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

From: Richard Guy Briggs
Date: Tue Feb 11 2014 - 13:57:07 EST

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In reply to: William Roberts: "Re: [PATCH v5 3/3] audit: Audit proc/<pid>/cmdline aka proctitle"
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On 14/02/11, William Roberts wrote:
> 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.

This could be clamped at PAGE_SIZE.

> >> ---
> >> 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

- 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
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Next message: Richard Guy Briggs: "Re: [PATCH v7 3/3] audit: Audit proc/<pid>/cmdline aka proctitle"
Previous message: Stefano Stabellini: "Re: [PATCH v8] xen/grant-table: Avoid m2p_override during mapping"
In reply to: William Roberts: "Re: [PATCH v5 3/3] audit: Audit proc/<pid>/cmdline aka proctitle"
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