbuuDGkZ8nYmvUO8Ns4hWlcWTlcDRkSk3+RbQ/7I giWwvkQDeT8wO/POfjHBjkJ6m0DuYTEt51BUEsaPn1bAmRMKOL0LT4NV6Bb3D8ZJ38yc Xh/874mk3lq511dumbVFLwq0xAoRjZg0/uMR8NUM6l6D/N9JmweU+8rQtkLME25ZaTQK H1ekWHR8c94w1XXlsk1tSoOd0GdqgdbzfXD4n7T6G9GXdy+iLBj+JhYFAixAuJjiJcfU 8IaGA4JEv+BXfVW9BYUOwznlT5RS5heagLtNjRakpQgv95XUQHh0v9jXkvpyHWb4PAXe 3JYg== X-Gm-Message-State: ALoCoQn4ymwNUNVem2oc2CVycYjlT/xa8j+UiuX/4Hba8tMylv8lCbyZi7fwnfoXodwaU46m1ctR X-Received: by 10.58.199.135 with SMTP id jk7mr2312398vec.22.1403184021302; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) MIME-Version: 1.0 X-BeenThere: patchwork-forward@linaro.org Received: by 10.140.92.68 with SMTP id a62ls516308qge.79.gmail; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) X-Received: by 10.220.103.141 with SMTP id k13mr3875747vco.25.1403184021205; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) Received: from mail-ve0-f173.google.com (mail-ve0-f173.google.com [209.85.128.173]) by mx.google.com with ESMTPS id o6si2358245vek.62.2014.06.19.06.20.21 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 19 Jun 2014 06:20:21 -0700 (PDT) Received-SPF: pass (google.com: domain of patch+caf_=patchwork-forward=linaro.org@linaro.org designates 209.85.128.173 as permitted sender) client-ip=209.85.128.173; Received: by mail-ve0-f173.google.com with SMTP id db11so2269278veb.18 for ; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) X-Received: by 10.58.216.163 with SMTP id or3mr175299vec.80.1403184021124; Thu, 19 Jun 2014 06:20:21 -0700 (PDT) X-Forwarded-To: patchwork-forward@linaro.org X-Forwarded-For: patch@linaro.org patchwork-forward@linaro.org Delivered-To: patches@linaro.org Received: by 10.221.54.6 with SMTP id vs6csp361298vcb; Thu, 19 Jun 2014 06:20:20 -0700 (PDT) X-Received: by 10.58.72.165 with SMTP id e5mr286255vev.59.1403184020728; Thu, 19 Jun 2014 06:20:20 -0700 (PDT) Received: from mail-we0-f182.google.com (mail-we0-f182.google.com [74.125.82.182]) by mx.google.com with ESMTPS id v8si7206845wjq.85.2014.06.19.06.20.19 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Thu, 19 Jun 2014 06:20:20 -0700 (PDT) Received-SPF: pass (google.com: domain of daniel.thompson@linaro.org designates 74.125.82.182 as permitted sender) client-ip=74.125.82.182; Received: by mail-we0-f182.google.com with SMTP id q59so2366602wes.27 for ; Thu, 19 Jun 2014 06:20:19 -0700 (PDT) X-Received: by 10.194.238.231 with SMTP id vn7mr4689103wjc.99.1403184019396; Thu, 19 Jun 2014 06:20:19 -0700 (PDT) Received: from sundance.lan (cpc4-aztw19-0-0-cust157.18-1.cable.virginm.net. [82.33.25.158]) by mx.google.com with ESMTPSA id m3sm11538652wik.7.2014.06.19.06.20.17 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 19 Jun 2014 06:20:18 -0700 (PDT) From: Daniel Thompson To: kgdb-bugreport@lists.sourceforge.net, Jason Wessel Cc: Anton Vorontsov , patches@linaro.org, linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Jiri Slaby , Steven Rostedt , Frederic Weisbecker , Ingo Molnar , John Stultz , Colin Cross , kernel-team@android.com, Daniel Thompson Subject: [PATCH v5 7/8] kdb: Add enable mask for groups of commands Date: Thu, 19 Jun 2014 14:19:36 +0100 Message-Id: <1403183977-3454-8-git-send-email-daniel.thompson@linaro.org> X-Mailer: git-send-email 1.9.3 In-Reply-To: <1403183977-3454-1-git-send-email-daniel.thompson@linaro.org> References: <1399381429-16194-1-git-send-email-daniel.thompson@linaro.org> <1403183977-3454-1-git-send-email-daniel.thompson@linaro.org> X-Removed-Original-Auth: Dkim didn't pass. X-Original-Sender: daniel.thompson@linaro.org X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of patch+caf_=patchwork-forward=linaro.org@linaro.org designates 209.85.128.173 as permitted sender) smtp.mail=patch+caf_=patchwork-forward=linaro.org@linaro.org Precedence: list Mailing-list: list patchwork-forward@linaro.org; contact patchwork-forward+owners@linaro.org List-ID: X-Google-Group-Id: 836684582541 List-Post: , List-Help: , List-Archive: List-Unsubscribe: , From: Anton Vorontsov Currently all kdb commands are enabled whenever kdb is deployed. This makes it difficult to deploy kdb to help debug certain types of systems. Android phones provide one example; the FIQ debugger found on some Android devices has a deliberately weak set of commands to allow the debugger to enabled very late in the production cycle. Certain kiosk environments offer another interesting case where an engineer might wish to probe the system state using passive inspection commands without providing sufficient power for a passer by to root it. Without any restrictions, obtaining the root rights via KDB is a matter of a few commands, and works everywhere. For example, log in as a normal user: cbou:~$ id uid=1001(cbou) gid=1001(cbou) groups=1001(cbou) Now enter KDB (for example via sysrq): Entering kdb (current=0xffff8800065bc740, pid 920) due to Keyboard Entry kdb> ps 23 sleeping system daemon (state M) processes suppressed, use 'ps A' to see all. Task Addr Pid Parent [*] cpu State Thread Command 0xffff8800065bc740 920 919 1 0 R 0xffff8800065bca20 *bash 0xffff880007078000 1 0 0 0 S 0xffff8800070782e0 init [...snip...] 0xffff8800065be3c0 918 1 0 0 S 0xffff8800065be6a0 getty 0xffff8800065b9c80 919 1 0 0 S 0xffff8800065b9f60 login 0xffff8800065bc740 920 919 1 0 R 0xffff8800065bca20 *bash All we need is the offset of cred pointers. We can look up the offset in the distro's kernel source, but it is unnecessary. We can just start dumping init's task_struct, until we see the process name: kdb> md 0xffff880007078000 0xffff880007078000 0000000000000001 ffff88000703c000 ................ 0xffff880007078010 0040210000000002 0000000000000000 .....!@......... [...snip...] 0xffff8800070782b0 ffff8800073e0580 ffff8800073e0580 ..>.......>..... 0xffff8800070782c0 0000000074696e69 0000000000000000 init............ ^ Here, 'init'. Creds are just above it, so the offset is 0x02b0. Now we set up init's creds for our non-privileged shell: kdb> mm 0xffff8800065bc740+0x02b0 0xffff8800073e0580 0xffff8800065bc9f0 = 0xffff8800073e0580 kdb> mm 0xffff8800065bc740+0x02b8 0xffff8800073e0580 0xffff8800065bc9f8 = 0xffff8800073e0580 And thus gaining the root: kdb> go cbou:~$ id uid=0(root) gid=0(root) groups=0(root) cbou:~$ bash root:~# p.s. No distro enables kdb by default (although, with a nice KDB-over-KMS feature availability, I would expect at least some would enable it), so it's not actually some kind of a major issue. Signed-off-by: Anton Vorontsov Signed-off-by: John Stultz Signed-off-by: Daniel Thompson Cc: Jason Wessel Cc: kgdb-bugreport@lists.sourceforge.net --- include/linux/kdb.h | 1 + kernel/debug/kdb/kdb_main.c | 30 +++++++++++++++++++++++++++++- 2 files changed, 30 insertions(+), 1 deletion(-) diff --git a/include/linux/kdb.h b/include/linux/kdb.h index f1fe361..75ae2e2 100644 --- a/include/linux/kdb.h +++ b/include/linux/kdb.h @@ -105,6 +105,7 @@ extern atomic_t kdb_event; #define KDB_BADLENGTH (-19) #define KDB_NOBP (-20) #define KDB_BADADDR (-21) +#define KDB_NOPERM (-22) /* * kdb_diemsg diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c index 941ff97..c670fe4 100644 --- a/kernel/debug/kdb/kdb_main.c +++ b/kernel/debug/kdb/kdb_main.c @@ -12,6 +12,7 @@ */ #include +#include #include #include #include @@ -23,6 +24,7 @@ #include #include #include +#include #include #include #include @@ -42,6 +44,12 @@ #include #include "kdb_private.h" +#undef MODULE_PARAM_PREFIX +#define MODULE_PARAM_PREFIX "kdb." + +static int kdb_cmd_enabled; +module_param_named(cmd_enable, kdb_cmd_enabled, int, 0600); + #define GREP_LEN 256 char kdb_grep_string[GREP_LEN]; int kdb_grepping_flag; @@ -121,6 +129,7 @@ static kdbmsg_t kdbmsgs[] = { KDBMSG(BADLENGTH, "Invalid length field"), KDBMSG(NOBP, "No Breakpoint exists"), KDBMSG(BADADDR, "Invalid address"), + KDBMSG(NOPERM, "Permission denied"), }; #undef KDBMSG @@ -496,6 +505,15 @@ int kdbgetaddrarg(int argc, const char **argv, int *nextarg, kdb_symtab_t symtab; /* + * If the enable flags prohibit both arbitrary memory access + * and flow control then there are no reasonable grounds to + * provide symbol lookup. + */ + if (!kdb_check_flags(KDB_ENABLE_MEM_READ | KDB_ENABLE_FLOW_CTRL, + kdb_cmd_enabled, false)) + return KDB_NOPERM; + + /* * Process arguments which follow the following syntax: * * symbol | numeric-address [+/- numeric-offset] @@ -1028,6 +1046,10 @@ int kdb_parse(const char *cmdstr) if (i < kdb_max_commands) { int result; + + if (!kdb_check_flags(tp->cmd_flags, kdb_cmd_enabled, argc <= 1)) + return KDB_NOPERM; + KDB_STATE_SET(CMD); result = (*tp->cmd_func)(argc-1, (const char **)argv); if (result && ignore_errors && result > KDB_CMD_GO) @@ -1939,10 +1961,14 @@ static int kdb_rm(int argc, const char **argv) */ static int kdb_sr(int argc, const char **argv) { + bool check_mask = + !kdb_check_flags(KDB_ENABLE_ALL, kdb_cmd_enabled, false); + if (argc != 1) return KDB_ARGCOUNT; + kdb_trap_printk++; - __handle_sysrq(*argv[1], false); + __handle_sysrq(*argv[1], check_mask); kdb_trap_printk--; return 0; @@ -2393,6 +2419,8 @@ static int kdb_help(int argc, const char **argv) return 0; if (!kt->cmd_name) continue; + if (!kdb_check_flags(kt->cmd_flags, kdb_cmd_enabled, true)) + continue; if (strlen(kt->cmd_usage) > 20) space = "\n "; kdb_printf("%-15.15s %-20s%s%s\n", kt->cmd_name,