security/ccsecurity/realpath.c

/*
 * security/ccsecurity/realpath.c
 *
 * Copyright (C) 2005-2011  NTT DATA CORPORATION
 *
 * Version: 1.8.0+   2011/01/11
 */

#include "internal.h"
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 0)
#define ccs_lookup_flags LOOKUP_FOLLOW
#else
#define ccs_lookup_flags (LOOKUP_FOLLOW | LOOKUP_POSITIVE)
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 5, 0)
#define s_fs_info u.generic_sbp
#endif

#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 5, 0)

/**
 * SOCKET_I - Get "struct socket".
 *
 * @inode: Pointer to "struct inode".
 *
 * Returns pointer to "struct socket".
 *
 * This is for compatibility with older kernels.
 */
static inline struct socket *SOCKET_I(struct inode *inode)
{
        return inode->i_sock ? &inode->u.socket_i : NULL;
}

#endif

#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 37)

/**
 * ccs_realpath_lock - Take locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_lock(void)
{
        /* dcache_lock is locked by __d_path(). */
        /* vfsmount_lock is locked by __d_path(). */
}

/**
 * ccs_realpath_unlock - Release locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_unlock(void)
{
        /* vfsmount_lock is unlocked by __d_path(). */
        /* dcache_lock is unlocked by __d_path(). */
}

#elif LINUX_VERSION_CODE == KERNEL_VERSION(2, 6, 36)

/**
 * ccs_realpath_lock - Take locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_lock(void)
{
        spin_lock(&dcache_lock);
        /* vfsmount_lock is locked by __d_path(). */
}

/**
 * ccs_realpath_unlock - Release locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_unlock(void)
{
        /* vfsmount_lock is unlocked by __d_path(). */
        spin_unlock(&dcache_lock);
}

#elif defined(D_PATH_DISCONNECT) && !defined(CONFIG_SUSE_KERNEL)

/**
 * ccs_realpath_lock - Take locks for __d_path().
 *
 * Returns nothing.
 *
 * Original unambiguous-__d_path.diff in patches.apparmor.tar.bz2 inversed the
 * order of holding dcache_lock and vfsmount_lock. That patch was applied on
 * (at least) SUSE 11.1 and Ubuntu 8.10 and Ubuntu 9.04 kernels.
 *
 * However, that patch was updated to use original order and the updated patch
 * is applied to (as far as I know) only SUSE kernels.
 *
 * Therefore, I need to use original order for SUSE 11.1 kernels and inversed
 * order for other kernels. I detect it by checking D_PATH_DISCONNECT and
 * CONFIG_SUSE_KERNEL. I don't know whether other distributions are using the
 * updated patch or not. If you got deadlock, check fs/dcache.c for locking
 * order, and add " && 0" to this "#elif " block if fs/dcache.c uses original
 * order.
 */
static inline void ccs_realpath_lock(void)
{
        spin_lock(ccsecurity_exports.vfsmount_lock);
        spin_lock(&dcache_lock);
}

/**
 * ccs_realpath_unlock - Release locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_unlock(void)
{
        spin_unlock(&dcache_lock);
        spin_unlock(ccsecurity_exports.vfsmount_lock);
}

#elif LINUX_VERSION_CODE >= KERNEL_VERSION(2, 5, 0)

/**
 * ccs_realpath_lock - Take locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_lock(void)
{
        spin_lock(&dcache_lock);
        spin_lock(ccsecurity_exports.vfsmount_lock);
}

/**
 * ccs_realpath_unlock - Release locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_unlock(void)
{
        spin_unlock(ccsecurity_exports.vfsmount_lock);
        spin_unlock(&dcache_lock);
}

#else

/**
 * ccs_realpath_lock - Take locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_lock(void)
{
        spin_lock(&dcache_lock);
}

/**
 * ccs_realpath_unlock - Release locks for __d_path().
 *
 * Returns nothing.
 */
static inline void ccs_realpath_unlock(void)
{
        spin_unlock(&dcache_lock);
}

#endif

/**
 * ccs_kern_path - Wrapper for kern_path().
 *
 * @pathname: Pathname to resolve. Maybe NULL.
 * @flags:    Lookup flags.
 * @path:     Pointer to "struct path".
 *
 * Returns 0 on success, negative value otherwise.
 */
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.
 */
static char *ccs_get_absolute_path(struct path *path, char * const buffer,
                                   const int buflen)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 36)
        char *pos = ERR_PTR(-ENOMEM);
        if (buflen >= 256) {
                struct path root = { };
                pos = ccsecurity_exports.__d_path(path, &root, buffer,
                                                  buflen - 1);
                if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
                        struct inode *inode = path->dentry->d_inode;
                        if (inode && S_ISDIR(inode->i_mode)) {
                                buffer[buflen - 2] = '/';
                                buffer[buflen - 1] = '\0';
                        }
                }
        }
        return pos;
#else
        char *pos = buffer + buflen - 1;
        struct dentry *dentry = path->dentry;
        struct vfsmount *vfsmnt = path->mnt;
        const char *name;
        int len;

        if (buflen < 256)
                goto out;

        *pos = '\0';
        if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode))
                *--pos = '/';
        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;
                }
                parent = dentry->d_parent;
                name = dentry->d_name.name;
                len = dentry->d_name.len;
                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);
#endif
}

/**
 * ccs_get_dentry_path - Get the path of a dentry.
 *
 * @dentry: Pointer to "struct dentry".
 * @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.
 * Based on dentry_path() in fs/dcache.c
 *
 * If dentry is a directory, trailing '/' is appended.
 */
static char *ccs_get_dentry_path(struct dentry *dentry, char * const buffer,
                                 const int buflen)
{
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 38)
        char *pos = ERR_PTR(-ENOMEM);
        if (buflen >= 256) {
                /* rename_lock is locked/unlocked by dentry_path_raw(). */
                pos = dentry_path_raw(dentry, buffer, buflen - 1);
                if (!IS_ERR(pos) && *pos == '/' && pos[1]) {
                        struct inode *inode = dentry->d_inode;
                        if (inode && S_ISDIR(inode->i_mode)) {
                                buffer[buflen - 2] = '/';
                                buffer[buflen - 1] = '\0';
                        }
                }
        }
        return pos;
#else
        char *pos = buffer + buflen - 1;
        if (buflen < 256)
                goto out;
        *pos = '\0';
        if (dentry->d_inode && S_ISDIR(dentry->d_inode->i_mode))
                *--pos = '/';
        while (!IS_ROOT(dentry)) {
                struct dentry *parent = dentry->d_parent;
                const char *name = dentry->d_name.name;
                const int len = dentry->d_name.len;
                pos -= len;
                if (pos <= buffer)
                        goto out;
                memmove(pos, name, len);
                *--pos = '/';
                dentry = parent;
        }
        return pos;
out:
        return ERR_PTR(-ENOMEM);
#endif
}

/**
 * ccs_get_local_path - Get the path of a dentry.
 *
 * @dentry: Pointer to "struct dentry".
 * @buffer: Pointer to buffer to return value in.
 * @buflen: Sizeof @buffer.
 *
 * Returns the buffer on success, an error code otherwise.
 */
static char *ccs_get_local_path(struct dentry *dentry, char * const buffer,
                                const int buflen)
{
        char *pos;
        struct super_block *sb = dentry->d_sb;
#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 38)
        spin_lock(&dcache_lock);
#endif
        pos = ccs_get_dentry_path(dentry, buffer, buflen);
#if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 38)
        spin_unlock(&dcache_lock);
#endif
        if (IS_ERR(pos))
                return pos;
        /* Convert from $PID to self if $PID is current thread. */
        if (sb->s_magic == PROC_SUPER_MAGIC && *pos == '/') {
                char *ep;
                const pid_t pid = (pid_t) simple_strtoul(pos + 1, &ep, 10);
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 25)
                if (*ep == '/' && pid && pid ==
                    task_tgid_nr_ns(current, sb->s_fs_info)) {
                        pos = ep - 5;
                        if (pos < buffer)
                                goto out;
                        memmove(pos, "/self", 5);
                }
#else
                if (*ep == '/' && pid == ccs_sys_getpid()) {
                        pos = ep - 5;
                        if (pos < buffer)
                                goto out;
                        memmove(pos, "/self", 5);
                }
#endif
                goto prepend_filesystem_name;
        }
        /* Use filesystem name for unnamed devices. */
        if (!MAJOR(sb->s_dev))
                goto prepend_filesystem_name;
        {
                struct inode *inode = sb->s_root->d_inode;
                /*
                 * Use filesystem name if filesystems does not support rename()
                 * operation.
                 */
                if (inode->i_op && !inode->i_op->rename)
                        goto prepend_filesystem_name;
        }
        /* Prepend device name. */
        {
                char name[64];
                int name_len;
                const dev_t dev = sb->s_dev;
                name[sizeof(name) - 1] = '\0';
                snprintf(name, sizeof(name) - 1, "dev(%u,%u):", MAJOR(dev),
                         MINOR(dev));
                name_len = strlen(name);
                pos -= name_len;
                if (pos < buffer)
                        goto out;
                memmove(pos, name, name_len);
                return pos;
        }
        /* Prepend filesystem name. */
prepend_filesystem_name:
        {
                const char *name = sb->s_type->name;
                const int name_len = strlen(name);
                pos -= name_len + 1;
                if (pos < buffer)
                        goto out;
                memmove(pos, name, name_len);
                pos[name_len] = ':';
        }
        return pos;
out:
        return ERR_PTR(-ENOMEM);
}

/**
 * ccs_get_socket_name - Get the name of a socket.
 *
 * @path:   Pointer to "struct path".
 * @buffer: Pointer to buffer to return value in.
 * @buflen: Sizeof @buffer.
 *
 * Returns the buffer.
 */
static char *ccs_get_socket_name(struct path *path, char * const buffer,
                                 const int buflen)
{
        struct inode *inode = path->dentry->d_inode;
        struct socket *sock = inode ? SOCKET_I(inode) : NULL;
        struct sock *sk = sock ? sock->sk : NULL;
        if (sk) {
                snprintf(buffer, buflen, "socket:[family=%u:type=%u:"
                         "protocol=%u]", sk->sk_family, sk->sk_type,
                         sk->sk_protocol);
        } else {
                snprintf(buffer, buflen, "socket:[unknown]");
        }
        return buffer;
}

#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 *name = NULL;
        unsigned int buf_len = PAGE_SIZE / 2;
        struct dentry *dentry = path->dentry;
        struct super_block *sb;
        if (!dentry)
                return NULL;
        sb = dentry->d_sb;
        while (1) {
                char *pos;
                struct inode *inode;
                buf_len <<= 1;
                kfree(buf);
                buf = kmalloc(buf_len, CCS_GFP_FLAGS);
                if (!buf)
                        break;
                /* To make sure that pos is '\0' terminated. */
                buf[buf_len - 1] = '\0';
                /* Get better name for socket. */
                if (sb->s_magic == SOCKFS_MAGIC) {
                        pos = ccs_get_socket_name(path, buf, buf_len - 1);
                        goto encode;
                }
#if LINUX_VERSION_CODE >= KERNEL_VERSION(2, 6, 22)
                /* For "pipe:[\$]". */
                if (dentry->d_op && dentry->d_op->d_dname) {
                        pos = dentry->d_op->d_dname(dentry, buf, buf_len - 1);
                        goto encode;
                }
#endif
                inode = sb->s_root->d_inode;
                /*
                 * Get local name for filesystems without rename() operation
                 * or dentry without vfsmount.
                 */
                if (!path->mnt || (inode->i_op && !inode->i_op->rename)) {
                        pos = ccs_get_local_path(path->dentry, buf,
                                                 buf_len - 1);
                        goto encode;
                }
                /* Get absolute name for the rest. */
                ccs_realpath_lock();
                pos = ccs_get_absolute_path(path, buf, buf_len - 1);
                ccs_realpath_unlock();
encode:
                if (IS_ERR(pos))
                        continue;
                name = ccs_encode(pos);
                break;
        }
        kfree(buf);
        if (!name)
                ccs_warn_oom(__func__);
        return name;
}

/**
 * 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_encode2 - Encode binary string to ascii string.
 *
 * @str:     String in binary format.
 * @str_len: Size of @str in byte.
 *
 * 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_encode2(const char *str, int str_len)
{
        int i;
        int len = 0;
        const char *p = str;
        char *cp;
        char *cp0;
        if (!p)
                return NULL;
        for (i = 0; i < str_len; i++) {
                const unsigned char c = p[i];
                if (c == '\\')
                        len += 2;
                else if (c > ' ' && c < 127)
                        len++;
                else
                        len += 4;
        }
        len++;
        /* Reserve space for appending "/". */
        cp = kzalloc(len + 10, CCS_GFP_FLAGS);
        if (!cp)
                return NULL;
        cp0 = cp;
        p = str;
        for (i = 0; i < str_len; i++) {
                const unsigned char c = p[i];
                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_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)
{
        return str ? ccs_encode2(str, strlen(str)) : NULL;
}

/**
 * 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);
}