blob: 68fa225f89e54d10af16e5a9fb94a109ea556507 [file] [log] [blame]
// SPDX-License-Identifier: GPL-2.0-only
/*
* binfmt_misc.c
*
* Copyright (C) 1997 Richard G√ľnther
*
* binfmt_misc detects binaries via a magic or filename extension and invokes
* a specified wrapper. See Documentation/admin-guide/binfmt-misc.rst for more details.
*/
#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/sched/mm.h>
#include <linux/magic.h>
#include <linux/binfmts.h>
#include <linux/slab.h>
#include <linux/ctype.h>
#include <linux/string_helpers.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/fs_context.h>
#include <linux/syscalls.h>
#include <linux/fs.h>
#include <linux/uaccess.h>
#include "internal.h"
#ifdef DEBUG
# define USE_DEBUG 1
#else
# define USE_DEBUG 0
#endif
enum {
VERBOSE_STATUS = 1 /* make it zero to save 400 bytes kernel memory */
};
enum {Enabled, Magic};
#define MISC_FMT_PRESERVE_ARGV0 (1UL << 31)
#define MISC_FMT_OPEN_BINARY (1UL << 30)
#define MISC_FMT_CREDENTIALS (1UL << 29)
#define MISC_FMT_OPEN_FILE (1UL << 28)
typedef struct {
struct list_head list;
unsigned long flags; /* type, status, etc. */
int offset; /* offset of magic */
int size; /* size of magic/mask */
char *magic; /* magic or filename extension */
char *mask; /* mask, NULL for exact match */
const char *interpreter; /* filename of interpreter */
char *name;
struct dentry *dentry;
struct file *interp_file;
refcount_t users; /* sync removal with load_misc_binary() */
} Node;
static struct file_system_type bm_fs_type;
/*
* Max length of the register string. Determined by:
* - 7 delimiters
* - name: ~50 bytes
* - type: 1 byte
* - offset: 3 bytes (has to be smaller than BINPRM_BUF_SIZE)
* - magic: 128 bytes (512 in escaped form)
* - mask: 128 bytes (512 in escaped form)
* - interp: ~50 bytes
* - flags: 5 bytes
* Round that up a bit, and then back off to hold the internal data
* (like struct Node).
*/
#define MAX_REGISTER_LENGTH 1920
/**
* search_binfmt_handler - search for a binary handler for @bprm
* @misc: handle to binfmt_misc instance
* @bprm: binary for which we are looking for a handler
*
* Search for a binary type handler for @bprm in the list of registered binary
* type handlers.
*
* Return: binary type list entry on success, NULL on failure
*/
static Node *search_binfmt_handler(struct binfmt_misc *misc,
struct linux_binprm *bprm)
{
char *p = strrchr(bprm->interp, '.');
Node *e;
/* Walk all the registered handlers. */
list_for_each_entry(e, &misc->entries, list) {
char *s;
int j;
/* Make sure this one is currently enabled. */
if (!test_bit(Enabled, &e->flags))
continue;
/* Do matching based on extension if applicable. */
if (!test_bit(Magic, &e->flags)) {
if (p && !strcmp(e->magic, p + 1))
return e;
continue;
}
/* Do matching based on magic & mask. */
s = bprm->buf + e->offset;
if (e->mask) {
for (j = 0; j < e->size; j++)
if ((*s++ ^ e->magic[j]) & e->mask[j])
break;
} else {
for (j = 0; j < e->size; j++)
if ((*s++ ^ e->magic[j]))
break;
}
if (j == e->size)
return e;
}
return NULL;
}
/**
* get_binfmt_handler - try to find a binary type handler
* @misc: handle to binfmt_misc instance
* @bprm: binary for which we are looking for a handler
*
* Try to find a binfmt handler for the binary type. If one is found take a
* reference to protect against removal via bm_{entry,status}_write().
*
* Return: binary type list entry on success, NULL on failure
*/
static Node *get_binfmt_handler(struct binfmt_misc *misc,
struct linux_binprm *bprm)
{
Node *e;
read_lock(&misc->entries_lock);
e = search_binfmt_handler(misc, bprm);
if (e)
refcount_inc(&e->users);
read_unlock(&misc->entries_lock);
return e;
}
/**
* put_binfmt_handler - put binary handler node
* @e: node to put
*
* Free node syncing with load_misc_binary() and defer final free to
* load_misc_binary() in case it is using the binary type handler we were
* requested to remove.
*/
static void put_binfmt_handler(Node *e)
{
if (refcount_dec_and_test(&e->users)) {
if (e->flags & MISC_FMT_OPEN_FILE)
filp_close(e->interp_file, NULL);
kfree(e);
}
}
/**
* load_binfmt_misc - load the binfmt_misc of the caller's user namespace
*
* To be called in load_misc_binary() to load the relevant struct binfmt_misc.
* If a user namespace doesn't have its own binfmt_misc mount it can make use
* of its ancestor's binfmt_misc handlers. This mimicks the behavior of
* pre-namespaced binfmt_misc where all registered binfmt_misc handlers where
* available to all user and user namespaces on the system.
*
* Return: the binfmt_misc instance of the caller's user namespace
*/
static struct binfmt_misc *load_binfmt_misc(void)
{
const struct user_namespace *user_ns;
struct binfmt_misc *misc;
user_ns = current_user_ns();
while (user_ns) {
/* Pairs with smp_store_release() in bm_fill_super(). */
misc = smp_load_acquire(&user_ns->binfmt_misc);
if (misc)
return misc;
user_ns = user_ns->parent;
}
return &init_binfmt_misc;
}
/*
* the loader itself
*/
static int load_misc_binary(struct linux_binprm *bprm)
{
Node *fmt;
struct file *interp_file = NULL;
int retval = -ENOEXEC;
struct binfmt_misc *misc;
misc = load_binfmt_misc();
if (!misc->enabled)
return retval;
fmt = get_binfmt_handler(misc, bprm);
if (!fmt)
return retval;
/* Need to be able to load the file after exec */
retval = -ENOENT;
if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
goto ret;
if (fmt->flags & MISC_FMT_PRESERVE_ARGV0) {
bprm->interp_flags |= BINPRM_FLAGS_PRESERVE_ARGV0;
} else {
retval = remove_arg_zero(bprm);
if (retval)
goto ret;
}
if (fmt->flags & MISC_FMT_OPEN_BINARY)
bprm->have_execfd = 1;
/* make argv[1] be the path to the binary */
retval = copy_string_kernel(bprm->interp, bprm);
if (retval < 0)
goto ret;
bprm->argc++;
/* add the interp as argv[0] */
retval = copy_string_kernel(fmt->interpreter, bprm);
if (retval < 0)
goto ret;
bprm->argc++;
/* Update interp in case binfmt_script needs it. */
retval = bprm_change_interp(fmt->interpreter, bprm);
if (retval < 0)
goto ret;
if (fmt->flags & MISC_FMT_OPEN_FILE) {
interp_file = file_clone_open(fmt->interp_file);
if (!IS_ERR(interp_file))
deny_write_access(interp_file);
} else {
interp_file = open_exec(fmt->interpreter);
}
retval = PTR_ERR(interp_file);
if (IS_ERR(interp_file))
goto ret;
bprm->interpreter = interp_file;
if (fmt->flags & MISC_FMT_CREDENTIALS)
bprm->execfd_creds = 1;
retval = 0;
ret:
/*
* If we actually put the node here all concurrent calls to
* load_misc_binary() will have finished. We also know
* that for the refcount to be zero someone must have concurently
* removed the binary type handler from the list and it's our job to
* free it.
*/
put_binfmt_handler(fmt);
return retval;
}
/* Command parsers */
/*
* parses and copies one argument enclosed in del from *sp to *dp,
* recognising the \x special.
* returns pointer to the copied argument or NULL in case of an
* error (and sets err) or null argument length.
*/
static char *scanarg(char *s, char del)
{
char c;
while ((c = *s++) != del) {
if (c == '\\' && *s == 'x') {
s++;
if (!isxdigit(*s++))
return NULL;
if (!isxdigit(*s++))
return NULL;
}
}
s[-1] ='\0';
return s;
}
static char *check_special_flags(char *sfs, Node *e)
{
char *p = sfs;
int cont = 1;
/* special flags */
while (cont) {
switch (*p) {
case 'P':
pr_debug("register: flag: P (preserve argv0)\n");
p++;
e->flags |= MISC_FMT_PRESERVE_ARGV0;
break;
case 'O':
pr_debug("register: flag: O (open binary)\n");
p++;
e->flags |= MISC_FMT_OPEN_BINARY;
break;
case 'C':
pr_debug("register: flag: C (preserve creds)\n");
p++;
/* this flags also implies the
open-binary flag */
e->flags |= (MISC_FMT_CREDENTIALS |
MISC_FMT_OPEN_BINARY);
break;
case 'F':
pr_debug("register: flag: F: open interpreter file now\n");
p++;
e->flags |= MISC_FMT_OPEN_FILE;
break;
default:
cont = 0;
}
}
return p;
}
/*
* This registers a new binary format, it recognises the syntax
* ':name:type:offset:magic:mask:interpreter:flags'
* where the ':' is the IFS, that can be chosen with the first char
*/
static Node *create_entry(const char __user *buffer, size_t count)
{
Node *e;
int memsize, err;
char *buf, *p;
char del;
pr_debug("register: received %zu bytes\n", count);
/* some sanity checks */
err = -EINVAL;
if ((count < 11) || (count > MAX_REGISTER_LENGTH))
goto out;
err = -ENOMEM;
memsize = sizeof(Node) + count + 8;
e = kmalloc(memsize, GFP_KERNEL_ACCOUNT);
if (!e)
goto out;
p = buf = (char *)e + sizeof(Node);
memset(e, 0, sizeof(Node));
if (copy_from_user(buf, buffer, count))
goto efault;
del = *p++; /* delimeter */
pr_debug("register: delim: %#x {%c}\n", del, del);
/* Pad the buffer with the delim to simplify parsing below. */
memset(buf + count, del, 8);
/* Parse the 'name' field. */
e->name = p;
p = strchr(p, del);
if (!p)
goto einval;
*p++ = '\0';
if (!e->name[0] ||
!strcmp(e->name, ".") ||
!strcmp(e->name, "..") ||
strchr(e->name, '/'))
goto einval;
pr_debug("register: name: {%s}\n", e->name);
/* Parse the 'type' field. */
switch (*p++) {
case 'E':
pr_debug("register: type: E (extension)\n");
e->flags = 1 << Enabled;
break;
case 'M':
pr_debug("register: type: M (magic)\n");
e->flags = (1 << Enabled) | (1 << Magic);
break;
default:
goto einval;
}
if (*p++ != del)
goto einval;
if (test_bit(Magic, &e->flags)) {
/* Handle the 'M' (magic) format. */
char *s;
/* Parse the 'offset' field. */
s = strchr(p, del);
if (!s)
goto einval;
*s = '\0';
if (p != s) {
int r = kstrtoint(p, 10, &e->offset);
if (r != 0 || e->offset < 0)
goto einval;
}
p = s;
if (*p++)
goto einval;
pr_debug("register: offset: %#x\n", e->offset);
/* Parse the 'magic' field. */
e->magic = p;
p = scanarg(p, del);
if (!p)
goto einval;
if (!e->magic[0])
goto einval;
if (USE_DEBUG)
print_hex_dump_bytes(
KBUILD_MODNAME ": register: magic[raw]: ",
DUMP_PREFIX_NONE, e->magic, p - e->magic);
/* Parse the 'mask' field. */
e->mask = p;
p = scanarg(p, del);
if (!p)
goto einval;
if (!e->mask[0]) {
e->mask = NULL;
pr_debug("register: mask[raw]: none\n");
} else if (USE_DEBUG)
print_hex_dump_bytes(
KBUILD_MODNAME ": register: mask[raw]: ",
DUMP_PREFIX_NONE, e->mask, p - e->mask);
/*
* Decode the magic & mask fields.
* Note: while we might have accepted embedded NUL bytes from
* above, the unescape helpers here will stop at the first one
* it encounters.
*/
e->size = string_unescape_inplace(e->magic, UNESCAPE_HEX);
if (e->mask &&
string_unescape_inplace(e->mask, UNESCAPE_HEX) != e->size)
goto einval;
if (e->size > BINPRM_BUF_SIZE ||
BINPRM_BUF_SIZE - e->size < e->offset)
goto einval;
pr_debug("register: magic/mask length: %i\n", e->size);
if (USE_DEBUG) {
print_hex_dump_bytes(
KBUILD_MODNAME ": register: magic[decoded]: ",
DUMP_PREFIX_NONE, e->magic, e->size);
if (e->mask) {
int i;
char *masked = kmalloc(e->size, GFP_KERNEL_ACCOUNT);
print_hex_dump_bytes(
KBUILD_MODNAME ": register: mask[decoded]: ",
DUMP_PREFIX_NONE, e->mask, e->size);
if (masked) {
for (i = 0; i < e->size; ++i)
masked[i] = e->magic[i] & e->mask[i];
print_hex_dump_bytes(
KBUILD_MODNAME ": register: magic[masked]: ",
DUMP_PREFIX_NONE, masked, e->size);
kfree(masked);
}
}
}
} else {
/* Handle the 'E' (extension) format. */
/* Skip the 'offset' field. */
p = strchr(p, del);
if (!p)
goto einval;
*p++ = '\0';
/* Parse the 'magic' field. */
e->magic = p;
p = strchr(p, del);
if (!p)
goto einval;
*p++ = '\0';
if (!e->magic[0] || strchr(e->magic, '/'))
goto einval;
pr_debug("register: extension: {%s}\n", e->magic);
/* Skip the 'mask' field. */
p = strchr(p, del);
if (!p)
goto einval;
*p++ = '\0';
}
/* Parse the 'interpreter' field. */
e->interpreter = p;
p = strchr(p, del);
if (!p)
goto einval;
*p++ = '\0';
if (!e->interpreter[0])
goto einval;
pr_debug("register: interpreter: {%s}\n", e->interpreter);
/* Parse the 'flags' field. */
p = check_special_flags(p, e);
if (*p == '\n')
p++;
if (p != buf + count)
goto einval;
return e;
out:
return ERR_PTR(err);
efault:
kfree(e);
return ERR_PTR(-EFAULT);
einval:
kfree(e);
return ERR_PTR(-EINVAL);
}
/*
* Set status of entry/binfmt_misc:
* '1' enables, '0' disables and '-1' clears entry/binfmt_misc
*/
static int parse_command(const char __user *buffer, size_t count)
{
char s[4];
if (count > 3)
return -EINVAL;
if (copy_from_user(s, buffer, count))
return -EFAULT;
if (!count)
return 0;
if (s[count - 1] == '\n')
count--;
if (count == 1 && s[0] == '0')
return 1;
if (count == 1 && s[0] == '1')
return 2;
if (count == 2 && s[0] == '-' && s[1] == '1')
return 3;
return -EINVAL;
}
/* generic stuff */
static void entry_status(Node *e, char *page)
{
char *dp = page;
const char *status = "disabled";
if (test_bit(Enabled, &e->flags))
status = "enabled";
if (!VERBOSE_STATUS) {
sprintf(page, "%s\n", status);
return;
}
dp += sprintf(dp, "%s\ninterpreter %s\n", status, e->interpreter);
/* print the special flags */
dp += sprintf(dp, "flags: ");
if (e->flags & MISC_FMT_PRESERVE_ARGV0)
*dp++ = 'P';
if (e->flags & MISC_FMT_OPEN_BINARY)
*dp++ = 'O';
if (e->flags & MISC_FMT_CREDENTIALS)
*dp++ = 'C';
if (e->flags & MISC_FMT_OPEN_FILE)
*dp++ = 'F';
*dp++ = '\n';
if (!test_bit(Magic, &e->flags)) {
sprintf(dp, "extension .%s\n", e->magic);
} else {
dp += sprintf(dp, "offset %i\nmagic ", e->offset);
dp = bin2hex(dp, e->magic, e->size);
if (e->mask) {
dp += sprintf(dp, "\nmask ");
dp = bin2hex(dp, e->mask, e->size);
}
*dp++ = '\n';
*dp = '\0';
}
}
static struct inode *bm_get_inode(struct super_block *sb, int mode)
{
struct inode *inode = new_inode(sb);
if (inode) {
inode->i_ino = get_next_ino();
inode->i_mode = mode;
simple_inode_init_ts(inode);
}
return inode;
}
/**
* i_binfmt_misc - retrieve struct binfmt_misc from a binfmt_misc inode
* @inode: inode of the relevant binfmt_misc instance
*
* This helper retrieves struct binfmt_misc from a binfmt_misc inode. This can
* be done without any memory barriers because we are guaranteed that
* user_ns->binfmt_misc is fully initialized. It was fully initialized when the
* binfmt_misc mount was first created.
*
* Return: struct binfmt_misc of the relevant binfmt_misc instance
*/
static struct binfmt_misc *i_binfmt_misc(struct inode *inode)
{
return inode->i_sb->s_user_ns->binfmt_misc;
}
/**
* bm_evict_inode - cleanup data associated with @inode
* @inode: inode to which the data is attached
*
* Cleanup the binary type handler data associated with @inode if a binary type
* entry is removed or the filesystem is unmounted and the super block is
* shutdown.
*
* If the ->evict call was not caused by a super block shutdown but by a write
* to remove the entry or all entries via bm_{entry,status}_write() the entry
* will have already been removed from the list. We keep the list_empty() check
* to make that explicit.
*/
static void bm_evict_inode(struct inode *inode)
{
Node *e = inode->i_private;
clear_inode(inode);
if (e) {
struct binfmt_misc *misc;
misc = i_binfmt_misc(inode);
write_lock(&misc->entries_lock);
if (!list_empty(&e->list))
list_del_init(&e->list);
write_unlock(&misc->entries_lock);
put_binfmt_handler(e);
}
}
/**
* unlink_binfmt_dentry - remove the dentry for the binary type handler
* @dentry: dentry associated with the binary type handler
*
* Do the actual filesystem work to remove a dentry for a registered binary
* type handler. Since binfmt_misc only allows simple files to be created
* directly under the root dentry of the filesystem we ensure that we are
* indeed passed a dentry directly beneath the root dentry, that the inode
* associated with the root dentry is locked, and that it is a regular file we
* are asked to remove.
*/
static void unlink_binfmt_dentry(struct dentry *dentry)
{
struct dentry *parent = dentry->d_parent;
struct inode *inode, *parent_inode;
/* All entries are immediate descendants of the root dentry. */
if (WARN_ON_ONCE(dentry->d_sb->s_root != parent))
return;
/* We only expect to be called on regular files. */
inode = d_inode(dentry);
if (WARN_ON_ONCE(!S_ISREG(inode->i_mode)))
return;
/* The parent inode must be locked. */
parent_inode = d_inode(parent);
if (WARN_ON_ONCE(!inode_is_locked(parent_inode)))
return;
if (simple_positive(dentry)) {
dget(dentry);
simple_unlink(parent_inode, dentry);
d_delete(dentry);
dput(dentry);
}
}
/**
* remove_binfmt_handler - remove a binary type handler
* @misc: handle to binfmt_misc instance
* @e: binary type handler to remove
*
* Remove a binary type handler from the list of binary type handlers and
* remove its associated dentry. This is called from
* binfmt_{entry,status}_write(). In the future, we might want to think about
* adding a proper ->unlink() method to binfmt_misc instead of forcing caller's
* to use writes to files in order to delete binary type handlers. But it has
* worked for so long that it's not a pressing issue.
*/
static void remove_binfmt_handler(struct binfmt_misc *misc, Node *e)
{
write_lock(&misc->entries_lock);
list_del_init(&e->list);
write_unlock(&misc->entries_lock);
unlink_binfmt_dentry(e->dentry);
}
/* /<entry> */
static ssize_t
bm_entry_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
Node *e = file_inode(file)->i_private;
ssize_t res;
char *page;
page = (char *) __get_free_page(GFP_KERNEL);
if (!page)
return -ENOMEM;
entry_status(e, page);
res = simple_read_from_buffer(buf, nbytes, ppos, page, strlen(page));
free_page((unsigned long) page);
return res;
}
static ssize_t bm_entry_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
struct inode *inode = file_inode(file);
Node *e = inode->i_private;
int res = parse_command(buffer, count);
switch (res) {
case 1:
/* Disable this handler. */
clear_bit(Enabled, &e->flags);
break;
case 2:
/* Enable this handler. */
set_bit(Enabled, &e->flags);
break;
case 3:
/* Delete this handler. */
inode = d_inode(inode->i_sb->s_root);
inode_lock(inode);
/*
* In order to add new element or remove elements from the list
* via bm_{entry,register,status}_write() inode_lock() on the
* root inode must be held.
* The lock is exclusive ensuring that the list can't be
* modified. Only load_misc_binary() can access but does so
* read-only. So we only need to take the write lock when we
* actually remove the entry from the list.
*/
if (!list_empty(&e->list))
remove_binfmt_handler(i_binfmt_misc(inode), e);
inode_unlock(inode);
break;
default:
return res;
}
return count;
}
static const struct file_operations bm_entry_operations = {
.read = bm_entry_read,
.write = bm_entry_write,
.llseek = default_llseek,
};
/* /register */
static ssize_t bm_register_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
Node *e;
struct inode *inode;
struct super_block *sb = file_inode(file)->i_sb;
struct dentry *root = sb->s_root, *dentry;
struct binfmt_misc *misc;
int err = 0;
struct file *f = NULL;
e = create_entry(buffer, count);
if (IS_ERR(e))
return PTR_ERR(e);
if (e->flags & MISC_FMT_OPEN_FILE) {
const struct cred *old_cred;
/*
* Now that we support unprivileged binfmt_misc mounts make
* sure we use the credentials that the register @file was
* opened with to also open the interpreter. Before that this
* didn't matter much as only a privileged process could open
* the register file.
*/
old_cred = override_creds(file->f_cred);
f = open_exec(e->interpreter);
revert_creds(old_cred);
if (IS_ERR(f)) {
pr_notice("register: failed to install interpreter file %s\n",
e->interpreter);
kfree(e);
return PTR_ERR(f);
}
e->interp_file = f;
}
inode_lock(d_inode(root));
dentry = lookup_one_len(e->name, root, strlen(e->name));
err = PTR_ERR(dentry);
if (IS_ERR(dentry))
goto out;
err = -EEXIST;
if (d_really_is_positive(dentry))
goto out2;
inode = bm_get_inode(sb, S_IFREG | 0644);
err = -ENOMEM;
if (!inode)
goto out2;
refcount_set(&e->users, 1);
e->dentry = dget(dentry);
inode->i_private = e;
inode->i_fop = &bm_entry_operations;
d_instantiate(dentry, inode);
misc = i_binfmt_misc(inode);
write_lock(&misc->entries_lock);
list_add(&e->list, &misc->entries);
write_unlock(&misc->entries_lock);
err = 0;
out2:
dput(dentry);
out:
inode_unlock(d_inode(root));
if (err) {
if (f)
filp_close(f, NULL);
kfree(e);
return err;
}
return count;
}
static const struct file_operations bm_register_operations = {
.write = bm_register_write,
.llseek = noop_llseek,
};
/* /status */
static ssize_t
bm_status_read(struct file *file, char __user *buf, size_t nbytes, loff_t *ppos)
{
struct binfmt_misc *misc;
char *s;
misc = i_binfmt_misc(file_inode(file));
s = misc->enabled ? "enabled\n" : "disabled\n";
return simple_read_from_buffer(buf, nbytes, ppos, s, strlen(s));
}
static ssize_t bm_status_write(struct file *file, const char __user *buffer,
size_t count, loff_t *ppos)
{
struct binfmt_misc *misc;
int res = parse_command(buffer, count);
Node *e, *next;
struct inode *inode;
misc = i_binfmt_misc(file_inode(file));
switch (res) {
case 1:
/* Disable all handlers. */
misc->enabled = false;
break;
case 2:
/* Enable all handlers. */
misc->enabled = true;
break;
case 3:
/* Delete all handlers. */
inode = d_inode(file_inode(file)->i_sb->s_root);
inode_lock(inode);
/*
* In order to add new element or remove elements from the list
* via bm_{entry,register,status}_write() inode_lock() on the
* root inode must be held.
* The lock is exclusive ensuring that the list can't be
* modified. Only load_misc_binary() can access but does so
* read-only. So we only need to take the write lock when we
* actually remove the entry from the list.
*/
list_for_each_entry_safe(e, next, &misc->entries, list)
remove_binfmt_handler(misc, e);
inode_unlock(inode);
break;
default:
return res;
}
return count;
}
static const struct file_operations bm_status_operations = {
.read = bm_status_read,
.write = bm_status_write,
.llseek = default_llseek,
};
/* Superblock handling */
static void bm_put_super(struct super_block *sb)
{
struct user_namespace *user_ns = sb->s_fs_info;
sb->s_fs_info = NULL;
put_user_ns(user_ns);
}
static const struct super_operations s_ops = {
.statfs = simple_statfs,
.evict_inode = bm_evict_inode,
.put_super = bm_put_super,
};
static int bm_fill_super(struct super_block *sb, struct fs_context *fc)
{
int err;
struct user_namespace *user_ns = sb->s_user_ns;
struct binfmt_misc *misc;
static const struct tree_descr bm_files[] = {
[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
[3] = {"register", &bm_register_operations, S_IWUSR},
/* last one */ {""}
};
if (WARN_ON(user_ns != current_user_ns()))
return -EINVAL;
/*
* Lazily allocate a new binfmt_misc instance for this namespace, i.e.
* do it here during the first mount of binfmt_misc. We don't need to
* waste memory for every user namespace allocation. It's likely much
* more common to not mount a separate binfmt_misc instance than it is
* to mount one.
*
* While multiple superblocks can exist they are keyed by userns in
* s_fs_info for binfmt_misc. Hence, the vfs guarantees that
* bm_fill_super() is called exactly once whenever a binfmt_misc
* superblock for a userns is created. This in turn lets us conclude
* that when a binfmt_misc superblock is created for the first time for
* a userns there's no one racing us. Therefore we don't need any
* barriers when we dereference binfmt_misc.
*/
misc = user_ns->binfmt_misc;
if (!misc) {
/*
* If it turns out that most user namespaces actually want to
* register their own binary type handler and therefore all
* create their own separate binfm_misc mounts we should
* consider turning this into a kmem cache.
*/
misc = kzalloc(sizeof(struct binfmt_misc), GFP_KERNEL);
if (!misc)
return -ENOMEM;
INIT_LIST_HEAD(&misc->entries);
rwlock_init(&misc->entries_lock);
/* Pairs with smp_load_acquire() in load_binfmt_misc(). */
smp_store_release(&user_ns->binfmt_misc, misc);
}
/*
* When the binfmt_misc superblock for this userns is shutdown
* ->enabled might have been set to false and we don't reinitialize
* ->enabled again in put_super() as someone might already be mounting
* binfmt_misc again. It also would be pointless since by the time
* ->put_super() is called we know that the binary type list for this
* bintfmt_misc mount is empty making load_misc_binary() return
* -ENOEXEC independent of whether ->enabled is true. Instead, if
* someone mounts binfmt_misc for the first time or again we simply
* reset ->enabled to true.
*/
misc->enabled = true;
err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
if (!err)
sb->s_op = &s_ops;
return err;
}
static void bm_free(struct fs_context *fc)
{
if (fc->s_fs_info)
put_user_ns(fc->s_fs_info);
}
static int bm_get_tree(struct fs_context *fc)
{
return get_tree_keyed(fc, bm_fill_super, get_user_ns(fc->user_ns));
}
static const struct fs_context_operations bm_context_ops = {
.free = bm_free,
.get_tree = bm_get_tree,
};
static int bm_init_fs_context(struct fs_context *fc)
{
fc->ops = &bm_context_ops;
return 0;
}
static struct linux_binfmt misc_format = {
.module = THIS_MODULE,
.load_binary = load_misc_binary,
};
static struct file_system_type bm_fs_type = {
.owner = THIS_MODULE,
.name = "binfmt_misc",
.init_fs_context = bm_init_fs_context,
.fs_flags = FS_USERNS_MOUNT,
.kill_sb = kill_litter_super,
};
MODULE_ALIAS_FS("binfmt_misc");
static int __init init_misc_binfmt(void)
{
int err = register_filesystem(&bm_fs_type);
if (!err)
insert_binfmt(&misc_format);
return err;
}
static void __exit exit_misc_binfmt(void)
{
unregister_binfmt(&misc_format);
unregister_filesystem(&bm_fs_type);
}
core_initcall(init_misc_binfmt);
module_exit(exit_misc_binfmt);
MODULE_LICENSE("GPL");