From patchwork Tue Oct 16 01:18:05 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anton Vorontsov X-Patchwork-Id: 12261 Return-Path: X-Original-To: patchwork@peony.canonical.com Delivered-To: patchwork@peony.canonical.com Received: from fiordland.canonical.com (fiordland.canonical.com [91.189.94.145]) by peony.canonical.com (Postfix) with ESMTP id 81B9523E29 for ; Tue, 16 Oct 2012 01:21:27 +0000 (UTC) Received: from mail-ie0-f180.google.com (mail-ie0-f180.google.com [209.85.223.180]) by fiordland.canonical.com (Postfix) with ESMTP id 3A7B1A1914F for ; Tue, 16 Oct 2012 01:21:27 +0000 (UTC) Received: by mail-ie0-f180.google.com with SMTP id e10so8690275iej.11 for ; Mon, 15 Oct 2012 18:21:27 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=x-forwarded-to:x-forwarded-for:delivered-to:received-spf:from:to:cc :subject:date:message-id:x-mailer:in-reply-to:references :x-gm-message-state; bh=N3Tsol8fhKTaqy/S0kdNNOTFnhT533w62Uow2BLfoYc=; b=eXRPVX+waPJmg1T2uN1ABCkTwu6GtZxLTs/5TMfCyBNOGOAYkRsI0luX6C1sEUi06m 1xk/HSREdiKimIoDReu9jD8OKW+DXKl4KteKlviIcbeAMdyvVZHwXDeNkTAJBF0y5qt2 gXNNrmAJOlQYZXyYV7/noxUhx0n6yePNpnEfMYZSmcdF9XQld5B5nExFU9cLPEv/xC4Z aUEgizhHGZdHPB3DgQTD3MyMnI3pjpfNiH+MFi1MogS7y7WgknRQWTsFXhUYs6xMKM+E c7RmBSVjWZ5XUhJa6KB9kU0vQXW+TLxr68Y9EG41I2xTzuwAcf4N+7h9TQUFHsTthz1+ k3qA== Received: by 10.50.100.137 with SMTP id ey9mr10485207igb.57.1350350486974; Mon, 15 Oct 2012 18:21:26 -0700 (PDT) X-Forwarded-To: linaro-patchwork@canonical.com X-Forwarded-For: patch@linaro.org linaro-patchwork@canonical.com Delivered-To: patches@linaro.org Received: by 10.50.67.148 with SMTP id n20csp659675igt; Mon, 15 Oct 2012 18:21:26 -0700 (PDT) Received: by 10.68.229.138 with SMTP id sq10mr42519124pbc.126.1350350486304; Mon, 15 Oct 2012 18:21:26 -0700 (PDT) Received: from mail-pb0-f50.google.com (mail-pb0-f50.google.com [209.85.160.50]) by mx.google.com with ESMTPS id i9si24189886pay.314.2012.10.15.18.21.26 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 15 Oct 2012 18:21:26 -0700 (PDT) Received-SPF: neutral (google.com: 209.85.160.50 is neither permitted nor denied by best guess record for domain of anton.vorontsov@linaro.org) client-ip=209.85.160.50; Authentication-Results: mx.google.com; spf=neutral (google.com: 209.85.160.50 is neither permitted nor denied by best guess record for domain of anton.vorontsov@linaro.org) smtp.mail=anton.vorontsov@linaro.org Received: by mail-pb0-f50.google.com with SMTP id md4so6058032pbc.37 for ; Mon, 15 Oct 2012 18:21:26 -0700 (PDT) Received: by 10.66.79.195 with SMTP id l3mr37352815pax.33.1350350486082; Mon, 15 Oct 2012 18:21:26 -0700 (PDT) Received: from localhost (ip-64-134-230-8.public.wayport.net. [64.134.230.8]) by mx.google.com with ESMTPS id pl2sm4374957pbb.66.2012.10.15.18.21.25 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 15 Oct 2012 18:21:25 -0700 (PDT) From: Anton Vorontsov To: Jason Wessel Cc: Colin Cross , Alan Cox , John Stultz , linux-kernel@vger.kernel.org, linaro-kernel@lists.linaro.org, patches@linaro.org, kernel-team@android.com, kgdb-bugreport@lists.sourceforge.net Subject: [PATCH 7/7] kdb: Add kiosk mode Date: Mon, 15 Oct 2012 18:18:05 -0700 Message-Id: <1350350285-3095-7-git-send-email-anton.vorontsov@linaro.org> X-Mailer: git-send-email 1.7.12.3 In-Reply-To: <20121016011724.GB23146@lizard> References: <20121016011724.GB23146@lizard> X-Gm-Message-State: ALoCoQkccxUB/wrXBZzjswdAwHlUcwhWN/ilAJpkLkosowlUH7agbMk/lsuUFtAwXirq6CT9Qyjr By issuing 'echo 1 > /sys/module/kdb/parameters/kiosk' or booting with kdb.kiosk=1 kernel command line option, one can still have a somewhat usable debugging facility, but not fearing that the debugger can be used to easily gain root access or dump sensitive data. Without the kiosk mode, 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 --- include/linux/kdb.h | 1 + kernel/debug/kdb/kdb_main.c | 20 +++++++++++++++++++- 2 files changed, 20 insertions(+), 1 deletion(-) diff --git a/include/linux/kdb.h b/include/linux/kdb.h index abe927c..3a2c554 100644 --- a/include/linux/kdb.h +++ b/include/linux/kdb.h @@ -63,6 +63,7 @@ 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 83c3f60..36e4c2a 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 bool kdb_kiosk; +module_param_named(kiosk, kdb_kiosk, bool, 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 @@ -987,6 +996,14 @@ int kdb_parse(const char *cmdstr) if (i < kdb_max_commands) { int result; + + if (kdb_kiosk) { + if (!(tp->cmd_flags & (KDB_SAFE | KDB_SAFE_NO_ARGS))) + return KDB_NOPERM; + if (tp->cmd_flags & KDB_SAFE_NO_ARGS && 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) @@ -1009,7 +1026,7 @@ int kdb_parse(const char *cmdstr) * obtaining the address of a variable, or the nearest symbol * to an address contained in a register. */ - { + if (!kdb_kiosk) { unsigned long value; char *name = NULL; long offset; @@ -1025,6 +1042,7 @@ int kdb_parse(const char *cmdstr) kdb_printf("\n"); return 0; } + return KDB_NOPERM; }