Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753009AbcD1DFJ (ORCPT ); Wed, 27 Apr 2016 23:05:09 -0400 Received: from mail-pf0-f174.google.com ([209.85.192.174]:34369 "EHLO mail-pf0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752632AbcD1DFH (ORCPT ); Wed, 27 Apr 2016 23:05:07 -0400 Subject: Re: [PATCH V4] audit: add tty field to LOGIN event To: Richard Guy Briggs References: <571A5C54.7050704@hurleysoftware.com> <20160428013140.GD18994@madcap2.tricolour.ca> Cc: linux-audit@redhat.com, pmoore@redhat.com, linux-kernel@vger.kernel.org, sgrubb@redhat.com, eparis@redhat.com From: Peter Hurley Message-ID: <57217DDF.5070608@hurleysoftware.com> Date: Wed, 27 Apr 2016 20:05:03 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160428013140.GD18994@madcap2.tricolour.ca> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7491 Lines: 232 On 04/27/2016 06:31 PM, Richard Guy Briggs wrote: > On 16/04/22, Peter Hurley wrote: >> On 04/21/2016 11:14 AM, Richard Guy Briggs wrote: >>> The tty field was missing from AUDIT_LOGIN events. >>> >>> Refactor code to create a new function audit_get_tty(), using it to >>> replace the call in audit_log_task_info() and to add it to >>> audit_log_set_loginuid(). Lock and bump the kref to protect it, adding >>> audit_put_tty() alias to decrement it. >>> >>> Signed-off-by: Richard Guy Briggs >>> --- >>> >>> V4: Add missing prototype for audit_put_tty() when audit syscall is not >>> enabled (MIPS). >>> >>> V3: Introduce audit_put_tty() alias to decrement kref. >>> >>> V2: Use kref to protect tty signal struct while in use. >>> >>> --- >>> >>> include/linux/audit.h | 24 ++++++++++++++++++++++++ >>> kernel/audit.c | 18 +++++------------- >>> kernel/auditsc.c | 8 ++++++-- >>> 3 files changed, 35 insertions(+), 15 deletions(-) >>> >>> diff --git a/include/linux/audit.h b/include/linux/audit.h >>> index b40ed5d..32cdafb 100644 >>> --- a/include/linux/audit.h >>> +++ b/include/linux/audit.h >>> @@ -26,6 +26,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> >>> #define AUDIT_INO_UNSET ((unsigned long)-1) >>> #define AUDIT_DEV_UNSET ((dev_t)-1) >>> @@ -343,6 +344,23 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk) >>> return tsk->sessionid; >>> } >>> >>> +static inline struct tty_struct *audit_get_tty(struct task_struct *tsk) >>> +{ >>> + struct tty_struct *tty = NULL; >>> + unsigned long flags; >>> + >>> + spin_lock_irqsave(&tsk->sighand->siglock, flags); >>> + if (tsk->signal) >>> + tty = tty_kref_get(tsk->signal->tty); >>> + spin_unlock_irqrestore(&tsk->sighand->siglock, flags); >> >> >> Not that I'm objecting because I get that you're just refactoring >> existing code, but I thought I'd point out some stuff. >> >> 1. There's no need to check if signal_struct is NULL (ie. tsk->signal) >> because if it is, this will blow up trying to dereference the >> sighand_struct (ie tsk->sighand). > > Ok. This logic goes back 10 years and one month less two days. (45d9bb0e) > >> 2. The existing usage is always tsk==current > > My understanding is that when it is called via: > > copy_process() > audit_free() > __audit_free() > audit_log_exit() > audit_log_task_info() > > then tsk != current. While it's true that tsk != current here, everything relevant to tty in task_struct is the same because the nascent task is not even half-done. So tsk->sighand == current->sighand, tsk->signal == current->signal etc. If you're uncomfortable with pass-through execution like that, then the simple solution is: struct tty_struct *tty = NULL; /* tsk != current when copy_process() failed */ if (tsk == current) tty = get_current_tty(); because tty_kref_put(tty) accepts NULL tty and (obviously) so does tty_name(tty). Regards, Peter Hurley > This appears to be the only case which appears to > force lugging around tsk. This is noted in that commit referenced > above. > >> 3. If the idea is to make this invulnerable to tsk being gone, then >> the usage is unsafe anyway. >> >> >> So ultimately (but not necessarily for this patch) I'd prefer that either >> a. audit use existing tty api instead of open-coding, or >> b. add any tty api functions required. > > This latter option did cross my mind... > >> Peter Hurley >> >>> + return tty; >>> +} >>> + >>> +static inline void audit_put_tty(struct tty_struct *tty) >>> +{ >>> + tty_kref_put(tty); >>> +} >>> + >>> extern void __audit_ipc_obj(struct kern_ipc_perm *ipcp); >>> extern void __audit_ipc_set_perm(unsigned long qbytes, uid_t uid, gid_t gid, umode_t mode); >>> extern void __audit_bprm(struct linux_binprm *bprm); >>> @@ -500,6 +518,12 @@ static inline unsigned int audit_get_sessionid(struct task_struct *tsk) >>> { >>> return -1; >>> } >>> +static inline struct tty_struct *audit_get_tty(struct task_struct *tsk) >>> +{ >>> + return NULL; >>> +} >>> +static inline void audit_put_tty(struct tty_struct *tty) >>> +{ } >>> static inline void audit_ipc_obj(struct kern_ipc_perm *ipcp) >>> { } >>> static inline void audit_ipc_set_perm(unsigned long qbytes, uid_t uid, >>> diff --git a/kernel/audit.c b/kernel/audit.c >>> index 3a3e5de..7edd776 100644 >>> --- a/kernel/audit.c >>> +++ b/kernel/audit.c >>> @@ -64,7 +64,6 @@ >>> #include >>> #endif >>> #include >>> -#include >>> #include >>> #include >>> >>> @@ -1873,21 +1872,14 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk) >>> { >>> const struct cred *cred; >>> char comm[sizeof(tsk->comm)]; >>> - char *tty; >>> + struct tty_struct *tty; >>> >>> if (!ab) >>> return; >>> >>> /* tsk == current */ >>> cred = current_cred(); >>> - >>> - spin_lock_irq(&tsk->sighand->siglock); >>> - if (tsk->signal && tsk->signal->tty && tsk->signal->tty->name) >>> - tty = tsk->signal->tty->name; >>> - else >>> - tty = "(none)"; >>> - spin_unlock_irq(&tsk->sighand->siglock); >>> - >>> + tty = audit_get_tty(tsk); >>> audit_log_format(ab, >>> " ppid=%d pid=%d auid=%u uid=%u gid=%u" >>> " euid=%u suid=%u fsuid=%u" >>> @@ -1903,11 +1895,11 @@ void audit_log_task_info(struct audit_buffer *ab, struct task_struct *tsk) >>> from_kgid(&init_user_ns, cred->egid), >>> from_kgid(&init_user_ns, cred->sgid), >>> from_kgid(&init_user_ns, cred->fsgid), >>> - tty, audit_get_sessionid(tsk)); >>> - >>> + tty ? tty_name(tty) : "(none)", >>> + audit_get_sessionid(tsk)); >>> + audit_put_tty(tty); >>> audit_log_format(ab, " comm="); >>> audit_log_untrustedstring(ab, get_task_comm(comm, tsk)); >>> - >>> audit_log_d_path_exe(ab, tsk->mm); >>> audit_log_task_context(ab); >>> } >>> diff --git a/kernel/auditsc.c b/kernel/auditsc.c >>> index 195ffae..71e14d8 100644 >>> --- a/kernel/auditsc.c >>> +++ b/kernel/auditsc.c >>> @@ -1980,6 +1980,7 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid, >>> { >>> struct audit_buffer *ab; >>> uid_t uid, oldloginuid, loginuid; >>> + struct tty_struct *tty; >>> >>> if (!audit_enabled) >>> return; >>> @@ -1987,14 +1988,17 @@ static void audit_log_set_loginuid(kuid_t koldloginuid, kuid_t kloginuid, >>> uid = from_kuid(&init_user_ns, task_uid(current)); >>> oldloginuid = from_kuid(&init_user_ns, koldloginuid); >>> loginuid = from_kuid(&init_user_ns, kloginuid), >>> + tty = audit_get_tty(current); >>> >>> ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_LOGIN); >>> if (!ab) >>> return; >>> audit_log_format(ab, "pid=%d uid=%u", task_pid_nr(current), uid); >>> audit_log_task_context(ab); >>> - audit_log_format(ab, " old-auid=%u auid=%u old-ses=%u ses=%u res=%d", >>> - oldloginuid, loginuid, oldsessionid, sessionid, !rc); >>> + audit_log_format(ab, " old-auid=%u auid=%u tty=%s old-ses=%u ses=%u res=%d", >>> + oldloginuid, loginuid, tty ? tty_name(tty) : "(none)", >>> + oldsessionid, sessionid, !rc); >>> + audit_put_tty(tty); >>> audit_log_end(ab); >>> } >>> >>> >> > > - RGB > > -- > Richard Guy Briggs > Kernel Security Engineering, Base Operating Systems, Red Hat > Remote, Ottawa, Canada > Voice: +1.647.777.2635, Internal: (81) 32635 >