security/ccsecurity/realpath.c

/*
 * security/ccsecurity/realpath.c
 *
 * Copyright (C) 2005-2009  NTT DATA CORPORATION
 *
 * Version: 1.7.0-pre   2009/08/08
 *
 * This file is applicable to both 2.4.30 and 2.6.11 and later.
 * See README.ccs for ChangeLog.
 *
 */

#include <linux/string.h>
#include <linux/mm.h>
#include <linux/utime.h>
#include <linux/file.h>
#include <linux/smp_lock.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <asm/uaccess.h>
#include <asm/atomic.h>
#include <linux/version.h>
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 0)
#include <linux/namei.h>
#include <linux/mount.h>
static const int ccs_lookup_flags = LOOKUP_FOLLOW;
#else
static const int ccs_lookup_flags = LOOKUP_FOLLOW | LOOKUP_POSITIVE;
#endif
#include <net/sock.h>
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 0)
#include <linux/kthread.h>
#endif
#include <linux/proc_fs.h>
#include "internal.h"

static int ccs_kern_path(const char *pathname, int flags, struct path *path)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 28)
        if (!pathname || kern_path(pathname, flags, path))
                return -ENOENT;
#else
        struct nameidata nd;
        if (!pathname || path_lookup(pathname, flags, &nd))
                return -ENOENT;
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 25)
        *path = nd.path;
#else
        path->dentry = nd.dentry;
        path->mnt = nd.mnt;
#endif
#endif
        return 0;
}

/**
 * ccs_get_absolute_path - Get the path of a dentry but ignores chroot'ed root.
 *
 * @path:   Pointer to "struct path".
 * @buffer: Pointer to buffer to return value in.
 * @buflen: Sizeof @buffer.
 *
 * Returns the buffer on success, an error code otherwise.
 *
 * Caller holds the dcache_lock and vfsmount_lock.
 * Based on __d_path() in fs/dcache.c
 *
 * If dentry is a directory, trailing '/' is appended.
 * /proc/pid is represented as /proc/self if pid is current.
 */
static char *ccs_get_absolute_path(struct path *path, char * const buffer,
                                   const int buflen)
{
        char *pos = buffer + buflen - 1;
        struct dentry *dentry = path->dentry;
        struct vfsmount *vfsmnt = path->mnt;
        bool is_dir = (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode));
        const char *name;
        int len;

        if (buflen < 256)
                goto out;
        
        *pos = '\0';
        for (;;) {
                struct dentry *parent;
                if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
                        if (vfsmnt->mnt_parent == vfsmnt)
                                break;
                        dentry = vfsmnt->mnt_mountpoint;
                        vfsmnt = vfsmnt->mnt_parent;
                        continue;
                }
                if (is_dir) {
                        is_dir = false;
                        *--pos = '/';
                }
                parent = dentry->d_parent;
                name = dentry->d_name.name;
                len = dentry->d_name.len;
                if (IS_ROOT(parent) && *name > '0' && *name <= '9' &&
                    parent->d_sb &&
                    parent->d_sb->s_magic == PROC_SUPER_MAGIC) {
                        char *ep;
                        const pid_t pid = (pid_t) simple_strtoul(name, &ep,
                                                                 10);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 25)
                        const pid_t tgid = task_tgid_nr_ns(current,
                                                           dentry->d_sb->
                                                           s_fs_info);
                        if (!*ep && pid == tgid && tgid) {
                                name = "self";
                                len = 4;
                        }
#else
                        if (!*ep && pid == sys_getpid()) {
                                name = "self";
                                len = 4;
                        }
#endif
                }
                pos -= len;
                if (pos <= buffer)
                        goto out;
                memmove(pos, name, len);
                *--pos = '/';
                dentry = parent;
        }
        if (*pos == '/')
                pos++;
        len = dentry->d_name.len;
        pos -= len;
        if (pos < buffer)
                goto out;
        memmove(pos, dentry->d_name.name, len);
        return pos;
 out:
        return ERR_PTR(-ENOMEM);
}

#define SOCKFS_MAGIC 0x534F434B

/**
 * ccs_realpath_from_path - Returns realpath(3) of the given pathname but ignores chroot'ed root.
 *
 * @path: Pointer to "struct path".
 *
 * Returns the realpath of the given @path on success, NULL otherwise.
 *
 * This function uses kzalloc(), so caller must kfree() if this function
 * didn't return NULL.
 */
char *ccs_realpath_from_path(struct path *path)
{
        char *buf = NULL;
        char *cp = NULL;
        unsigned int buf_len = PAGE_SIZE / 2;
        struct dentry *dentry = path->dentry;
        if (!dentry)
                return NULL;
 retry:
        buf_len <<= 1;
        kfree(buf);
        buf = kmalloc(buf_len, GFP_KERNEL);
        if (!buf)
                goto done;
        /* Get better name for socket. */
        if (dentry->d_sb && dentry->d_sb->s_magic == SOCKFS_MAGIC) {
                struct inode *inode = dentry->d_inode;
                struct socket *sock = inode ? SOCKET_I(inode) : NULL;
                struct sock *sk = sock ? sock->sk : NULL;
                if (sk) {
                        snprintf(buf, buf_len - 1,
                                 "socket:[family=%u:type=%u:protocol=%u]",
                                 sk->sk_family, sk->sk_type, sk->sk_protocol);
                } else {
                        snprintf(buf, buf_len - 1, "socket:[unknown]");
                }
                cp = ccs_encode(buf);
                goto done;
        }
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 22)
        /* For "socket:[\$]" and "pipe:[\$]". */
        if (dentry->d_op && dentry->d_op->d_dname) {
                cp = dentry->d_op->d_dname(dentry, buf, buf_len - 1);
                if (IS_ERR(cp))
                        goto retry;
                cp = ccs_encode(cp);
                goto done;
        }
#endif
        if (!path->mnt) {
                kfree(buf);
                return NULL;
        }
        path_get(path);
        ccs_realpath_lock();
        cp = ccs_get_absolute_path(path, buf, buf_len - 1);
        ccs_realpath_unlock();
        path_put(path);
        if (IS_ERR(cp))
                goto retry;
        cp = ccs_encode(cp);
 done:
        kfree(buf);
        if (!cp)
                ccs_warn_oom(__func__);
        return cp;
}

/**
 * ccs_symlink_path - Get symlink's pathname.
 *
 * @pathname: The pathname to solve.
 * @name:     Pointer to "struct ccs_path_info".
 *
 * Returns 0 on success, negative value otherwise.
 *
 * This function uses kzalloc(), so caller must kfree() if this function
 * didn't return NULL.
 */
int ccs_symlink_path(const char *pathname, struct ccs_path_info *name)
{
        char *buf;
        struct path path;
        if (ccs_kern_path(pathname, ccs_lookup_flags ^ LOOKUP_FOLLOW, &path))
                return -ENOENT;
        buf = ccs_realpath_from_path(&path);
        path_put(&path);
        if (buf) {
                name->name = buf;
                ccs_fill_path_info(name);
                return 0;
        }
        return -ENOMEM;
}

/**
 * ccs_encode: Encode binary string to ascii string.
 *
 * @str: String in binary format.
 *
 * Returns pointer to @str in ascii format on success, NULL otherwise.
 *
 * This function uses kzalloc(), so caller must kfree() if this function
 * didn't return NULL.
 */
char *ccs_encode(const char *str)
{
        int len = 0;
        const char *p = str;
        char *cp;
        char *cp0;
        if (!p)
                return NULL;
        while (*p) {
                const unsigned char c = *p++;
                if (c == '\\')
                        len += 2;
                else if (c > ' ' && c < 127)
                        len++;
                else
                        len += 4;
        }
        len++;
        /* Reserve space for appending "/". */
        cp = kzalloc(len + 10, GFP_KERNEL);
        if (!cp)
                return NULL;
        cp0 = cp;
        p = str;
        while (*p) {
                const unsigned char c = *p++;
                if (c == '\\') {
                        *cp++ = '\\';
                        *cp++ = '\\';
                } else if (c > ' ' && c < 127) {
                        *cp++ = c;
                } else {
                        *cp++ = '\\';
                        *cp++ = (c >> 6) + '0';
                        *cp++ = ((c >> 3) & 7) + '0';
                        *cp++ = (c & 7) + '0';
                }
        }
        return cp0;
}

/**
 * ccs_get_path - Get dentry/vfsmmount of a pathname.
 *
 * @pathname: The pathname to solve.
 * @path:     Pointer to "struct path".
 *
 * Returns 0 on success, negative value otherwise.
 */
int ccs_get_path(const char *pathname, struct path *path)
{
        return ccs_kern_path(pathname, ccs_lookup_flags, path);
}