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Message-ID: <20140211163629.GM18807@madcap2.tricolour.ca>
Date: Tue, 11 Feb 2014 11:36:29 -0500
From: Richard Guy Briggs <rgb@...hat.com>
To: William Roberts <bill.c.roberts@...il.com>
Cc: linux-audit@...hat.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk,
akpm@...ux-foundation.org, sds@...ho.nsa.gov,
William Roberts <wroberts@...sys.com>
Subject: Re: [PATCH v5 3/3] audit: Audit proc/<pid>/cmdline aka proctitle
On 14/02/06, William Roberts wrote:
> During an audit event, cache and print the value of the process's
> proctitle value (proc/<pid>/cmdline). This is useful in situations
> where processes are started via fork'd virtual machines where the
> comm field is incorrect. Often times, setting the comm field still
> is insufficient as the comm width is not very wide and most
> virtual machine "package names" do not fit. Also, during execution,
> many threads have their comm field set as well. By tying it back to
> the global cmdline value for the process, audit records will be more
> complete in systems with these properties. An example of where this
> is useful and applicable is in the realm of Android. With Android,
> their is no fork/exec for VM instances. The bare, preloaded Dalvik
> VM listens for a fork and specialize request. When this request comes
> in, the VM forks, and the loads the specific application (specializing).
> This was done to take advantage of COW and to not require a load of
> basic packages by the VM on very app spawn. When this spawn occurs,
> the package name is set via setproctitle() and shows up in procfs.
> Many of these package names are longer then 16 bytes, the historical
> width of task->comm. Having the cmdline in the audit records will
> couple the application back to the record directly. Also, on my
> Debian development box, some audit records were more useful then
> what was printed under comm.
>
> The cached proctitle is tied to the life-cycle of the audit_context
> structure and is built on demand.
>
> Proctitle is controllable by userspace, and thus should not be trusted.
> It is meant as an aid to assist in debugging. The proctitle event is
> emitted during syscall audits, and can be filtered with auditctl.
>
> Example:
> type=AVC msg=audit(1391217013.924:386): avc: denied { getattr } for pid=1971 comm="mkdir" name="/" dev="selinuxfs" ino=1 scontext=system_u:system_r:consolekit_t:s0-s0:c0.c255 tcontext=system_u:object_r:security_t:s0 tclass=filesystem
> type=SYSCALL msg=audit(1391217013.924:386): arch=c000003e syscall=137 success=yes exit=0 a0=7f019dfc8bd7 a1=7fffa6aed2c0 a2=fffffffffff4bd25 a3=7fffa6aed050 items=0 ppid=1967 pid=1971 auid=4294967295 uid=0 gid=0 euid=0 suid=0 fsuid=0 egid=0 sgid=0 fsgid=0 tty=(none) ses=4294967295 comm="mkdir" exe="/bin/mkdir" subj=system_u:system_r:consolekit_t:s0-s0:c0.c255 key=(null)
> type=UNKNOWN[1327] msg=audit(1391217013.924:386): proctitle=6D6B646972002D70002F7661722F72756E2F636F6E736F6C65
>
> Signed-off-by: William Roberts <wroberts@...sys.com>
Signed-off-by: Richard Guy Briggs <rgb@...hat.com>
Though, I would prefer to see the size of the proctitle copy buffer
dynamically allocated based on the size of the original rather than
pinned at 128.
> ---
> include/uapi/linux/audit.h | 1 +
> kernel/audit.h | 6 ++++
> kernel/auditsc.c | 67 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 74 insertions(+)
>
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 2d48fe1..4315ee9 100644
> --- a/include/uapi/linux/audit.h
> +++ b/include/uapi/linux/audit.h
> @@ -109,6 +109,7 @@
> #define AUDIT_NETFILTER_PKT 1324 /* Packets traversing netfilter chains */
> #define AUDIT_NETFILTER_CFG 1325 /* Netfilter chain modifications */
> #define AUDIT_SECCOMP 1326 /* Secure Computing event */
> +#define AUDIT_PROCTITLE 1327 /* Proctitle emit event */
>
> #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> diff --git a/kernel/audit.h b/kernel/audit.h
> index 57cc64d..38c967d 100644
> --- a/kernel/audit.h
> +++ b/kernel/audit.h
> @@ -106,6 +106,11 @@ struct audit_names {
> bool should_free;
> };
>
> +struct audit_proctitle {
> + int len; /* length of the cmdline field. */
> + char *value; /* the cmdline field */
> +};
> +
> /* The per-task audit context. */
> struct audit_context {
> int dummy; /* must be the first element */
> @@ -202,6 +207,7 @@ struct audit_context {
> } execve;
> };
> int fds[2];
> + struct audit_proctitle proctitle;
>
> #if AUDIT_DEBUG
> int put_count;
> diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> index 10176cd..e342eb0 100644
> --- a/kernel/auditsc.c
> +++ b/kernel/auditsc.c
> @@ -68,6 +68,7 @@
> #include <linux/capability.h>
> #include <linux/fs_struct.h>
> #include <linux/compat.h>
> +#include <linux/ctype.h>
>
> #include "audit.h"
>
> @@ -79,6 +80,9 @@
> /* no execve audit message should be longer than this (userspace limits) */
> #define MAX_EXECVE_AUDIT_LEN 7500
>
> +/* max length to print of cmdline/proctitle value during audit */
> +#define MAX_PROCTITLE_AUDIT_LEN 128
> +
> /* number of audit rules */
> int audit_n_rules;
>
> @@ -842,6 +846,13 @@ static inline struct audit_context *audit_get_context(struct task_struct *tsk,
> return context;
> }
>
> +static inline void audit_proctitle_free(struct audit_context *context)
> +{
> + kfree(context->proctitle.value);
> + context->proctitle.value = NULL;
> + context->proctitle.len = 0;
> +}
> +
> static inline void audit_free_names(struct audit_context *context)
> {
> struct audit_names *n, *next;
> @@ -955,6 +966,7 @@ static inline void audit_free_context(struct audit_context *context)
> audit_free_aux(context);
> kfree(context->filterkey);
> kfree(context->sockaddr);
> + audit_proctitle_free(context);
> kfree(context);
> }
>
> @@ -1271,6 +1283,59 @@ static void show_special(struct audit_context *context, int *call_panic)
> audit_log_end(ab);
> }
>
> +static inline int audit_proctitle_rtrim(char *proctitle, int len)
> +{
> + char *end = proctitle + len - 1;
> + while (end > proctitle && !isprint(*end))
> + end--;
> +
> + /* catch the case where proctitle is only 1 non-print character */
> + len = end - proctitle + 1;
> + len -= isprint(proctitle[len-1]) == 0;
> + return len;
> +}
> +
> +static void audit_log_proctitle(struct task_struct *tsk,
> + struct audit_context *context)
> +{
> + int res;
> + char *buf;
> + char *msg = "(null)";
> + int len = strlen(msg);
> + struct audit_buffer *ab;
> +
> + ab = audit_log_start(context, GFP_KERNEL, AUDIT_PROCTITLE);
> + if (!ab)
> + return; /* audit_panic or being filtered */
> +
> + audit_log_format(ab, "proctitle=");
> +
> + /* Not cached */
> + if (!context->proctitle.value) {
> + buf = kmalloc(MAX_PROCTITLE_AUDIT_LEN, GFP_KERNEL);
> + if (!buf)
> + goto out;
> + /* Historically called this from procfs naming */
> + res = get_cmdline(tsk, buf, MAX_PROCTITLE_AUDIT_LEN);
> + if (res == 0) {
> + kfree(buf);
> + goto out;
> + }
> + res = audit_proctitle_rtrim(buf, res);
> + if (res == 0) {
> + kfree(buf);
> + goto out;
> + }
> + context->proctitle.value = buf;
> + context->proctitle.len = res;
> + }
> + msg = context->proctitle.value;
> + len = context->proctitle.len;
> +out:
> + audit_log_n_untrustedstring(ab, msg, len);
> + audit_log_end(ab);
> +}
> +
> static void audit_log_exit(struct audit_context *context, struct task_struct *tsk)
> {
> int i, call_panic = 0;
> @@ -1388,6 +1453,8 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
> audit_log_name(context, n, NULL, i++, &call_panic);
> }
>
> + audit_log_proctitle(tsk, context);
> +
> /* Send end of event record to help user space know we are finished */
> ab = audit_log_start(context, GFP_KERNEL, AUDIT_EOE);
> if (ab)
> --
> 1.7.9.5
>
- RGB
--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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