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/*
* binfmt_misc.c
*
* Copyright (C) 1997 Richard Günther
*
* binfmt_misc detects binaries via a magic or filename extension and invokes
* a specified wrapper. See Documentation/binfmt_misc.txt 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.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/syscalls.h>
#include <linux/fs.h>
#include <linux/uaccess.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 */
};
static LIST_HEAD(entries);
static int enabled = 1;
enum {Enabled, Magic};
#define MISC_FMT_PRESERVE_ARGV0 (1 << 31)
#define MISC_FMT_OPEN_BINARY (1 << 30)
#define MISC_FMT_CREDENTIALS (1 << 29)
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 */
char *interpreter; /* filename of interpreter */
char *name;
struct dentry *dentry;
} Node;
static DEFINE_RWLOCK(entries_lock);
static struct file_system_type bm_fs_type;
static struct vfsmount *bm_mnt;
static int entry_count;
/*
* 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
/*
* Check if we support the binfmt
* if we do, return the node, else NULL
* locking is done in load_misc_binary
*/
static Node *check_file(struct linux_binprm *bprm)
{
char *p = strrchr(bprm->interp, '.');
struct list_head *l;
/* Walk all the registered handlers. */
list_for_each(l, &entries) {
Node *e = list_entry(l, Node, 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;
}
/*
* the loader itself
*/
static int load_misc_binary(struct linux_binprm *bprm)
{
Node *fmt;
struct file *interp_file = NULL;
char iname[BINPRM_BUF_SIZE];
const char *iname_addr = iname;
int retval;
int fd_binary = -1;
retval = -ENOEXEC;
if (!enabled)
goto ret;
/* to keep locking time low, we copy the interpreter string */
read_lock(&entries_lock);
fmt = check_file(bprm);
if (fmt)
strlcpy(iname, fmt->interpreter, BINPRM_BUF_SIZE);
read_unlock(&entries_lock);
if (!fmt)
goto ret;
/* Need to be able to load the file after exec */
if (bprm->interp_flags & BINPRM_FLAGS_PATH_INACCESSIBLE)
return -ENOENT;
if (!(fmt->flags & MISC_FMT_PRESERVE_ARGV0)) {
retval = remove_arg_zero(bprm);
if (retval)
goto ret;
}
if (fmt->flags & MISC_FMT_OPEN_BINARY) {
/* if the binary should be opened on behalf of the
* interpreter than keep it open and assign descriptor
* to it
*/
fd_binary = get_unused_fd_flags(0);
if (fd_binary < 0) {
retval = fd_binary;
goto ret;
}
fd_install(fd_binary, bprm->file);
/* if the binary is not readable than enforce mm->dumpable=0
regardless of the interpreter's permissions */
would_dump(bprm, bprm->file);
allow_write_access(bprm->file);
bprm->file = NULL;
/* mark the bprm that fd should be passed to interp */
bprm->interp_flags |= BINPRM_FLAGS_EXECFD;
bprm->interp_data = fd_binary;
} else {
allow_write_access(bprm->file);
fput(bprm->file);
bprm->file = NULL;
}
/* make argv[1] be the path to the binary */
retval = copy_strings_kernel(1, &bprm->interp, bprm);
if (retval < 0)
goto error;
bprm->argc++;
/* add the interp as argv[0] */
retval = copy_strings_kernel(1, &iname_addr, bprm);
if (retval < 0)
goto error;
bprm->argc++;
/* Update interp in case binfmt_script needs it. */
retval = bprm_change_interp(iname, bprm);
if (retval < 0)
goto error;
interp_file = open_exec(iname);
retval = PTR_ERR(interp_file);
if (IS_ERR(interp_file))
goto error;
bprm->file = interp_file;
if (fmt->flags & MISC_FMT_CREDENTIALS) {
/*
* No need to call prepare_binprm(), it's already been
* done. bprm->buf is stale, update from interp_file.
*/
memset(bprm->buf, 0, BINPRM_BUF_SIZE);
retval = kernel_read(bprm->file, 0, bprm->buf, BINPRM_BUF_SIZE);
} else
retval = prepare_binprm(bprm);
if (retval < 0)
goto error;
retval = search_binary_handler(bprm);
if (retval < 0)
goto error;
ret:
return retval;
error:
if (fd_binary > 0)
sys_close(fd_binary);
bprm->interp_flags = 0;
bprm->interp_data = 0;
goto ret;
}
/* 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;
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);
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';
e->offset = simple_strtoul(p, &p, 10);
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 + e->offset > BINPRM_BUF_SIZE)
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);
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';
*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;
inode->i_atime = inode->i_mtime = inode->i_ctime =
current_fs_time(inode->i_sb);
}
return inode;
}
static void bm_evict_inode(struct inode *inode)
{
clear_inode(inode);
kfree(inode->i_private);
}
static void kill_node(Node *e)
{
struct dentry *dentry;
write_lock(&entries_lock);
dentry = e->dentry;
if (dentry) {
list_del_init(&e->list);
e->dentry = NULL;
}
write_unlock(&entries_lock);
if (dentry) {
drop_nlink(d_inode(dentry));
d_drop(dentry);
dput(dentry);
simple_release_fs(&bm_mnt, &entry_count);
}
}
/* /<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 dentry *root;
Node *e = file_inode(file)->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. */
root = dget(file->f_path.dentry->d_sb->s_root);
mutex_lock(&d_inode(root)->i_mutex);
kill_node(e);
mutex_unlock(&d_inode(root)->i_mutex);
dput(root);
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 dentry *root, *dentry;
struct super_block *sb = file->f_path.dentry->d_sb;
int err = 0;
e = create_entry(buffer, count);
if (IS_ERR(e))
return PTR_ERR(e);
root = dget(sb->s_root);
mutex_lock(&d_inode(root)->i_mutex);
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;
err = simple_pin_fs(&bm_fs_type, &bm_mnt, &entry_count);
if (err) {
iput(inode);
inode = NULL;
goto out2;
}
e->dentry = dget(dentry);
inode->i_private = e;
inode->i_fop = &bm_entry_operations;
d_instantiate(dentry, inode);
write_lock(&entries_lock);
list_add(&e->list, &entries);
write_unlock(&entries_lock);
err = 0;
out2:
dput(dentry);
out:
mutex_unlock(&d_inode(root)->i_mutex);
dput(root);
if (err) {
kfree(e);
return -EINVAL;
}
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)
{
char *s = 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)
{
int res = parse_command(buffer, count);
struct dentry *root;
switch (res) {
case 1:
/* Disable all handlers. */
enabled = 0;
break;
case 2:
/* Enable all handlers. */
enabled = 1;
break;
case 3:
/* Delete all handlers. */
root = dget(file->f_path.dentry->d_sb->s_root);
mutex_lock(&d_inode(root)->i_mutex);
while (!list_empty(&entries))
kill_node(list_entry(entries.next, Node, list));
mutex_unlock(&d_inode(root)->i_mutex);
dput(root);
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 const struct super_operations s_ops = {
.statfs = simple_statfs,
.evict_inode = bm_evict_inode,
};
static int bm_fill_super(struct super_block *sb, void *data, int silent)
{
int err;
static struct tree_descr bm_files[] = {
[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
[3] = {"register", &bm_register_operations, S_IWUSR},
/* last one */ {""}
};
err = simple_fill_super(sb, BINFMTFS_MAGIC, bm_files);
if (!err)
sb->s_op = &s_ops;
return err;
}
static struct dentry *bm_mount(struct file_system_type *fs_type,
int flags, const char *dev_name, void *data)
{
return mount_single(fs_type, flags, data, bm_fill_super);
}
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",
.mount = bm_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");
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