summaryrefslogtreecommitdiffstats
path: root/security/device_cgroup.c
diff options
context:
space:
mode:
Diffstat (limited to 'security/device_cgroup.c')
-rw-r--r--security/device_cgroup.c449
1 files changed, 283 insertions, 166 deletions
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 442204cc22d..19ecc8de9e6 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -26,12 +26,12 @@
static DEFINE_MUTEX(devcgroup_mutex);
/*
- * whitelist locking rules:
+ * exception list locking rules:
* hold devcgroup_mutex for update/read.
* hold rcu_read_lock() for read.
*/
-struct dev_whitelist_item {
+struct dev_exception_item {
u32 major, minor;
short type;
short access;
@@ -41,7 +41,11 @@ struct dev_whitelist_item {
struct dev_cgroup {
struct cgroup_subsys_state css;
- struct list_head whitelist;
+ struct list_head exceptions;
+ enum {
+ DEVCG_DEFAULT_ALLOW,
+ DEVCG_DEFAULT_DENY,
+ } behavior;
};
static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -74,12 +78,14 @@ static int devcgroup_can_attach(struct cgroup *new_cgrp,
/*
* called under devcgroup_mutex
*/
-static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
+static int dev_exceptions_copy(struct list_head *dest, struct list_head *orig)
{
- struct dev_whitelist_item *wh, *tmp, *new;
+ struct dev_exception_item *ex, *tmp, *new;
- list_for_each_entry(wh, orig, list) {
- new = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
+ lockdep_assert_held(&devcgroup_mutex);
+
+ list_for_each_entry(ex, orig, list) {
+ new = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
if (!new)
goto free_and_exit;
list_add_tail(&new->list, dest);
@@ -88,64 +94,64 @@ static int dev_whitelist_copy(struct list_head *dest, struct list_head *orig)
return 0;
free_and_exit:
- list_for_each_entry_safe(wh, tmp, dest, list) {
- list_del(&wh->list);
- kfree(wh);
+ list_for_each_entry_safe(ex, tmp, dest, list) {
+ list_del(&ex->list);
+ kfree(ex);
}
return -ENOMEM;
}
-/* Stupid prototype - don't bother combining existing entries */
/*
* called under devcgroup_mutex
*/
-static int dev_whitelist_add(struct dev_cgroup *dev_cgroup,
- struct dev_whitelist_item *wh)
+static int dev_exception_add(struct dev_cgroup *dev_cgroup,
+ struct dev_exception_item *ex)
{
- struct dev_whitelist_item *whcopy, *walk;
+ struct dev_exception_item *excopy, *walk;
+
+ lockdep_assert_held(&devcgroup_mutex);
- whcopy = kmemdup(wh, sizeof(*wh), GFP_KERNEL);
- if (!whcopy)
+ excopy = kmemdup(ex, sizeof(*ex), GFP_KERNEL);
+ if (!excopy)
return -ENOMEM;
- list_for_each_entry(walk, &dev_cgroup->whitelist, list) {
- if (walk->type != wh->type)
+ list_for_each_entry(walk, &dev_cgroup->exceptions, list) {
+ if (walk->type != ex->type)
continue;
- if (walk->major != wh->major)
+ if (walk->major != ex->major)
continue;
- if (walk->minor != wh->minor)
+ if (walk->minor != ex->minor)
continue;
- walk->access |= wh->access;
- kfree(whcopy);
- whcopy = NULL;
+ walk->access |= ex->access;
+ kfree(excopy);
+ excopy = NULL;
}
- if (whcopy != NULL)
- list_add_tail_rcu(&whcopy->list, &dev_cgroup->whitelist);
+ if (excopy != NULL)
+ list_add_tail_rcu(&excopy->list, &dev_cgroup->exceptions);
return 0;
}
/*
* called under devcgroup_mutex
*/
-static void dev_whitelist_rm(struct dev_cgroup *dev_cgroup,
- struct dev_whitelist_item *wh)
+static void dev_exception_rm(struct dev_cgroup *dev_cgroup,
+ struct dev_exception_item *ex)
{
- struct dev_whitelist_item *walk, *tmp;
+ struct dev_exception_item *walk, *tmp;
+
+ lockdep_assert_held(&devcgroup_mutex);
- list_for_each_entry_safe(walk, tmp, &dev_cgroup->whitelist, list) {
- if (walk->type == DEV_ALL)
- goto remove;
- if (walk->type != wh->type)
+ list_for_each_entry_safe(walk, tmp, &dev_cgroup->exceptions, list) {
+ if (walk->type != ex->type)
continue;
- if (walk->major != ~0 && walk->major != wh->major)
+ if (walk->major != ex->major)
continue;
- if (walk->minor != ~0 && walk->minor != wh->minor)
+ if (walk->minor != ex->minor)
continue;
-remove:
- walk->access &= ~wh->access;
+ walk->access &= ~ex->access;
if (!walk->access) {
list_del_rcu(&walk->list);
kfree_rcu(walk, rcu);
@@ -153,10 +159,28 @@ remove:
}
}
+/**
+ * dev_exception_clean - frees all entries of the exception list
+ * @dev_cgroup: dev_cgroup with the exception list to be cleaned
+ *
+ * called under devcgroup_mutex
+ */
+static void dev_exception_clean(struct dev_cgroup *dev_cgroup)
+{
+ struct dev_exception_item *ex, *tmp;
+
+ lockdep_assert_held(&devcgroup_mutex);
+
+ list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) {
+ list_del_rcu(&ex->list);
+ kfree_rcu(ex, rcu);
+ }
+}
+
/*
* called from kernel/cgroup.c with cgroup_lock() held.
*/
-static struct cgroup_subsys_state *devcgroup_create(struct cgroup *cgroup)
+static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup)
{
struct dev_cgroup *dev_cgroup, *parent_dev_cgroup;
struct cgroup *parent_cgroup;
@@ -165,25 +189,17 @@ static struct cgroup_subsys_state *devcgroup_create(struct cgroup *cgroup)
dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL);
if (!dev_cgroup)
return ERR_PTR(-ENOMEM);
- INIT_LIST_HEAD(&dev_cgroup->whitelist);
+ INIT_LIST_HEAD(&dev_cgroup->exceptions);
parent_cgroup = cgroup->parent;
- if (parent_cgroup == NULL) {
- struct dev_whitelist_item *wh;
- wh = kmalloc(sizeof(*wh), GFP_KERNEL);
- if (!wh) {
- kfree(dev_cgroup);
- return ERR_PTR(-ENOMEM);
- }
- wh->minor = wh->major = ~0;
- wh->type = DEV_ALL;
- wh->access = ACC_MASK;
- list_add(&wh->list, &dev_cgroup->whitelist);
- } else {
+ if (parent_cgroup == NULL)
+ dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW;
+ else {
parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup);
mutex_lock(&devcgroup_mutex);
- ret = dev_whitelist_copy(&dev_cgroup->whitelist,
- &parent_dev_cgroup->whitelist);
+ ret = dev_exceptions_copy(&dev_cgroup->exceptions,
+ &parent_dev_cgroup->exceptions);
+ dev_cgroup->behavior = parent_dev_cgroup->behavior;
mutex_unlock(&devcgroup_mutex);
if (ret) {
kfree(dev_cgroup);
@@ -194,16 +210,12 @@ static struct cgroup_subsys_state *devcgroup_create(struct cgroup *cgroup)
return &dev_cgroup->css;
}
-static void devcgroup_destroy(struct cgroup *cgroup)
+static void devcgroup_css_free(struct cgroup *cgroup)
{
struct dev_cgroup *dev_cgroup;
- struct dev_whitelist_item *wh, *tmp;
dev_cgroup = cgroup_to_devcgroup(cgroup);
- list_for_each_entry_safe(wh, tmp, &dev_cgroup->whitelist, list) {
- list_del(&wh->list);
- kfree(wh);
- }
+ dev_exception_clean(dev_cgroup);
kfree(dev_cgroup);
}
@@ -249,59 +261,91 @@ static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
struct seq_file *m)
{
struct dev_cgroup *devcgroup = cgroup_to_devcgroup(cgroup);
- struct dev_whitelist_item *wh;
+ struct dev_exception_item *ex;
char maj[MAJMINLEN], min[MAJMINLEN], acc[ACCLEN];
rcu_read_lock();
- list_for_each_entry_rcu(wh, &devcgroup->whitelist, list) {
- set_access(acc, wh->access);
- set_majmin(maj, wh->major);
- set_majmin(min, wh->minor);
- seq_printf(m, "%c %s:%s %s\n", type_to_char(wh->type),
+ /*
+ * To preserve the compatibility:
+ * - Only show the "all devices" when the default policy is to allow
+ * - List the exceptions in case the default policy is to deny
+ * This way, the file remains as a "whitelist of devices"
+ */
+ if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+ set_access(acc, ACC_MASK);
+ set_majmin(maj, ~0);
+ set_majmin(min, ~0);
+ seq_printf(m, "%c %s:%s %s\n", type_to_char(DEV_ALL),
maj, min, acc);
+ } else {
+ list_for_each_entry_rcu(ex, &devcgroup->exceptions, list) {
+ set_access(acc, ex->access);
+ set_majmin(maj, ex->major);
+ set_majmin(min, ex->minor);
+ seq_printf(m, "%c %s:%s %s\n", type_to_char(ex->type),
+ maj, min, acc);
+ }
}
rcu_read_unlock();
return 0;
}
-/*
- * may_access_whitelist:
- * does the access granted to dev_cgroup c contain the access
- * requested in whitelist item refwh.
- * return 1 if yes, 0 if no.
- * call with devcgroup_mutex held
+/**
+ * may_access - verifies if a new exception is part of what is allowed
+ * by a dev cgroup based on the default policy +
+ * exceptions. This is used to make sure a child cgroup
+ * won't have more privileges than its parent or to
+ * verify if a certain access is allowed.
+ * @dev_cgroup: dev cgroup to be tested against
+ * @refex: new exception
*/
-static int may_access_whitelist(struct dev_cgroup *c,
- struct dev_whitelist_item *refwh)
+static int may_access(struct dev_cgroup *dev_cgroup,
+ struct dev_exception_item *refex)
{
- struct dev_whitelist_item *whitem;
+ struct dev_exception_item *ex;
+ bool match = false;
- list_for_each_entry(whitem, &c->whitelist, list) {
- if (whitem->type & DEV_ALL)
- return 1;
- if ((refwh->type & DEV_BLOCK) && !(whitem->type & DEV_BLOCK))
+ rcu_lockdep_assert(rcu_read_lock_held() ||
+ lockdep_is_held(&devcgroup_mutex),
+ "device_cgroup::may_access() called without proper synchronization");
+
+ list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) {
+ if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK))
continue;
- if ((refwh->type & DEV_CHAR) && !(whitem->type & DEV_CHAR))
+ if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))
continue;
- if (whitem->major != ~0 && whitem->major != refwh->major)
+ if (ex->major != ~0 && ex->major != refex->major)
continue;
- if (whitem->minor != ~0 && whitem->minor != refwh->minor)
+ if (ex->minor != ~0 && ex->minor != refex->minor)
continue;
- if (refwh->access & (~whitem->access))
+ if (refex->access & (~ex->access))
continue;
- return 1;
+ match = true;
+ break;
}
+
+ /*
+ * In two cases we'll consider this new exception valid:
+ * - the dev cgroup has its default policy to allow + exception list:
+ * the new exception should *not* match any of the exceptions
+ * (behavior == DEVCG_DEFAULT_ALLOW, !match)
+ * - the dev cgroup has its default policy to deny + exception list:
+ * the new exception *should* match the exceptions
+ * (behavior == DEVCG_DEFAULT_DENY, match)
+ */
+ if ((dev_cgroup->behavior == DEVCG_DEFAULT_DENY) == match)
+ return 1;
return 0;
}
/*
* parent_has_perm:
- * when adding a new allow rule to a device whitelist, the rule
+ * when adding a new allow rule to a device exception list, the rule
* must be allowed in the parent device
*/
static int parent_has_perm(struct dev_cgroup *childcg,
- struct dev_whitelist_item *wh)
+ struct dev_exception_item *ex)
{
struct cgroup *pcg = childcg->css.cgroup->parent;
struct dev_cgroup *parent;
@@ -309,17 +353,30 @@ static int parent_has_perm(struct dev_cgroup *childcg,
if (!pcg)
return 1;
parent = cgroup_to_devcgroup(pcg);
- return may_access_whitelist(parent, wh);
+ return may_access(parent, ex);
+}
+
+/**
+ * may_allow_all - checks if it's possible to change the behavior to
+ * allow based on parent's rules.
+ * @parent: device cgroup's parent
+ * returns: != 0 in case it's allowed, 0 otherwise
+ */
+static inline int may_allow_all(struct dev_cgroup *parent)
+{
+ if (!parent)
+ return 1;
+ return parent->behavior == DEVCG_DEFAULT_ALLOW;
}
/*
- * Modify the whitelist using allow/deny rules.
+ * Modify the exception list using allow/deny rules.
* CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
* so we can give a container CAP_MKNOD to let it create devices but not
- * modify the whitelist.
+ * modify the exception list.
* It seems likely we'll want to add a CAP_CONTAINER capability to allow
* us to also grant CAP_SYS_ADMIN to containers without giving away the
- * device whitelist controls, but for now we'll stick with CAP_SYS_ADMIN
+ * device exception list controls, but for now we'll stick with CAP_SYS_ADMIN
*
* Taking rules away is always allowed (given CAP_SYS_ADMIN). Granting
* new access is only allowed if you're in the top-level cgroup, or your
@@ -329,28 +386,50 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
int filetype, const char *buffer)
{
const char *b;
- char *endp;
- int count;
- struct dev_whitelist_item wh;
+ char temp[12]; /* 11 + 1 characters needed for a u32 */
+ int count, rc;
+ struct dev_exception_item ex;
+ struct cgroup *p = devcgroup->css.cgroup;
+ struct dev_cgroup *parent = NULL;
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
- memset(&wh, 0, sizeof(wh));
+ if (p->parent)
+ parent = cgroup_to_devcgroup(p->parent);
+
+ memset(&ex, 0, sizeof(ex));
b = buffer;
switch (*b) {
case 'a':
- wh.type = DEV_ALL;
- wh.access = ACC_MASK;
- wh.major = ~0;
- wh.minor = ~0;
- goto handle;
+ switch (filetype) {
+ case DEVCG_ALLOW:
+ if (!may_allow_all(parent))
+ return -EPERM;
+ dev_exception_clean(devcgroup);
+ devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
+ if (!parent)
+ break;
+
+ rc = dev_exceptions_copy(&devcgroup->exceptions,
+ &parent->exceptions);
+ if (rc)
+ return rc;
+ break;
+ case DEVCG_DENY:
+ dev_exception_clean(devcgroup);
+ devcgroup->behavior = DEVCG_DEFAULT_DENY;
+ break;
+ default:
+ return -EINVAL;
+ }
+ return 0;
case 'b':
- wh.type = DEV_BLOCK;
+ ex.type = DEV_BLOCK;
break;
case 'c':
- wh.type = DEV_CHAR;
+ ex.type = DEV_CHAR;
break;
default:
return -EINVAL;
@@ -360,11 +439,19 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
return -EINVAL;
b++;
if (*b == '*') {
- wh.major = ~0;
+ ex.major = ~0;
b++;
} else if (isdigit(*b)) {
- wh.major = simple_strtoul(b, &endp, 10);
- b = endp;
+ memset(temp, 0, sizeof(temp));
+ for (count = 0; count < sizeof(temp) - 1; count++) {
+ temp[count] = *b;
+ b++;
+ if (!isdigit(*b))
+ break;
+ }
+ rc = kstrtou32(temp, 10, &ex.major);
+ if (rc)
+ return -EINVAL;
} else {
return -EINVAL;
}
@@ -374,11 +461,19 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
/* read minor */
if (*b == '*') {
- wh.minor = ~0;
+ ex.minor = ~0;
b++;
} else if (isdigit(*b)) {
- wh.minor = simple_strtoul(b, &endp, 10);
- b = endp;
+ memset(temp, 0, sizeof(temp));
+ for (count = 0; count < sizeof(temp) - 1; count++) {
+ temp[count] = *b;
+ b++;
+ if (!isdigit(*b))
+ break;
+ }
+ rc = kstrtou32(temp, 10, &ex.minor);
+ if (rc)
+ return -EINVAL;
} else {
return -EINVAL;
}
@@ -387,13 +482,13 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
for (b++, count = 0; count < 3; count++, b++) {
switch (*b) {
case 'r':
- wh.access |= ACC_READ;
+ ex.access |= ACC_READ;
break;
case 'w':
- wh.access |= ACC_WRITE;
+ ex.access |= ACC_WRITE;
break;
case 'm':
- wh.access |= ACC_MKNOD;
+ ex.access |= ACC_MKNOD;
break;
case '\n':
case '\0':
@@ -404,15 +499,31 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
}
}
-handle:
switch (filetype) {
case DEVCG_ALLOW:
- if (!parent_has_perm(devcgroup, &wh))
+ if (!parent_has_perm(devcgroup, &ex))
return -EPERM;
- return dev_whitelist_add(devcgroup, &wh);
+ /*
+ * If the default policy is to allow by default, try to remove
+ * an matching exception instead. And be silent about it: we
+ * don't want to break compatibility
+ */
+ if (devcgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+ dev_exception_rm(devcgroup, &ex);
+ return 0;
+ }
+ return dev_exception_add(devcgroup, &ex);
case DEVCG_DENY:
- dev_whitelist_rm(devcgroup, &wh);
- break;
+ /*
+ * If the default policy is to deny by default, try to remove
+ * an matching exception instead. And be silent about it: we
+ * don't want to break compatibility
+ */
+ if (devcgroup->behavior == DEVCG_DEFAULT_DENY) {
+ dev_exception_rm(devcgroup, &ex);
+ return 0;
+ }
+ return dev_exception_add(devcgroup, &ex);
default:
return -EINVAL;
}
@@ -453,79 +564,85 @@ static struct cftype dev_cgroup_files[] = {
struct cgroup_subsys devices_subsys = {
.name = "devices",
.can_attach = devcgroup_can_attach,
- .create = devcgroup_create,
- .destroy = devcgroup_destroy,
+ .css_alloc = devcgroup_css_alloc,
+ .css_free = devcgroup_css_free,
.subsys_id = devices_subsys_id,
.base_cftypes = dev_cgroup_files,
+
+ /*
+ * While devices cgroup has the rudimentary hierarchy support which
+ * checks the parent's restriction, it doesn't properly propagates
+ * config changes in ancestors to their descendents. A child
+ * should only be allowed to add more restrictions to the parent's
+ * configuration. Fix it and remove the following.
+ */
+ .broken_hierarchy = true,
};
-int __devcgroup_inode_permission(struct inode *inode, int mask)
+/**
+ * __devcgroup_check_permission - checks if an inode operation is permitted
+ * @dev_cgroup: the dev cgroup to be tested against
+ * @type: device type
+ * @major: device major number
+ * @minor: device minor number
+ * @access: combination of ACC_WRITE, ACC_READ and ACC_MKNOD
+ *
+ * returns 0 on success, -EPERM case the operation is not permitted
+ */
+static int __devcgroup_check_permission(short type, u32 major, u32 minor,
+ short access)
{
struct dev_cgroup *dev_cgroup;
- struct dev_whitelist_item *wh;
+ struct dev_exception_item ex;
+ int rc;
- rcu_read_lock();
+ memset(&ex, 0, sizeof(ex));
+ ex.type = type;
+ ex.major = major;
+ ex.minor = minor;
+ ex.access = access;
+ rcu_read_lock();
dev_cgroup = task_devcgroup(current);
+ rc = may_access(dev_cgroup, &ex);
+ rcu_read_unlock();
- list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
- if (wh->type & DEV_ALL)
- goto found;
- if ((wh->type & DEV_BLOCK) && !S_ISBLK(inode->i_mode))
- continue;
- if ((wh->type & DEV_CHAR) && !S_ISCHR(inode->i_mode))
- continue;
- if (wh->major != ~0 && wh->major != imajor(inode))
- continue;
- if (wh->minor != ~0 && wh->minor != iminor(inode))
- continue;
-
- if ((mask & MAY_WRITE) && !(wh->access & ACC_WRITE))
- continue;
- if ((mask & MAY_READ) && !(wh->access & ACC_READ))
- continue;
-found:
- rcu_read_unlock();
- return 0;
- }
+ if (!rc)
+ return -EPERM;
- rcu_read_unlock();
+ return 0;
+}
- return -EPERM;
+int __devcgroup_inode_permission(struct inode *inode, int mask)
+{
+ short type, access = 0;
+
+ if (S_ISBLK(inode->i_mode))
+ type = DEV_BLOCK;
+ if (S_ISCHR(inode->i_mode))
+ type = DEV_CHAR;
+ if (mask & MAY_WRITE)
+ access |= ACC_WRITE;
+ if (mask & MAY_READ)
+ access |= ACC_READ;
+
+ return __devcgroup_check_permission(type, imajor(inode), iminor(inode),
+ access);
}
int devcgroup_inode_mknod(int mode, dev_t dev)
{
- struct dev_cgroup *dev_cgroup;
- struct dev_whitelist_item *wh;
+ short type;
if (!S_ISBLK(mode) && !S_ISCHR(mode))
return 0;
- rcu_read_lock();
-
- dev_cgroup = task_devcgroup(current);
-
- list_for_each_entry_rcu(wh, &dev_cgroup->whitelist, list) {
- if (wh->type & DEV_ALL)
- goto found;
- if ((wh->type & DEV_BLOCK) && !S_ISBLK(mode))
- continue;
- if ((wh->type & DEV_CHAR) && !S_ISCHR(mode))
- continue;
- if (wh->major != ~0 && wh->major != MAJOR(dev))
- continue;
- if (wh->minor != ~0 && wh->minor != MINOR(dev))
- continue;
-
- if (!(wh->access & ACC_MKNOD))
- continue;
-found:
- rcu_read_unlock();
- return 0;
- }
+ if (S_ISBLK(mode))
+ type = DEV_BLOCK;
+ else
+ type = DEV_CHAR;
- rcu_read_unlock();
+ return __devcgroup_check_permission(type, MAJOR(dev), MINOR(dev),
+ ACC_MKNOD);
- return -EPERM;
}
generated by cgit v1.2.3-70-g09d2 (git 2.46.0) at 2024-11-20 04:23:51 +0000