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[PATCH] add rule filterkey
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Add support for a rule key, which can be used to tie audit records to audit
rules.  This is useful when a watched file is accessed through a link or
symlink, as well as for general audit log analysis.

Because this patch uses a string key instead of an integer key, there is a bit
of extra overhead to do the kstrdup() when a rule fires.  However, we're also
allocating memory for the audit record buffer, so it's probably not that
significant.  I went ahead with a string key because it seems more
user-friendly.

Note that the user must ensure that filterkeys are unique.  The kernel only
checks for duplicate rules.

Signed-off-by: Amy Griffis <[email protected]>
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Amy Griffis authored and Al Viro committed Jul 1, 2006
1 parent 9262e91 commit 5adc8a6
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Showing 4 changed files with 78 additions and 36 deletions.
3 changes: 3 additions & 0 deletions include/linux/audit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,7 @@
/* Rule structure sizes -- if these change, different AUDIT_ADD and
* AUDIT_LIST commands must be implemented. */
#define AUDIT_MAX_FIELDS 64
#define AUDIT_MAX_KEY_LEN 32
#define AUDIT_BITMASK_SIZE 64
#define AUDIT_WORD(nr) ((__u32)((nr)/32))
#define AUDIT_BIT(nr) (1 << ((nr) - AUDIT_WORD(nr)*32))
Expand Down Expand Up @@ -171,6 +172,8 @@
#define AUDIT_ARG2 (AUDIT_ARG0+2)
#define AUDIT_ARG3 (AUDIT_ARG0+3)

#define AUDIT_FILTERKEY 210

#define AUDIT_NEGATE 0x80000000

/* These are the supported operators.
Expand Down
1 change: 1 addition & 0 deletions kernel/audit.h
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Original file line number Diff line number Diff line change
Expand Up @@ -81,6 +81,7 @@ struct audit_krule {
u32 mask[AUDIT_BITMASK_SIZE];
u32 buflen; /* for data alloc on list rules */
u32 field_count;
char *filterkey; /* ties events to rules */
struct audit_field *fields;
struct audit_field *inode_f; /* quick access to an inode field */
struct audit_watch *watch; /* associated watch */
Expand Down
95 changes: 59 additions & 36 deletions kernel/auditfilter.c
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,7 @@ static inline void audit_free_rule(struct audit_entry *e)
selinux_audit_rule_free(f->se_rule);
}
kfree(e->rule.fields);
kfree(e->rule.filterkey);
kfree(e);
}

Expand Down Expand Up @@ -511,6 +512,16 @@ static struct audit_entry *audit_data_to_entry(struct audit_rule_data *data,
if (err)
goto exit_free;
break;
case AUDIT_FILTERKEY:
err = -EINVAL;
if (entry->rule.filterkey || f->val > AUDIT_MAX_KEY_LEN)
goto exit_free;
str = audit_unpack_string(&bufp, &remain, f->val);
if (IS_ERR(str))
goto exit_free;
entry->rule.buflen += f->val;
entry->rule.filterkey = str;
break;
default:
goto exit_free;
}
Expand Down Expand Up @@ -612,6 +623,10 @@ static struct audit_rule_data *audit_krule_to_data(struct audit_krule *krule)
data->buflen += data->values[i] =
audit_pack_string(&bufp, krule->watch->path);
break;
case AUDIT_FILTERKEY:
data->buflen += data->values[i] =
audit_pack_string(&bufp, krule->filterkey);
break;
default:
data->values[i] = f->val;
}
Expand Down Expand Up @@ -651,6 +666,11 @@ static int audit_compare_rule(struct audit_krule *a, struct audit_krule *b)
if (strcmp(a->watch->path, b->watch->path))
return 1;
break;
case AUDIT_FILTERKEY:
/* both filterkeys exist based on above type compare */
if (strcmp(a->filterkey, b->filterkey))
return 1;
break;
default:
if (a->fields[i].val != b->fields[i].val)
return 1;
Expand Down Expand Up @@ -730,6 +750,7 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
u32 fcount = old->field_count;
struct audit_entry *entry;
struct audit_krule *new;
char *fk;
int i, err = 0;

entry = audit_init_entry(fcount);
Expand Down Expand Up @@ -760,6 +781,13 @@ static struct audit_entry *audit_dupe_rule(struct audit_krule *old,
case AUDIT_SE_CLR:
err = audit_dupe_selinux_field(&new->fields[i],
&old->fields[i]);
break;
case AUDIT_FILTERKEY:
fk = kstrdup(old->filterkey, GFP_KERNEL);
if (unlikely(!fk))
err = -ENOMEM;
else
new->filterkey = fk;
}
if (err) {
audit_free_rule(entry);
Expand Down Expand Up @@ -1245,6 +1273,34 @@ static void audit_list_rules(int pid, int seq, struct sk_buff_head *q)
skb_queue_tail(q, skb);
}

/* Log rule additions and removals */
static void audit_log_rule_change(uid_t loginuid, u32 sid, char *action,
struct audit_krule *rule, int res)
{
struct audit_buffer *ab;

ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE);
if (!ab)
return;
audit_log_format(ab, "auid=%u", loginuid);
if (sid) {
char *ctx = NULL;
u32 len;
if (selinux_ctxid_to_string(sid, &ctx, &len))
audit_log_format(ab, " ssid=%u", sid);
else
audit_log_format(ab, " subj=%s", ctx);
kfree(ctx);
}
audit_log_format(ab, " %s rule key=", action);
if (rule->filterkey)
audit_log_untrustedstring(ab, rule->filterkey);
else
audit_log_format(ab, "(null)");
audit_log_format(ab, " list=%d res=%d", rule->listnr, res);
audit_log_end(ab);
}

/**
* audit_receive_filter - apply all rules to the specified message type
* @type: audit message type
Expand Down Expand Up @@ -1304,24 +1360,7 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,

err = audit_add_rule(entry,
&audit_filter_list[entry->rule.listnr]);

if (sid) {
char *ctx = NULL;
u32 len;
if (selinux_ctxid_to_string(sid, &ctx, &len)) {
/* Maybe call audit_panic? */
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u ssid=%u add rule to list=%d res=%d",
loginuid, sid, entry->rule.listnr, !err);
} else
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u subj=%s add rule to list=%d res=%d",
loginuid, ctx, entry->rule.listnr, !err);
kfree(ctx);
} else
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u add rule to list=%d res=%d",
loginuid, entry->rule.listnr, !err);
audit_log_rule_change(loginuid, sid, "add", &entry->rule, !err);

if (err)
audit_free_rule(entry);
Expand All @@ -1337,24 +1376,8 @@ int audit_receive_filter(int type, int pid, int uid, int seq, void *data,

err = audit_del_rule(entry,
&audit_filter_list[entry->rule.listnr]);

if (sid) {
char *ctx = NULL;
u32 len;
if (selinux_ctxid_to_string(sid, &ctx, &len)) {
/* Maybe call audit_panic? */
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u ssid=%u remove rule from list=%d res=%d",
loginuid, sid, entry->rule.listnr, !err);
} else
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u subj=%s remove rule from list=%d res=%d",
loginuid, ctx, entry->rule.listnr, !err);
kfree(ctx);
} else
audit_log(NULL, GFP_KERNEL, AUDIT_CONFIG_CHANGE,
"auid=%u remove rule from list=%d res=%d",
loginuid, entry->rule.listnr, !err);
audit_log_rule_change(loginuid, sid, "remove", &entry->rule,
!err);

audit_free_rule(entry);
break;
Expand Down
15 changes: 15 additions & 0 deletions kernel/auditsc.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -186,6 +186,7 @@ struct audit_context {
int auditable; /* 1 if record should be written */
int name_count;
struct audit_names names[AUDIT_NAMES];
char * filterkey; /* key for rule that triggered record */
struct dentry * pwd;
struct vfsmount * pwdmnt;
struct audit_context *previous; /* For nested syscalls */
Expand Down Expand Up @@ -348,11 +349,17 @@ static int audit_filter_rules(struct task_struct *tsk,
if (ctx)
result = audit_comparator(ctx->argv[f->type-AUDIT_ARG0], f->op, f->val);
break;
case AUDIT_FILTERKEY:
/* ignore this field for filtering */
result = 1;
break;
}

if (!result)
return 0;
}
if (rule->filterkey)
ctx->filterkey = kstrdup(rule->filterkey, GFP_ATOMIC);
switch (rule->action) {
case AUDIT_NEVER: *state = AUDIT_DISABLED; break;
case AUDIT_ALWAYS: *state = AUDIT_RECORD_CONTEXT; break;
Expand Down Expand Up @@ -627,6 +634,7 @@ static inline void audit_free_context(struct audit_context *context)
}
audit_free_names(context);
audit_free_aux(context);
kfree(context->filterkey);
kfree(context);
context = previous;
} while (context);
Expand Down Expand Up @@ -735,6 +743,11 @@ static void audit_log_exit(struct audit_context *context, struct task_struct *ts
context->euid, context->suid, context->fsuid,
context->egid, context->sgid, context->fsgid, tty);
audit_log_task_info(ab, tsk);
if (context->filterkey) {
audit_log_format(ab, " key=");
audit_log_untrustedstring(ab, context->filterkey);
} else
audit_log_format(ab, " key=(null)");
audit_log_end(ab);

for (aux = context->aux; aux; aux = aux->next) {
Expand Down Expand Up @@ -1060,6 +1073,8 @@ void audit_syscall_exit(int valid, long return_code)
} else {
audit_free_names(context);
audit_free_aux(context);
kfree(context->filterkey);
context->filterkey = NULL;
tsk->audit_context = context;
}
}
Expand Down

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