Re: [PATCH v5 3/3] audit: Audit proc/<pid>/cmdline aka proctitle

From: William Roberts
Date: Tue Feb 11 2014 - 12:25:56 EST

On Tue, Feb 11, 2014 at 8:36 AM, Richard Guy Briggs <rgb@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
>
> Signed-off-by: Richard Guy Briggs <rgb@xxxxxxxxxx>
>
> 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.

Not as good as it originally seems as this could be a whole page,
which would result in 2*PAGE_SIZE if hex escaped back to
userspace. A tuneable interface could be added in the future if its needed.

>
>> ---
>> 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@xxxxxxxxxx>
> 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



--
Respectfully,

William C Roberts
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