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selinux: saner handling of policy reloads 

On policy reload selinuxfs replaces two subdirectories (/booleans
and /class) with new variants.  Unfortunately, that's done with
serious abuses of directory locking.

1) lock_rename() should be done to parents, not to objects being
exchanged

2) there's a bunch of reasons why it should not be done for directories
that do not have a common ancestor; most of those do not apply to
selinuxfs, but even in the best case the proof is subtle and brittle.

3) failure halfway through the creation of /class will leak
names and values arrays.

4) use of d_genocide() is also rather brittle; it's probably not much of
a bug per se, but e.g. an overmount of /sys/fs/selinuxfs/classes/shm/index
with any regular file will end up with leaked mount on policy reload.
Sure, don't do it, but...

Let's stop messing with disconnected directories; just create
a temporary (/.swapover) with no permissions for anyone (on the
level of ->permission() returing -EPERM, no matter who's calling
it) and build the new /booleans and /class in there; then
lock_rename on root and that temporary directory and d_exchange()
old and new both for class and booleans.  Then unlock and use
simple_recursive_removal() to take the temporary out; it's much
more robust.

And instead of bothering with separate pathways for freeing
new (on failure halfway through) and old (on success) names/values,
do all freeing in one place.  With temporaries swapped with the
old ones when we are past all possible failures.

The only user-visible difference is that /.swapover shows up
(but isn't possible to open, look up into, etc.) for the
duration of policy reload.

Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
[PM: applied some fixes from Al post merge]
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Al Viro 2023-10-16 23:08:35 +01:00 committed by Paul Moore
parent b85ea95d08
commit 4a0b33f771
1 changed files with 68 additions and 80 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

148
security/selinux/selinuxfs.c
View File

@ -336,12 +336,9 @@ static struct dentry *sel_make_dir(struct dentry *dir, const char *name,
unsigned long *ino);
/* declaration for sel_make_policy_nodes */
static struct dentry *sel_make_disconnected_dir(struct super_block *sb,
static struct dentry *sel_make_swapover_dir(struct super_block *sb,
unsigned long *ino);
/* declaration for sel_make_policy_nodes */
static void sel_remove_entries(struct dentry *de);
static ssize_t sel_read_mls(struct file *filp, char __user *buf,
size_t count, loff_t *ppos)
{
@ -508,13 +505,13 @@ static int sel_make_policy_nodes(struct selinux_fs_info *fsi,
struct selinux_policy *newpolicy)
{
int ret = 0;
struct dentry *tmp_parent, *tmp_bool_dir, *tmp_class_dir, *old_dentry;
unsigned int tmp_bool_num, old_bool_num;
char **tmp_bool_names, **old_bool_names;
int *tmp_bool_values, *old_bool_values;
struct dentry *tmp_parent, *tmp_bool_dir, *tmp_class_dir;
unsigned int bool_num = 0;
char **bool_names = NULL;
int *bool_values = NULL;
unsigned long tmp_ino = fsi->last_ino; /* Don't increment last_ino in this function */
tmp_parent = sel_make_disconnected_dir(fsi->sb, &tmp_ino);
tmp_parent = sel_make_swapover_dir(fsi->sb, &tmp_ino);
if (IS_ERR(tmp_parent))
return PTR_ERR(tmp_parent);
@ -532,8 +529,8 @@ static int sel_make_policy_nodes(struct selinux_fs_info *fsi,
goto out;
}
ret = sel_make_bools(newpolicy, tmp_bool_dir, &tmp_bool_num,
&tmp_bool_names, &tmp_bool_values);
ret = sel_make_bools(newpolicy, tmp_bool_dir, &bool_num,
&bool_names, &bool_values);
if (ret)
goto out;
@ -542,38 +539,30 @@ static int sel_make_policy_nodes(struct selinux_fs_info *fsi,
if (ret)
goto out;
lock_rename(tmp_parent, fsi->sb->s_root);
/* booleans */
old_dentry = fsi->bool_dir;
lock_rename(tmp_bool_dir, old_dentry);
d_exchange(tmp_bool_dir, fsi->bool_dir);
old_bool_num = fsi->bool_num;
old_bool_names = fsi->bool_pending_names;
old_bool_values = fsi->bool_pending_values;
fsi->bool_num = tmp_bool_num;
fsi->bool_pending_names = tmp_bool_names;
fsi->bool_pending_values = tmp_bool_values;
sel_remove_old_bool_data(old_bool_num, old_bool_names, old_bool_values);
swap(fsi->bool_num, bool_num);
swap(fsi->bool_pending_names, bool_names);
swap(fsi->bool_pending_values, bool_values);
fsi->bool_dir = tmp_bool_dir;
unlock_rename(tmp_bool_dir, old_dentry);
/* classes */
old_dentry = fsi->class_dir;
lock_rename(tmp_class_dir, old_dentry);
d_exchange(tmp_class_dir, fsi->class_dir);
fsi->class_dir = tmp_class_dir;
unlock_rename(tmp_class_dir, old_dentry);
unlock_rename(tmp_parent, fsi->sb->s_root);
out:
sel_remove_old_bool_data(bool_num, bool_names, bool_values);
/* Since the other temporary dirs are children of tmp_parent
* this will handle all the cleanup in the case of a failure before
* the swapover
*/
sel_remove_entries(tmp_parent);
dput(tmp_parent); /* d_genocide() only handles the children */
simple_recursive_removal(tmp_parent, NULL);
return ret;
}
@ -1351,54 +1340,48 @@ static const struct file_operations sel_commit_bools_ops = {
.llseek = generic_file_llseek,
};
static void sel_remove_entries(struct dentry *de)
{
d_genocide(de);
shrink_dcache_parent(de);
}
static int sel_make_bools(struct selinux_policy *newpolicy, struct dentry *bool_dir,
unsigned int *bool_num, char ***bool_pending_names,
int **bool_pending_values)
{
int ret;
ssize_t len;
struct dentry *dentry = NULL;
struct inode *inode = NULL;
struct inode_security_struct *isec;
char **names = NULL, *page;
char **names, *page;
u32 i, num;
int *values = NULL;
u32 sid;
ret = -ENOMEM;
page = (char *)get_zeroed_page(GFP_KERNEL);
if (!page)
goto out;
return -ENOMEM;
ret = security_get_bools(newpolicy, &num, &names, &values);
ret = security_get_bools(newpolicy, &num, &names, bool_pending_values);
if (ret)
goto out;
for (i = 0; i < num; i++) {
ret = -ENOMEM;
dentry = d_alloc_name(bool_dir, names[i]);
if (!dentry)
goto out;
*bool_num = num;
*bool_pending_names = names;
for (i = 0; i < num; i++) {
struct dentry *dentry;
struct inode *inode;
struct inode_security_struct *isec;
ssize_t len;
u32 sid;
len = snprintf(page, PAGE_SIZE, "/%s/%s", BOOL_DIR_NAME, names[i]);
if (len >= PAGE_SIZE) {
ret = -ENAMETOOLONG;
break;
}
dentry = d_alloc_name(bool_dir, names[i]);
if (!dentry) {
ret = -ENOMEM;
break;
}
ret = -ENOMEM;
inode = sel_make_inode(bool_dir->d_sb, S_IFREG | S_IRUGO | S_IWUSR);
if (!inode) {
dput(dentry);
goto out;
}
ret = -ENAMETOOLONG;
len = snprintf(page, PAGE_SIZE, "/%s/%s", BOOL_DIR_NAME, names[i]);
if (len >= PAGE_SIZE) {
dput(dentry);
iput(inode);
goto out;
ret = -ENOMEM;
break;
}
isec = selinux_inode(inode);
@ -1416,23 +1399,8 @@ static int sel_make_bools(struct selinux_policy *newpolicy, struct dentry *bool_
inode->i_ino = i|SEL_BOOL_INO_OFFSET;
d_add(dentry, inode);
}
*bool_num = num;
*bool_pending_names = names;
*bool_pending_values = values;
free_page((unsigned long)page);
return 0;
out:
free_page((unsigned long)page);
if (names) {
for (i = 0; i < num; i++)
kfree(names[i]);
kfree(names);
}
kfree(values);
sel_remove_entries(bool_dir);
return ret;
}
@ -1961,20 +1929,40 @@ static struct dentry *sel_make_dir(struct dentry *dir, const char *name,
return dentry;
}
static struct dentry *sel_make_disconnected_dir(struct super_block *sb,
static int reject_all(struct mnt_idmap *idmap, struct inode *inode, int mask)
{
return -EPERM; // no access for anyone, root or no root.
}
static const struct inode_operations swapover_dir_inode_operations = {
.lookup = simple_lookup,
.permission = reject_all,
};
static struct dentry *sel_make_swapover_dir(struct super_block *sb,
unsigned long *ino)
{
struct inode *inode = sel_make_inode(sb, S_IFDIR | S_IRUGO | S_IXUGO);
struct dentry *dentry = d_alloc_name(sb->s_root, ".swapover");
struct inode *inode;
if (!inode)
if (!dentry)
return ERR_PTR(-ENOMEM);
inode->i_op = &simple_dir_inode_operations;
inode->i_fop = &simple_dir_operations;
inode = sel_make_inode(sb, S_IFDIR);
if (!inode) {
dput(dentry);
return ERR_PTR(-ENOMEM);
}
inode->i_op = &swapover_dir_inode_operations;
inode->i_ino = ++(*ino);
/* directory inodes start off with i_nlink == 2 (for "." entry) */
inc_nlink(inode);
return d_obtain_alias(inode);
inode_lock(sb->s_root->d_inode);
d_add(dentry, inode);
inc_nlink(sb->s_root->d_inode);
inode_unlock(sb->s_root->d_inode);
return dentry;
}
#define NULL_FILE_NAME "null"