alistair23-linux/security/smack/smack_access.c
Andrey Ryabinin 5c1b66240b security: smack: fix out-of-bounds access in smk_parse_smack()
Setting smack label on file (e.g. 'attr -S -s SMACK64 -V "test" test')
triggered following spew on the kernel with KASan applied:
    ==================================================================
    BUG: AddressSanitizer: out of bounds access in strncpy+0x28/0x60 at addr ffff8800059ad064
    =============================================================================
    BUG kmalloc-8 (Not tainted): kasan error
    -----------------------------------------------------------------------------

    Disabling lock debugging due to kernel taint
    INFO: Slab 0xffffea0000166b40 objects=128 used=7 fp=0xffff8800059ad080 flags=0x4000000000000080
    INFO: Object 0xffff8800059ad060 @offset=96 fp=0xffff8800059ad080

    Bytes b4 ffff8800059ad050: a0 df 9a 05 00 88 ff ff 5a 5a 5a 5a 5a 5a 5a 5a  ........ZZZZZZZZ
    Object ffff8800059ad060: 74 65 73 74 6b 6b 6b a5                          testkkk.
    Redzone ffff8800059ad068: cc cc cc cc cc cc cc cc                          ........
    Padding ffff8800059ad078: 5a 5a 5a 5a 5a 5a 5a 5a                          ZZZZZZZZ
    CPU: 0 PID: 528 Comm: attr Tainted: G    B          3.18.0-rc1-mm1+ #5
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
     0000000000000000 ffff8800059ad064 ffffffff81534cf2 ffff880005a5bc40
     ffffffff8112fe1a 0000000100800006 0000000f059ad060 ffff880006000f90
     0000000000000296 ffffea0000166b40 ffffffff8107ca97 ffff880005891060
    Call Trace:
    ? dump_stack (lib/dump_stack.c:52)
    ? kasan_report_error (mm/kasan/report.c:102 mm/kasan/report.c:178)
    ? preempt_count_sub (kernel/sched/core.c:2651)
    ? __asan_load1 (mm/kasan/kasan.h:50 mm/kasan/kasan.c:248 mm/kasan/kasan.c:358)
    ? strncpy (lib/string.c:121)
    ? strncpy (lib/string.c:121)
    ? smk_parse_smack (security/smack/smack_access.c:457)
    ? setxattr (fs/xattr.c:343)
    ? smk_import_entry (security/smack/smack_access.c:514)
    ? smack_inode_setxattr (security/smack/smack_lsm.c:1093 (discriminator 1))
    ? security_inode_setxattr (security/security.c:602)
    ? vfs_setxattr (fs/xattr.c:134)
    ? setxattr (fs/xattr.c:343)
    ? setxattr (fs/xattr.c:360)
    ? get_parent_ip (kernel/sched/core.c:2606)
    ? preempt_count_sub (kernel/sched/core.c:2651)
    ? __percpu_counter_add (arch/x86/include/asm/preempt.h:98 lib/percpu_counter.c:90)
    ? get_parent_ip (kernel/sched/core.c:2606)
    ? preempt_count_sub (kernel/sched/core.c:2651)
    ? __mnt_want_write (arch/x86/include/asm/preempt.h:98 fs/namespace.c:359)
    ? path_setxattr (fs/xattr.c:380)
    ? SyS_lsetxattr (fs/xattr.c:397)
    ? system_call_fastpath (arch/x86/kernel/entry_64.S:423)
    Read of size 1 by task attr:
    Memory state around the buggy address:
     ffff8800059ace80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     ffff8800059acf00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
     ffff8800059acf80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
    >ffff8800059ad000: 00 fc fc fc 00 fc fc fc 05 fc fc fc 04 fc fc fc
                                                           ^
     ffff8800059ad080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
     ffff8800059ad100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
     ffff8800059ad180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
    ==================================================================

strncpy() copies one byte more than the source string has.
Fix this by passing the correct length to strncpy().

Now we can remove initialization of the last byte in 'smack' string
because kzalloc() already did this for us.

Signed-off-by: Andrey Ryabinin <a.ryabinin@samsung.com>
2014-11-21 13:14:22 -08:00

592 lines
14 KiB
C

/*
* Copyright (C) 2007 Casey Schaufler <casey@schaufler-ca.com>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, version 2.
*
* Author:
* Casey Schaufler <casey@schaufler-ca.com>
*
*/
#include <linux/types.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/sched.h>
#include "smack.h"
struct smack_known smack_known_huh = {
.smk_known = "?",
.smk_secid = 2,
};
struct smack_known smack_known_hat = {
.smk_known = "^",
.smk_secid = 3,
};
struct smack_known smack_known_star = {
.smk_known = "*",
.smk_secid = 4,
};
struct smack_known smack_known_floor = {
.smk_known = "_",
.smk_secid = 5,
};
struct smack_known smack_known_invalid = {
.smk_known = "",
.smk_secid = 6,
};
struct smack_known smack_known_web = {
.smk_known = "@",
.smk_secid = 7,
};
LIST_HEAD(smack_known_list);
/*
* The initial value needs to be bigger than any of the
* known values above.
*/
static u32 smack_next_secid = 10;
/*
* what events do we log
* can be overwritten at run-time by /smack/logging
*/
int log_policy = SMACK_AUDIT_DENIED;
/**
* smk_access_entry - look up matching access rule
* @subject_label: a pointer to the subject's Smack label
* @object_label: a pointer to the object's Smack label
* @rule_list: the list of rules to search
*
* This function looks up the subject/object pair in the
* access rule list and returns the access mode. If no
* entry is found returns -ENOENT.
*
* NOTE:
*
* Earlier versions of this function allowed for labels that
* were not on the label list. This was done to allow for
* labels to come over the network that had never been seen
* before on this host. Unless the receiving socket has the
* star label this will always result in a failure check. The
* star labeled socket case is now handled in the networking
* hooks so there is no case where the label is not on the
* label list. Checking to see if the address of two labels
* is the same is now a reliable test.
*
* Do the object check first because that is more
* likely to differ.
*
* Allowing write access implies allowing locking.
*/
int smk_access_entry(char *subject_label, char *object_label,
struct list_head *rule_list)
{
int may = -ENOENT;
struct smack_rule *srp;
list_for_each_entry_rcu(srp, rule_list, list) {
if (srp->smk_object->smk_known == object_label &&
srp->smk_subject->smk_known == subject_label) {
may = srp->smk_access;
break;
}
}
/*
* MAY_WRITE implies MAY_LOCK.
*/
if ((may & MAY_WRITE) == MAY_WRITE)
may |= MAY_LOCK;
return may;
}
/**
* smk_access - determine if a subject has a specific access to an object
* @subject: a pointer to the subject's Smack label entry
* @object: a pointer to the object's Smack label entry
* @request: the access requested, in "MAY" format
* @a : a pointer to the audit data
*
* This function looks up the subject/object pair in the
* access rule list and returns 0 if the access is permitted,
* non zero otherwise.
*
* Smack labels are shared on smack_list
*/
int smk_access(struct smack_known *subject, struct smack_known *object,
int request, struct smk_audit_info *a)
{
int may = MAY_NOT;
int rc = 0;
/*
* Hardcoded comparisons.
*
* A star subject can't access any object.
*/
if (subject == &smack_known_star) {
rc = -EACCES;
goto out_audit;
}
/*
* An internet object can be accessed by any subject.
* Tasks cannot be assigned the internet label.
* An internet subject can access any object.
*/
if (object == &smack_known_web || subject == &smack_known_web)
goto out_audit;
/*
* A star object can be accessed by any subject.
*/
if (object == &smack_known_star)
goto out_audit;
/*
* An object can be accessed in any way by a subject
* with the same label.
*/
if (subject->smk_known == object->smk_known)
goto out_audit;
/*
* A hat subject can read or lock any object.
* A floor object can be read or locked by any subject.
*/
if ((request & MAY_ANYREAD) == request ||
(request & MAY_LOCK) == request) {
if (object == &smack_known_floor)
goto out_audit;
if (subject == &smack_known_hat)
goto out_audit;
}
/*
* Beyond here an explicit relationship is required.
* If the requested access is contained in the available
* access (e.g. read is included in readwrite) it's
* good. A negative response from smk_access_entry()
* indicates there is no entry for this pair.
*/
rcu_read_lock();
may = smk_access_entry(subject->smk_known, object->smk_known,
&subject->smk_rules);
rcu_read_unlock();
if (may <= 0 || (request & may) != request) {
rc = -EACCES;
goto out_audit;
}
#ifdef CONFIG_SECURITY_SMACK_BRINGUP
/*
* Return a positive value if using bringup mode.
* This allows the hooks to identify checks that
* succeed because of "b" rules.
*/
if (may & MAY_BRINGUP)
rc = MAY_BRINGUP;
#endif
out_audit:
#ifdef CONFIG_AUDIT
if (a)
smack_log(subject->smk_known, object->smk_known,
request, rc, a);
#endif
return rc;
}
/**
* smk_tskacc - determine if a task has a specific access to an object
* @tsp: a pointer to the subject's task
* @obj_known: a pointer to the object's label entry
* @mode: the access requested, in "MAY" format
* @a : common audit data
*
* This function checks the subject task's label/object label pair
* in the access rule list and returns 0 if the access is permitted,
* non zero otherwise. It allows that the task may have the capability
* to override the rules.
*/
int smk_tskacc(struct task_smack *tsp, struct smack_known *obj_known,
u32 mode, struct smk_audit_info *a)
{
struct smack_known *sbj_known = smk_of_task(tsp);
int may;
int rc;
/*
* Check the global rule list
*/
rc = smk_access(sbj_known, obj_known, mode, NULL);
if (rc >= 0) {
/*
* If there is an entry in the task's rule list
* it can further restrict access.
*/
may = smk_access_entry(sbj_known->smk_known,
obj_known->smk_known,
&tsp->smk_rules);
if (may < 0)
goto out_audit;
if ((mode & may) == mode)
goto out_audit;
rc = -EACCES;
}
/*
* Allow for priviliged to override policy.
*/
if (rc != 0 && smack_privileged(CAP_MAC_OVERRIDE))
rc = 0;
out_audit:
#ifdef CONFIG_AUDIT
if (a)
smack_log(sbj_known->smk_known, obj_known->smk_known,
mode, rc, a);
#endif
return rc;
}
/**
* smk_curacc - determine if current has a specific access to an object
* @obj_known: a pointer to the object's Smack label entry
* @mode: the access requested, in "MAY" format
* @a : common audit data
*
* This function checks the current subject label/object label pair
* in the access rule list and returns 0 if the access is permitted,
* non zero otherwise. It allows that current may have the capability
* to override the rules.
*/
int smk_curacc(struct smack_known *obj_known,
u32 mode, struct smk_audit_info *a)
{
struct task_smack *tsp = current_security();
return smk_tskacc(tsp, obj_known, mode, a);
}
#ifdef CONFIG_AUDIT
/**
* smack_str_from_perm : helper to transalate an int to a
* readable string
* @string : the string to fill
* @access : the int
*
*/
static inline void smack_str_from_perm(char *string, int access)
{
int i = 0;
if (access & MAY_READ)
string[i++] = 'r';
if (access & MAY_WRITE)
string[i++] = 'w';
if (access & MAY_EXEC)
string[i++] = 'x';
if (access & MAY_APPEND)
string[i++] = 'a';
if (access & MAY_TRANSMUTE)
string[i++] = 't';
if (access & MAY_LOCK)
string[i++] = 'l';
string[i] = '\0';
}
/**
* smack_log_callback - SMACK specific information
* will be called by generic audit code
* @ab : the audit_buffer
* @a : audit_data
*
*/
static void smack_log_callback(struct audit_buffer *ab, void *a)
{
struct common_audit_data *ad = a;
struct smack_audit_data *sad = ad->smack_audit_data;
audit_log_format(ab, "lsm=SMACK fn=%s action=%s",
ad->smack_audit_data->function,
sad->result ? "denied" : "granted");
audit_log_format(ab, " subject=");
audit_log_untrustedstring(ab, sad->subject);
audit_log_format(ab, " object=");
audit_log_untrustedstring(ab, sad->object);
if (sad->request[0] == '\0')
audit_log_format(ab, " labels_differ");
else
audit_log_format(ab, " requested=%s", sad->request);
}
/**
* smack_log - Audit the granting or denial of permissions.
* @subject_label : smack label of the requester
* @object_label : smack label of the object being accessed
* @request: requested permissions
* @result: result from smk_access
* @a: auxiliary audit data
*
* Audit the granting or denial of permissions in accordance
* with the policy.
*/
void smack_log(char *subject_label, char *object_label, int request,
int result, struct smk_audit_info *ad)
{
char request_buffer[SMK_NUM_ACCESS_TYPE + 1];
struct smack_audit_data *sad;
struct common_audit_data *a = &ad->a;
#ifdef CONFIG_SECURITY_SMACK_BRINGUP
/*
* The result may be positive in bringup mode.
*/
if (result > 0)
result = 0;
#endif
/* check if we have to log the current event */
if (result != 0 && (log_policy & SMACK_AUDIT_DENIED) == 0)
return;
if (result == 0 && (log_policy & SMACK_AUDIT_ACCEPT) == 0)
return;
sad = a->smack_audit_data;
if (sad->function == NULL)
sad->function = "unknown";
/* end preparing the audit data */
smack_str_from_perm(request_buffer, request);
sad->subject = subject_label;
sad->object = object_label;
sad->request = request_buffer;
sad->result = result;
common_lsm_audit(a, smack_log_callback, NULL);
}
#else /* #ifdef CONFIG_AUDIT */
void smack_log(char *subject_label, char *object_label, int request,
int result, struct smk_audit_info *ad)
{
}
#endif
DEFINE_MUTEX(smack_known_lock);
struct hlist_head smack_known_hash[SMACK_HASH_SLOTS];
/**
* smk_insert_entry - insert a smack label into a hash map,
*
* this function must be called under smack_known_lock
*/
void smk_insert_entry(struct smack_known *skp)
{
unsigned int hash;
struct hlist_head *head;
hash = full_name_hash(skp->smk_known, strlen(skp->smk_known));
head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
hlist_add_head_rcu(&skp->smk_hashed, head);
list_add_rcu(&skp->list, &smack_known_list);
}
/**
* smk_find_entry - find a label on the list, return the list entry
* @string: a text string that might be a Smack label
*
* Returns a pointer to the entry in the label list that
* matches the passed string.
*/
struct smack_known *smk_find_entry(const char *string)
{
unsigned int hash;
struct hlist_head *head;
struct smack_known *skp;
hash = full_name_hash(string, strlen(string));
head = &smack_known_hash[hash & (SMACK_HASH_SLOTS - 1)];
hlist_for_each_entry_rcu(skp, head, smk_hashed)
if (strcmp(skp->smk_known, string) == 0)
return skp;
return NULL;
}
/**
* smk_parse_smack - parse smack label from a text string
* @string: a text string that might contain a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
*
* Returns a pointer to the clean label, or NULL
*/
char *smk_parse_smack(const char *string, int len)
{
char *smack;
int i;
if (len <= 0)
len = strlen(string) + 1;
/*
* Reserve a leading '-' as an indicator that
* this isn't a label, but an option to interfaces
* including /smack/cipso and /smack/cipso2
*/
if (string[0] == '-')
return NULL;
for (i = 0; i < len; i++)
if (string[i] > '~' || string[i] <= ' ' || string[i] == '/' ||
string[i] == '"' || string[i] == '\\' || string[i] == '\'')
break;
if (i == 0 || i >= SMK_LONGLABEL)
return NULL;
smack = kzalloc(i + 1, GFP_KERNEL);
if (smack != NULL)
strncpy(smack, string, i);
return smack;
}
/**
* smk_netlbl_mls - convert a catset to netlabel mls categories
* @catset: the Smack categories
* @sap: where to put the netlabel categories
*
* Allocates and fills attr.mls
* Returns 0 on success, error code on failure.
*/
int smk_netlbl_mls(int level, char *catset, struct netlbl_lsm_secattr *sap,
int len)
{
unsigned char *cp;
unsigned char m;
int cat;
int rc;
int byte;
sap->flags |= NETLBL_SECATTR_MLS_CAT;
sap->attr.mls.lvl = level;
sap->attr.mls.cat = NULL;
for (cat = 1, cp = catset, byte = 0; byte < len; cp++, byte++)
for (m = 0x80; m != 0; m >>= 1, cat++) {
if ((m & *cp) == 0)
continue;
rc = netlbl_catmap_setbit(&sap->attr.mls.cat,
cat, GFP_ATOMIC);
if (rc < 0) {
netlbl_catmap_free(sap->attr.mls.cat);
return rc;
}
}
return 0;
}
/**
* smk_import_entry - import a label, return the list entry
* @string: a text string that might be a Smack label
* @len: the maximum size, or zero if it is NULL terminated.
*
* Returns a pointer to the entry in the label list that
* matches the passed string, adding it if necessary.
*/
struct smack_known *smk_import_entry(const char *string, int len)
{
struct smack_known *skp;
char *smack;
int slen;
int rc;
smack = smk_parse_smack(string, len);
if (smack == NULL)
return NULL;
mutex_lock(&smack_known_lock);
skp = smk_find_entry(smack);
if (skp != NULL)
goto freeout;
skp = kzalloc(sizeof(*skp), GFP_KERNEL);
if (skp == NULL)
goto freeout;
skp->smk_known = smack;
skp->smk_secid = smack_next_secid++;
skp->smk_netlabel.domain = skp->smk_known;
skp->smk_netlabel.flags =
NETLBL_SECATTR_DOMAIN | NETLBL_SECATTR_MLS_LVL;
/*
* If direct labeling works use it.
* Otherwise use mapped labeling.
*/
slen = strlen(smack);
if (slen < SMK_CIPSOLEN)
rc = smk_netlbl_mls(smack_cipso_direct, skp->smk_known,
&skp->smk_netlabel, slen);
else
rc = smk_netlbl_mls(smack_cipso_mapped, (char *)&skp->smk_secid,
&skp->smk_netlabel, sizeof(skp->smk_secid));
if (rc >= 0) {
INIT_LIST_HEAD(&skp->smk_rules);
mutex_init(&skp->smk_rules_lock);
/*
* Make sure that the entry is actually
* filled before putting it on the list.
*/
smk_insert_entry(skp);
goto unlockout;
}
/*
* smk_netlbl_mls failed.
*/
kfree(skp);
skp = NULL;
freeout:
kfree(smack);
unlockout:
mutex_unlock(&smack_known_lock);
return skp;
}
/**
* smack_from_secid - find the Smack label associated with a secid
* @secid: an integer that might be associated with a Smack label
*
* Returns a pointer to the appropriate Smack label entry if there is one,
* otherwise a pointer to the invalid Smack label.
*/
struct smack_known *smack_from_secid(const u32 secid)
{
struct smack_known *skp;
rcu_read_lock();
list_for_each_entry_rcu(skp, &smack_known_list, list) {
if (skp->smk_secid == secid) {
rcu_read_unlock();
return skp;
}
}
/*
* If we got this far someone asked for the translation
* of a secid that is not on the list.
*/
rcu_read_unlock();
return &smack_known_invalid;
}