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selinux: allow multiple opens of /sys/fs/selinux/policy

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Currently there can only be a single open of /sys/fs/selinux/policy at
any time. This allows any process to block any other process from
reading the kernel policy. The original motivation seems to have been
a mix of preventing an inconsistent view of the policy size and
preventing userspace from allocating kernel memory without bound, but
this is arguably equally bad. Eliminate the policy_opened flag and
shrink the critical section that the policy mutex is held. While we
are making changes here, drop a couple of extraneous BUG_ONs.

Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/selinux/20100726193414.19538.64028.stgit@paris.rdu.redhat.com/
Signed-off-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
This commit is contained in:
Stephen Smalley 2026-05-05 10:06:38 -04:00 committed by Paul Moore
parent ad1ac3d740
commit a02cd68055
1 changed files with 4 additions and 23 deletions
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27
security/selinux/selinuxfs.c
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@ -76,7 +76,6 @@ struct selinux_fs_info {
int *bool_pending_values;
struct dentry *class_dir;
unsigned long last_class_ino;
bool policy_opened;
unsigned long last_ino;
struct super_block *sb;
};
@ -340,44 +339,31 @@ struct policy_load_memory {
static int sel_open_policy(struct inode *inode, struct file *filp)
{
struct selinux_fs_info *fsi = inode->i_sb->s_fs_info;
struct policy_load_memory *plm = NULL;
int rc;
BUG_ON(filp->private_data);
mutex_lock(&selinux_state.policy_mutex);
rc = avc_has_perm(current_sid(), SECINITSID_SECURITY,
SECCLASS_SECURITY, SECURITY__READ_POLICY, NULL);
if (rc)
goto err;
return rc;
rc = -EBUSY;
if (fsi->policy_opened)
goto err;
rc = -ENOMEM;
plm = kzalloc_obj(*plm);
if (!plm)
goto err;
return -ENOMEM;
mutex_lock(&selinux_state.policy_mutex);
rc = security_read_policy(&plm->data, &plm->len);
if (rc)
goto err;
if ((size_t)i_size_read(inode) != plm->len) {
inode_lock(inode);
i_size_write(inode, plm->len);
inode_unlock(inode);
}
fsi->policy_opened = 1;
mutex_unlock(&selinux_state.policy_mutex);
filp->private_data = plm;
mutex_unlock(&selinux_state.policy_mutex);
return 0;
err:
mutex_unlock(&selinux_state.policy_mutex);
@ -390,13 +376,8 @@ static int sel_open_policy(struct inode *inode, struct file *filp)
static int sel_release_policy(struct inode *inode, struct file *filp)
{
struct selinux_fs_info *fsi = inode->i_sb->s_fs_info;
struct policy_load_memory *plm = filp->private_data;
BUG_ON(!plm);
fsi->policy_opened = 0;
vfree(plm->data);
kfree(plm);