Files
Karl Mehltretter 78fc54b934 selinux: recheck intermediate backing files on mprotect()
mprotect() can be used to bypass the SELinux checks that mmap() performs
against the intermediate layers of a stacked filesystem.

mmap() checks every backing layer as the request descends through the
stack.  mprotect() only has the lowest backing file in vma->vm_file, so it
rechecks the top-level user and the lowest mounter, but skips the mounters
of every layer in between.  With two nested overlayfs mounts and a policy
denying mounter_t -> middle_file_t:file { execute }, a direct
mmap(PROT_EXEC) is denied:

  avc:  denied  { execute } for  pid=71 comm="nested_exec"
    path="/payload" dev="overlay" ino=9
    scontext=user_u:base_r:mounter_t
    tcontext=user_u:object_r:middle_file_t tclass=file permissive=0

while mmap(PROT_NONE) followed by mprotect(PROT_EXEC) succeeds.

Preserve each intermediate path, mounter SID and file-description SID in
the backing-file security blob, copying the saved entries when another
backing layer is opened.  Allocate the array only for nested backing files,
and release it and the path references in the backing_file_free hook.

During mprotect(), recheck fd { use } and the requested inode permissions
for every saved mounter, and include the intermediate layers in the execmod
checks.  Policy for nested stacking may then need to grant intermediate
mounters what a direct mmap() already requires, and execmod on intermediate
labels for binaries using text relocations.

Tested on arm64 QEMU with a small BusyBox initramfs and a purpose-built
SELinux policy, on a mainline tree containing
commit f2381b546e ("fs: fix user path of nested backing files").

Cc: [email protected]
Fixes: 82544d36b1 ("selinux: fix overlayfs mmap() and mprotect() access checks")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <[email protected]>
Reviewed-by: Stephen Smalley <[email protected]>
[PM: subject tweak]
Signed-off-by: Paul Moore <[email protected]>
2026-09-15 23:30:07 -04:00

299 lines
7.9 KiB
C

/* SPDX-License-Identifier: GPL-2.0-only */
/*
* Security-Enhanced Linux (SELinux) security module
*
* This file contains the SELinux security data structures for kernel objects.
*
* Author(s): Stephen Smalley, <[email protected]>
* Chris Vance, <[email protected]>
* Wayne Salamon, <[email protected]>
* James Morris <[email protected]>
*
* Copyright (C) 2001,2002 Networks Associates Technology, Inc.
* Copyright (C) 2003 Red Hat, Inc., James Morris <[email protected]>
* Copyright (C) 2016 Mellanox Technologies
*/
#ifndef _SELINUX_OBJSEC_H_
#define _SELINUX_OBJSEC_H_
#include <linux/list.h>
#include <linux/sched.h>
#include <linux/fs.h>
#include <linux/binfmts.h>
#include <linux/in.h>
#include <linux/spinlock.h>
#include <linux/lsm_hooks.h>
#include <linux/msg.h>
#include <net/net_namespace.h>
#include <linux/bpf.h>
#include "flask.h"
#include "avc.h"
struct avdc_entry {
u32 isid; /* inode SID */
struct av_decision avd; /* av decision */
};
struct cred_security_struct {
u32 osid; /* SID prior to last execve */
u32 sid; /* current SID */
u32 exec_sid; /* exec SID */
u32 create_sid; /* fscreate SID */
u32 keycreate_sid; /* keycreate SID */
u32 sockcreate_sid; /* fscreate SID */
} __randomize_layout;
struct task_security_struct {
#define TSEC_AVDC_DIR_SIZE (1 << 2)
struct {
u32 sid; /* current SID for cached entries */
u32 seqno; /* AVC sequence number */
unsigned int dir_spot; /* dir cache index to check first */
struct avdc_entry dir[TSEC_AVDC_DIR_SIZE]; /* dir entries */
bool permissive_neveraudit; /* permissive and neveraudit */
} avdcache;
} __randomize_layout;
static inline bool task_avdcache_permnoaudit(struct task_security_struct *tsec,
u32 sid)
{
return (tsec->avdcache.permissive_neveraudit &&
sid == tsec->avdcache.sid &&
tsec->avdcache.seqno == avc_policy_seqno());
}
enum label_initialized {
LABEL_INVALID, /* invalid or not initialized */
LABEL_INITIALIZED, /* initialized */
LABEL_PENDING
};
struct inode_security_struct {
struct inode *inode; /* back pointer to inode object */
struct list_head list; /* list of inode_security_struct */
u32 task_sid; /* SID of creating task */
u32 sid; /* SID of this object */
u16 sclass; /* security class of this object */
unsigned char initialized; /* initialization flag */
spinlock_t lock;
};
struct file_security_struct {
u32 sid; /* SID of open file description */
u32 fown_sid; /* SID of file owner (for SIGIO) */
u32 isid; /* SID of inode at the time of file open */
u32 pseqno; /* Policy seqno at the time of file open */
};
struct backing_file_security_layer {
struct path path; /* this layer's real path */
u32 mounter_sid; /* SID of the mounter that opened it */
u32 fd_sid; /* SID of its open file description */
};
struct backing_file_security_struct {
u32 uf_sid; /* top-level user file fsec->sid */
u32 layer_count; /* number of intermediate backing files */
struct backing_file_security_layer *layers;
};
struct superblock_security_struct {
u32 sid; /* SID of file system superblock */
u32 def_sid; /* default SID for labeling */
u32 mntpoint_sid; /* SECURITY_FS_USE_MNTPOINT context for files */
u32 creator_sid; /* SID of privileged process */
unsigned short behavior; /* labeling behavior */
unsigned short flags; /* which mount options were specified */
struct mutex lock;
struct list_head isec_head;
spinlock_t isec_lock;
};
struct msg_security_struct {
u32 sid; /* SID of message */
};
struct ipc_security_struct {
u16 sclass; /* security class of this object */
u32 sid; /* SID of IPC resource */
};
struct netif_security_struct {
const struct net *ns; /* network namespace */
int ifindex; /* device index */
u32 sid; /* SID for this interface */
};
struct netnode_security_struct {
union {
__be32 ipv4; /* IPv4 node address */
struct in6_addr ipv6; /* IPv6 node address */
} addr;
u32 sid; /* SID for this node */
u16 family; /* address family */
};
struct netport_security_struct {
u32 sid; /* SID for this node */
u16 port; /* port number */
u8 protocol; /* transport protocol */
};
struct sk_security_struct {
#ifdef CONFIG_NETLABEL
enum { /* NetLabel state */
NLBL_UNSET = 0,
NLBL_REQUIRE,
NLBL_LABELED,
NLBL_REQSKB,
NLBL_CONNLABELED,
} nlbl_state;
struct netlbl_lsm_secattr *nlbl_secattr; /* NetLabel sec attributes */
#endif
u32 sid; /* SID of this object */
u32 peer_sid; /* SID of peer */
u16 sclass; /* sock security class */
enum { /* SCTP association state */
SCTP_ASSOC_UNSET = 0,
SCTP_ASSOC_SET,
} sctp_assoc_state;
};
struct tun_security_struct {
u32 sid; /* SID for the tun device sockets */
};
struct key_security_struct {
u32 sid; /* SID of key */
};
struct ib_security_struct {
u32 sid; /* SID of the queue pair or MAD agent */
};
struct pkey_security_struct {
u64 subnet_prefix; /* Port subnet prefix */
u16 pkey; /* PKey number */
u32 sid; /* SID of pkey */
};
struct bpf_security_struct {
u32 sid; /* SID of bpf obj creator */
u32 perms; /* permissions for allowed bpf token commands */
u32 grantor_sid; /* SID of token grantor */
};
struct perf_event_security_struct {
u32 sid; /* SID of perf_event obj creator */
};
extern struct lsm_blob_sizes selinux_blob_sizes;
static inline struct cred_security_struct *selinux_cred(const struct cred *cred)
{
return cred->security + selinux_blob_sizes.lbs_cred;
}
static inline struct task_security_struct *
selinux_task(const struct task_struct *task)
{
return task->security + selinux_blob_sizes.lbs_task;
}
static inline struct file_security_struct *selinux_file(const struct file *file)
{
return file->f_security + selinux_blob_sizes.lbs_file;
}
static inline struct backing_file_security_struct *
selinux_backing_file(const struct file *backing_file)
{
void *blob = backing_file_security(backing_file);
return blob + selinux_blob_sizes.lbs_backing_file;
}
static inline struct inode_security_struct *
selinux_inode(const struct inode *inode)
{
if (unlikely(!inode->i_security))
return NULL;
return inode->i_security + selinux_blob_sizes.lbs_inode;
}
static inline struct msg_security_struct *
selinux_msg_msg(const struct msg_msg *msg_msg)
{
return msg_msg->security + selinux_blob_sizes.lbs_msg_msg;
}
static inline struct ipc_security_struct *
selinux_ipc(const struct kern_ipc_perm *ipc)
{
return ipc->security + selinux_blob_sizes.lbs_ipc;
}
/*
* get the subjective security ID of the current task
*/
static inline u32 current_sid(void)
{
const struct cred_security_struct *crsec = selinux_cred(current_cred());
return crsec->sid;
}
static inline struct superblock_security_struct *
selinux_superblock(const struct super_block *superblock)
{
return superblock->s_security + selinux_blob_sizes.lbs_superblock;
}
#ifdef CONFIG_KEYS
static inline struct key_security_struct *selinux_key(const struct key *key)
{
return key->security + selinux_blob_sizes.lbs_key;
}
#endif /* CONFIG_KEYS */
static inline struct sk_security_struct *selinux_sock(const struct sock *sock)
{
return sock->sk_security + selinux_blob_sizes.lbs_sock;
}
static inline struct tun_security_struct *selinux_tun_dev(void *security)
{
return security + selinux_blob_sizes.lbs_tun_dev;
}
static inline struct ib_security_struct *selinux_ib(void *ib_sec)
{
return ib_sec + selinux_blob_sizes.lbs_ib;
}
static inline struct perf_event_security_struct *
selinux_perf_event(void *perf_event)
{
return perf_event + selinux_blob_sizes.lbs_perf_event;
}
#ifdef CONFIG_BPF_SYSCALL
static inline struct bpf_security_struct *
selinux_bpf_map_security(struct bpf_map *map)
{
return map->security + selinux_blob_sizes.lbs_bpf_map;
}
static inline struct bpf_security_struct *
selinux_bpf_prog_security(struct bpf_prog *prog)
{
return prog->aux->security + selinux_blob_sizes.lbs_bpf_prog;
}
static inline struct bpf_security_struct *
selinux_bpf_token_security(struct bpf_token *token)
{
return token->security + selinux_blob_sizes.lbs_bpf_token;
}
#endif /* CONFIG_BPF_SYSCALL */
#endif /* _SELINUX_OBJSEC_H_ */