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apparmor: Add support for attaching profiles via xattr, presence and value

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Make it possible to tie Apparmor profiles to the presence of one or more
extended attributes, and optionally their values. An example usecase for
this is to automatically transition to a more privileged Apparmor profile
if an executable has a valid IMA signature, which can then be appraised
by the IMA subsystem.

Signed-off-by: Matthew Garrett <mjg59@google.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>
This commit is contained in:
Matthew Garrett 2018-02-08 12:37:19 -08:00 committed by John Johansen
parent a0781209cb
commit 8e51f9087f
4 changed files with 216 additions and 33 deletions
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150
security/apparmor/domain.c
View File

@ -19,6 +19,7 @@
#include <linux/syscalls.h>
#include <linux/tracehook.h>
#include <linux/personality.h>
#include <linux/xattr.h>
#include "include/audit.h"
#include "include/apparmorfs.h"
@ -301,8 +302,57 @@ static int change_profile_perms(struct aa_profile *profile,
return label_match(profile, target, stack, start, true, request, perms);
}
/**
* aa_xattrs_match - check whether a file matches the xattrs defined in profile
* @bprm: binprm struct for the process to validate
* @profile: profile to match against (NOT NULL)
*
* Returns: number of extended attributes that matched, or < 0 on error
*/
static int aa_xattrs_match(const struct linux_binprm *bprm,
struct aa_profile *profile)
{
int i;
size_t size;
struct dentry *d;
char *value = NULL;
int value_size = 0, ret = profile->xattr_count;
if (!bprm || !profile->xattr_count)
return 0;
d = bprm->file->f_path.dentry;
for (i = 0; i < profile->xattr_count; i++) {
size = vfs_getxattr_alloc(d, profile->xattrs[i], &value,
value_size, GFP_KERNEL);
if (size < 0) {
ret = -EINVAL;
goto out;
}
/* Check the xattr value, not just presence */
if (profile->xattr_lens[i]) {
if (profile->xattr_lens[i] != size) {
ret = -EINVAL;
goto out;
}
if (memcmp(value, profile->xattr_values[i], size)) {
ret = -EINVAL;
goto out;
}
}
}
out:
kfree(value);
return ret;
}
/**
* __attach_match_ - find an attachment match
* @bprm - binprm structure of transitioning task
* @name - to match against (NOT NULL)
* @head - profile list to walk (NOT NULL)
* @info - info message if there was an error (NOT NULL)
@ -316,11 +366,12 @@ static int change_profile_perms(struct aa_profile *profile,
*
* Returns: profile or NULL if no match found
*/
static struct aa_profile *__attach_match(const char *name,
static struct aa_profile *__attach_match(const struct linux_binprm *bprm,
const char *name,
struct list_head *head,
const char **info)
{
int len = 0;
int len = 0, xattrs = 0;
bool conflict = false;
struct aa_profile *profile, *candidate = NULL;
@ -329,26 +380,56 @@ static struct aa_profile *__attach_match(const char *name,
&profile->label == ns_unconfined(profile->ns))
continue;
/* Find the "best" matching profile. Profiles must
* match the path and extended attributes (if any)
* associated with the file. A more specific path
* match will be preferred over a less specific one,
* and a match with more matching extended attributes
* will be preferred over one with fewer. If the best
* match has both the same level of path specificity
* and the same number of matching extended attributes
* as another profile, signal a conflict and refuse to
* match.
*/
if (profile->xmatch) {
if (profile->xmatch_len >= len) {
unsigned int state;
u32 perm;
unsigned int state;
u32 perm;
state = aa_dfa_match(profile->xmatch,
DFA_START, name);
perm = dfa_user_allow(profile->xmatch, state);
/* any accepting state means a valid match. */
if (perm & MAY_EXEC) {
if (profile->xmatch_len == len) {
if (profile->xmatch_len < len)
continue;
state = aa_dfa_match(profile->xmatch,
DFA_START, name);
perm = dfa_user_allow(profile->xmatch, state);
/* any accepting state means a valid match. */
if (perm & MAY_EXEC) {
int ret = aa_xattrs_match(bprm, profile);
/* Fail matching if the xattrs don't match */
if (ret < 0)
continue;
/* The new match isn't more specific
* than the current best match
*/
if (profile->xmatch_len == len &&
ret <= xattrs) {
/* Match is equivalent, so conflict */
if (ret == xattrs)
conflict = true;
continue;
}
candidate = profile;
len = profile->xmatch_len;
conflict = false;
continue;
}
/* Either the same length with more matching
* xattrs, or a longer match
*/
candidate = profile;
len = profile->xmatch_len;
xattrs = ret;
conflict = false;
}
} else if (!strcmp(profile->base.name, name))
} else if (!strcmp(profile->base.name, name) &&
aa_xattrs_match(bprm, profile) >= 0)
/* exact non-re match, no more searching required */
return profile;
}
@ -363,6 +444,7 @@ static struct aa_profile *__attach_match(const char *name,
/**
* find_attach - do attachment search for unconfined processes
* @bprm - binprm structure of transitioning task
* @ns: the current namespace (NOT NULL)
* @list: list to search (NOT NULL)
* @name: the executable name to match against (NOT NULL)
@ -370,13 +452,14 @@ static struct aa_profile *__attach_match(const char *name,
*
* Returns: label or NULL if no match found
*/
static struct aa_label *find_attach(struct aa_ns *ns, struct list_head *list,
static struct aa_label *find_attach(const struct linux_binprm *bprm,
struct aa_ns *ns, struct list_head *list,
const char *name, const char **info)
{
struct aa_profile *profile;
rcu_read_lock();
profile = aa_get_profile(__attach_match(name, list, info));
profile = aa_get_profile(__attach_match(bprm, name, list, info));
rcu_read_unlock();
return profile ? &profile->label : NULL;
@ -432,6 +515,7 @@ struct aa_label *x_table_lookup(struct aa_profile *profile, u32 xindex,
/**
* x_to_label - get target label for a given xindex
* @profile: current profile (NOT NULL)
* @bprm: binprm structure of transitioning task
* @name: name to lookup (NOT NULL)
* @xindex: index into x transition table
* @lookupname: returns: name used in lookup if one was specified (NOT NULL)
@ -441,6 +525,7 @@ struct aa_label *x_table_lookup(struct aa_profile *profile, u32 xindex,
* Returns: refcounted label or NULL if not found available
*/
static struct aa_label *x_to_label(struct aa_profile *profile,
const struct linux_binprm *bprm,
const char *name, u32 xindex,
const char **lookupname,
const char **info)
@ -468,11 +553,11 @@ static struct aa_label *x_to_label(struct aa_profile *profile,
case AA_X_NAME:
if (xindex & AA_X_CHILD)
/* released by caller */
new = find_attach(ns, &profile->base.profiles,
new = find_attach(bprm, ns, &profile->base.profiles,
name, info);
else
/* released by caller */
new = find_attach(ns, &ns->base.profiles,
new = find_attach(bprm, ns, &ns->base.profiles,
name, info);
*lookupname = name;
break;
@ -512,6 +597,8 @@ static struct aa_label *profile_transition(struct aa_profile *profile,
bool *secure_exec)
{
struct aa_label *new = NULL;
struct aa_profile *component;
struct label_it i;
const char *info = NULL, *name = NULL, *target = NULL;
unsigned int state = profile->file.start;
struct aa_perms perms = {};
@ -536,8 +623,8 @@ static struct aa_label *profile_transition(struct aa_profile *profile,
}
if (profile_unconfined(profile)) {
new = find_attach(profile->ns, &profile->ns->base.profiles,
name, &info);
new = find_attach(bprm, profile->ns,
&profile->ns->base.profiles, name, &info);
if (new) {
AA_DEBUG("unconfined attached to new label");
return new;
@ -550,7 +637,8 @@ static struct aa_label *profile_transition(struct aa_profile *profile,
state = aa_str_perms(profile->file.dfa, state, name, cond, &perms);
if (perms.allow & MAY_EXEC) {
/* exec permission determine how to transition */
new = x_to_label(profile, name, perms.xindex, &target, &info);
new = x_to_label(profile, bprm, name, perms.xindex, &target,
&info);
if (new && new->proxy == profile->label.proxy && info) {
/* hack ix fallback - improve how this is detected */
goto audit;
@ -559,6 +647,20 @@ static struct aa_label *profile_transition(struct aa_profile *profile,
info = "profile transition not found";
/* remove MAY_EXEC to audit as failure */
perms.allow &= ~MAY_EXEC;
} else {
/* verify that each component's xattr requirements are
* met, and fail execution otherwise
*/
label_for_each(i, new, component) {
if (aa_xattrs_match(bprm, component) < 0) {
error = -EACCES;
info = "required xattrs not present";
perms.allow &= ~MAY_EXEC;
aa_put_label(new);
new = NULL;
goto audit;
}
}
}
} else if (COMPLAIN_MODE(profile)) {
/* no exec permission - learning mode */

6
security/apparmor/include/policy.h
View File

@ -148,6 +148,12 @@ struct aa_profile {
struct aa_policydb policy;
struct aa_file_rules file;
struct aa_caps caps;
int xattr_count;
char **xattrs;
size_t *xattr_lens;
char **xattr_values;
struct aa_rlimit rlimits;
struct aa_loaddata *rawdata;

8
security/apparmor/policy.c
View File

@ -210,6 +210,7 @@ static void aa_free_data(void *ptr, void *arg)
void aa_free_profile(struct aa_profile *profile)
{
struct rhashtable *rht;
int i;
AA_DEBUG("%s(%p)\n", __func__, profile);
@ -227,6 +228,13 @@ void aa_free_profile(struct aa_profile *profile)
aa_free_cap_rules(&profile->caps);
aa_free_rlimit_rules(&profile->rlimits);
for (i = 0; i < profile->xattr_count; i++) {
kzfree(profile->xattrs[i]);
kzfree(profile->xattr_values[i]);
}
kzfree(profile->xattrs);
kzfree(profile->xattr_lens);
kzfree(profile->xattr_values);
kzfree(profile->dirname);
aa_put_dfa(profile->xmatch);
aa_put_dfa(profile->policy.dfa);

85
security/apparmor/policy_unpack.c
View File

@ -203,6 +203,15 @@ static bool inbounds(struct aa_ext *e, size_t size)
return (size <= e->end - e->pos);
}
static void *kvmemdup(const void *src, size_t len)
{
void *p = kvmalloc(len, GFP_KERNEL);
if (p)
memcpy(p, src, len);
return p;
}
/**
* aa_u16_chunck - test and do bounds checking for a u16 size based chunk
* @e: serialized data read head (NOT NULL)
@ -522,6 +531,68 @@ fail:
return 0;
}
static bool unpack_xattrs(struct aa_ext *e, struct aa_profile *profile)
{
void *pos = e->pos;
if (unpack_nameX(e, AA_STRUCT, "xattrs")) {
int i, size;
size = unpack_array(e, NULL);
profile->xattr_count = size;
profile->xattrs = kcalloc(size, sizeof(char *),
GFP_KERNEL);
if (!profile->xattrs)
goto fail;
for (i = 0; i < size; i++) {
if (!unpack_strdup(e, &profile->xattrs[i], NULL))
goto fail;
}
if (!unpack_nameX(e, AA_ARRAYEND, NULL))
goto fail;
if (!unpack_nameX(e, AA_STRUCTEND, NULL))
goto fail;
}
if (unpack_nameX(e, AA_STRUCT, "xattr_values")) {
int i, size;
size = unpack_array(e, NULL);
/* Must be the same number of xattr values as xattrs */
if (size != profile->xattr_count)
goto fail;
profile->xattr_lens = kcalloc(size, sizeof(size_t),
GFP_KERNEL);
if (!profile->xattr_lens)
goto fail;
profile->xattr_values = kcalloc(size, sizeof(char *),
GFP_KERNEL);
if (!profile->xattr_values)
goto fail;
for (i = 0; i < size; i++) {
profile->xattr_lens[i] = unpack_blob(e,
&profile->xattr_values[i], NULL);
profile->xattr_values[i] =
kvmemdup(profile->xattr_values[i],
profile->xattr_lens[i]);
}
if (!unpack_nameX(e, AA_ARRAYEND, NULL))
goto fail;
if (!unpack_nameX(e, AA_STRUCTEND, NULL))
goto fail;
}
return 1;
fail:
e->pos = pos;
return 0;
}
static bool unpack_rlimits(struct aa_ext *e, struct aa_profile *profile)
{
void *pos = e->pos;
@ -556,15 +627,6 @@ fail:
return 0;
}
static void *kvmemdup(const void *src, size_t len)
{
void *p = kvmalloc(len, GFP_KERNEL);
if (p)
memcpy(p, src, len);
return p;
}
static u32 strhash(const void *data, u32 len, u32 seed)
{
const char * const *key = data;
@ -719,6 +781,11 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
goto fail;
}
if (!unpack_xattrs(e, profile)) {
info = "failed to unpack profile xattrs";
goto fail;
}
if (!unpack_rlimits(e, profile)) {
info = "failed to unpack profile rlimits";
goto fail;