binfmt_misc.c

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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. This should obsolete binfmt_java, binfmt_em86 and
 *  binfmt_mz.
 *
 *  1997-04-25 first version
 *  [...]
 *  1997-05-19 cleanup
 *  1997-06-26 hpa: pass the real filename rather than argv[0]
 *  1997-06-30 minor cleanup
 *  1997-08-09 removed extension stripping, locking cleanup
 *  2001-02-28 AV: rewritten into something that resembles C. Original didn't.
 */

#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/file.h>
#include <linux/pagemap.h>
#include <linux/namei.h>
#include <linux/mount.h>
#include <linux/syscalls.h>
#include <linux/fs.h>

#include <asm/uaccess.h>

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;

/* 
 * 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;

    list_for_each(l, &entries) {
        Node *e = list_entry(l, Node, list);
        char *s;
        int j;

        if (!test_bit(Enabled, &e->flags))
            continue;

        if (!test_bit(Magic, &e->flags)) {
            if (p && !strcmp(e->magic, p + 1))
                return e;
            continue;
        }

        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, struct pt_regs *regs)
{
    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;

    retval = -ENOEXEC;
    if (bprm->recursion_depth > BINPRM_MAX_RECURSION)
        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;

    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();
        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 ++;

    bprm->interp = iname;   /* for binfmt_script */

    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;

    bprm->recursion_depth++;

    retval = search_binary_handler (bprm, regs);
    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;
        }
    }
    return s;
}

static int unquote(char *from)
{
    char c = 0, *s = from, *p = from;

    while ((c = *s++) != '\0') {
        if (c == '\\' && *s == 'x') {
            s++;
            c = toupper(*s++);
            *p = (c - (isdigit(c) ? '0' : 'A' - 10)) << 4;
            c = toupper(*s++);
            *p++ |= c - (isdigit(c) ? '0' : 'A' - 10);
            continue;
        }
        *p++ = c;
    }
    return p - from;
}

static char * check_special_flags (char * sfs, Node * e)
{
    char * p = sfs;
    int cont = 1;

    /* special flags */
    while (cont) {
        switch (*p) {
            case 'P':
                p++;
                e->flags |= MISC_FMT_PRESERVE_ARGV0;
                break;
            case 'O':
                p++;
                e->flags |= MISC_FMT_OPEN_BINARY;
                break;
            case 'C':
                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;

    /* some sanity checks */
    err = -EINVAL;
    if ((count < 11) || (count > 256))
        goto out;

    err = -ENOMEM;
    memsize = sizeof(Node) + count + 8;
    e = kmalloc(memsize, GFP_USER);
    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 */

    memset(buf+count, del, 8);

    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;
    switch (*p++) {
        case 'E': e->flags = 1<<Enabled; break;
        case 'M': e->flags = (1<<Enabled) | (1<<Magic); break;
        default: goto Einval;
    }
    if (*p++ != del)
        goto Einval;
    if (test_bit(Magic, &e->flags)) {
        char *s = strchr(p, del);
        if (!s)
            goto Einval;
        *s++ = '\0';
        e->offset = simple_strtoul(p, &p, 10);
        if (*p++)
            goto Einval;
        e->magic = p;
        p = scanarg(p, del);
        if (!p)
            goto Einval;
        p[-1] = '\0';
        if (!e->magic[0])
            goto Einval;
        e->mask = p;
        p = scanarg(p, del);
        if (!p)
            goto Einval;
        p[-1] = '\0';
        if (!e->mask[0])
            e->mask = NULL;
        e->size = unquote(e->magic);
        if (e->mask && unquote(e->mask) != e->size)
            goto Einval;
        if (e->size + e->offset > BINPRM_BUF_SIZE)
            goto Einval;
    } else {
        p = strchr(p, del);
        if (!p)
            goto Einval;
        *p++ = '\0';
        e->magic = p;
        p = strchr(p, del);
        if (!p)
            goto Einval;
        *p++ = '\0';
        if (!e->magic[0] || strchr(e->magic, '/'))
            goto Einval;
        p = strchr(p, del);
        if (!p)
            goto Einval;
        *p++ = '\0';
    }
    e->interpreter = p;
    p = strchr(p, del);
    if (!p)
        goto Einval;
    *p++ = '\0';
    if (!e->interpreter[0])
        goto Einval;


    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)
        return 0;
    if (count > 3)
        return -EINVAL;
    if (copy_from_user(s, buffer, count))
        return -EFAULT;
    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;
    char *status = "disabled";
    const char * flags = "flags: ";

    if (test_bit(Enabled, &e->flags))
        status = "enabled";

    if (!VERBOSE_STATUS) {
        sprintf(page, "%s\n", status);
        return;
    }

    sprintf(page, "%s\ninterpreter %s\n", status, e->interpreter);
    dp = page + strlen(page);

    /* print the special flags */
    sprintf (dp, "%s", flags);
    dp += strlen (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 {
        int i;

        sprintf(dp, "offset %i\nmagic ", e->offset);
        dp = page + strlen(page);
        for (i = 0; i < e->size; i++) {
            sprintf(dp, "%02x", 0xff & (int) (e->magic[i]));
            dp += 2;
        }
        if (e->mask) {
            sprintf(dp, "\nmask ");
            dp += 6;
            for (i = 0; i < e->size; i++) {
                sprintf(dp, "%02x", 0xff & (int) (e->mask[i]));
                dp += 2;
            }
        }
        *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(dentry->d_inode);
        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->f_path.dentry->d_inode->i_private;
    ssize_t res;
    char *page;

    if (!(page = (char*) __get_free_page(GFP_KERNEL)))
        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->f_path.dentry->d_inode->i_private;
    int res = parse_command(buffer, count);

    switch (res) {
        case 1: clear_bit(Enabled, &e->flags);
            break;
        case 2: set_bit(Enabled, &e->flags);
            break;
        case 3: root = dget(file->f_path.dentry->d_sb->s_root);
            mutex_lock(&root->d_inode->i_mutex);

            kill_node(e);

            mutex_unlock(&root->d_inode->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(&root->d_inode->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 (dentry->d_inode)
        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(&root->d_inode->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: enabled = 0; break;
        case 2: enabled = 1; break;
        case 3: root = dget(file->f_path.dentry->d_sb->s_root);
            mutex_lock(&root->d_inode->i_mutex);

            while (!list_empty(&entries))
                kill_node(list_entry(entries.next, Node, list));

            mutex_unlock(&root->d_inode->i_mutex);
            dput(root);
        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)
{
    static struct tree_descr bm_files[] = {
        [2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
        [3] = {"register", &bm_register_operations, S_IWUSR},
        /* last one */ {""}
    };
    int 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,
};

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");