linux/net/core/scm.c
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   1/* scm.c - Socket level control messages processing.
   2 *
   3 * Author:      Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   4 *              Alignment and value checking mods by Craig Metz
   5 *
   6 *              This program is free software; you can redistribute it and/or
   7 *              modify it under the terms of the GNU General Public License
   8 *              as published by the Free Software Foundation; either version
   9 *              2 of the License, or (at your option) any later version.
  10 */
  11
  12#include <linux/module.h>
  13#include <linux/signal.h>
  14#include <linux/capability.h>
  15#include <linux/errno.h>
  16#include <linux/sched.h>
  17#include <linux/mm.h>
  18#include <linux/kernel.h>
  19#include <linux/stat.h>
  20#include <linux/socket.h>
  21#include <linux/file.h>
  22#include <linux/fcntl.h>
  23#include <linux/net.h>
  24#include <linux/interrupt.h>
  25#include <linux/netdevice.h>
  26#include <linux/security.h>
  27#include <linux/pid.h>
  28#include <linux/nsproxy.h>
  29#include <linux/slab.h>
  30
  31#include <asm/uaccess.h>
  32
  33#include <net/protocol.h>
  34#include <linux/skbuff.h>
  35#include <net/sock.h>
  36#include <net/compat.h>
  37#include <net/scm.h>
  38
  39
  40/*
  41 *      Only allow a user to send credentials, that they could set with
  42 *      setu(g)id.
  43 */
  44
  45static __inline__ int scm_check_creds(struct ucred *creds)
  46{
  47        const struct cred *cred = current_cred();
  48        kuid_t uid = make_kuid(cred->user_ns, creds->uid);
  49        kgid_t gid = make_kgid(cred->user_ns, creds->gid);
  50
  51        if (!uid_valid(uid) || !gid_valid(gid))
  52                return -EINVAL;
  53
  54        if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
  55            ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
  56              uid_eq(uid, cred->suid)) || capable(CAP_SETUID)) &&
  57            ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
  58              gid_eq(gid, cred->sgid)) || capable(CAP_SETGID))) {
  59               return 0;
  60        }
  61        return -EPERM;
  62}
  63
  64static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  65{
  66        int *fdp = (int*)CMSG_DATA(cmsg);
  67        struct scm_fp_list *fpl = *fplp;
  68        struct file **fpp;
  69        int i, num;
  70
  71        num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  72
  73        if (num <= 0)
  74                return 0;
  75
  76        if (num > SCM_MAX_FD)
  77                return -EINVAL;
  78
  79        if (!fpl)
  80        {
  81                fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  82                if (!fpl)
  83                        return -ENOMEM;
  84                *fplp = fpl;
  85                fpl->count = 0;
  86                fpl->max = SCM_MAX_FD;
  87        }
  88        fpp = &fpl->fp[fpl->count];
  89
  90        if (fpl->count + num > fpl->max)
  91                return -EINVAL;
  92
  93        /*
  94         *      Verify the descriptors and increment the usage count.
  95         */
  96
  97        for (i=0; i< num; i++)
  98        {
  99                int fd = fdp[i];
 100                struct file *file;
 101
 102                if (fd < 0 || !(file = fget_raw(fd)))
 103                        return -EBADF;
 104                *fpp++ = file;
 105                fpl->count++;
 106        }
 107        return num;
 108}
 109
 110void __scm_destroy(struct scm_cookie *scm)
 111{
 112        struct scm_fp_list *fpl = scm->fp;
 113        int i;
 114
 115        if (fpl) {
 116                scm->fp = NULL;
 117                for (i=fpl->count-1; i>=0; i--)
 118                        fput(fpl->fp[i]);
 119                kfree(fpl);
 120        }
 121}
 122EXPORT_SYMBOL(__scm_destroy);
 123
 124int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 125{
 126        struct cmsghdr *cmsg;
 127        int err;
 128
 129        for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 130        {
 131                err = -EINVAL;
 132
 133                /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 134                /* The first check was omitted in <= 2.2.5. The reasoning was
 135                   that parser checks cmsg_len in any case, so that
 136                   additional check would be work duplication.
 137                   But if cmsg_level is not SOL_SOCKET, we do not check
 138                   for too short ancillary data object at all! Oops.
 139                   OK, let's add it...
 140                 */
 141                if (!CMSG_OK(msg, cmsg))
 142                        goto error;
 143
 144                if (cmsg->cmsg_level != SOL_SOCKET)
 145                        continue;
 146
 147                switch (cmsg->cmsg_type)
 148                {
 149                case SCM_RIGHTS:
 150                        if (!sock->ops || sock->ops->family != PF_UNIX)
 151                                goto error;
 152                        err=scm_fp_copy(cmsg, &p->fp);
 153                        if (err<0)
 154                                goto error;
 155                        break;
 156                case SCM_CREDENTIALS:
 157                {
 158                        struct ucred creds;
 159                        kuid_t uid;
 160                        kgid_t gid;
 161                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 162                                goto error;
 163                        memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 164                        err = scm_check_creds(&creds);
 165                        if (err)
 166                                goto error;
 167
 168                        p->creds.pid = creds.pid;
 169                        if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 170                                struct pid *pid;
 171                                err = -ESRCH;
 172                                pid = find_get_pid(creds.pid);
 173                                if (!pid)
 174                                        goto error;
 175                                put_pid(p->pid);
 176                                p->pid = pid;
 177                        }
 178
 179                        err = -EINVAL;
 180                        uid = make_kuid(current_user_ns(), creds.uid);
 181                        gid = make_kgid(current_user_ns(), creds.gid);
 182                        if (!uid_valid(uid) || !gid_valid(gid))
 183                                goto error;
 184
 185                        p->creds.uid = uid;
 186                        p->creds.gid = gid;
 187
 188                        if (!p->cred ||
 189                            !uid_eq(p->cred->euid, uid) ||
 190                            !gid_eq(p->cred->egid, gid)) {
 191                                struct cred *cred;
 192                                err = -ENOMEM;
 193                                cred = prepare_creds();
 194                                if (!cred)
 195                                        goto error;
 196
 197                                cred->uid = cred->euid = uid;
 198                                cred->gid = cred->egid = gid;
 199                                if (p->cred)
 200                                        put_cred(p->cred);
 201                                p->cred = cred;
 202                        }
 203                        break;
 204                }
 205                default:
 206                        goto error;
 207                }
 208        }
 209
 210        if (p->fp && !p->fp->count)
 211        {
 212                kfree(p->fp);
 213                p->fp = NULL;
 214        }
 215        return 0;
 216
 217error:
 218        scm_destroy(p);
 219        return err;
 220}
 221EXPORT_SYMBOL(__scm_send);
 222
 223int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 224{
 225        struct cmsghdr __user *cm
 226                = (__force struct cmsghdr __user *)msg->msg_control;
 227        struct cmsghdr cmhdr;
 228        int cmlen = CMSG_LEN(len);
 229        int err;
 230
 231        if (MSG_CMSG_COMPAT & msg->msg_flags)
 232                return put_cmsg_compat(msg, level, type, len, data);
 233
 234        if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 235                msg->msg_flags |= MSG_CTRUNC;
 236                return 0; /* XXX: return error? check spec. */
 237        }
 238        if (msg->msg_controllen < cmlen) {
 239                msg->msg_flags |= MSG_CTRUNC;
 240                cmlen = msg->msg_controllen;
 241        }
 242        cmhdr.cmsg_level = level;
 243        cmhdr.cmsg_type = type;
 244        cmhdr.cmsg_len = cmlen;
 245
 246        err = -EFAULT;
 247        if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 248                goto out;
 249        if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 250                goto out;
 251        cmlen = CMSG_SPACE(len);
 252        if (msg->msg_controllen < cmlen)
 253                cmlen = msg->msg_controllen;
 254        msg->msg_control += cmlen;
 255        msg->msg_controllen -= cmlen;
 256        err = 0;
 257out:
 258        return err;
 259}
 260EXPORT_SYMBOL(put_cmsg);
 261
 262void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 263{
 264        struct cmsghdr __user *cm
 265                = (__force struct cmsghdr __user*)msg->msg_control;
 266
 267        int fdmax = 0;
 268        int fdnum = scm->fp->count;
 269        struct file **fp = scm->fp->fp;
 270        int __user *cmfptr;
 271        int err = 0, i;
 272
 273        if (MSG_CMSG_COMPAT & msg->msg_flags) {
 274                scm_detach_fds_compat(msg, scm);
 275                return;
 276        }
 277
 278        if (msg->msg_controllen > sizeof(struct cmsghdr))
 279                fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 280                         / sizeof(int));
 281
 282        if (fdnum < fdmax)
 283                fdmax = fdnum;
 284
 285        for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 286             i++, cmfptr++)
 287        {
 288                struct socket *sock;
 289                int new_fd;
 290                err = security_file_receive(fp[i]);
 291                if (err)
 292                        break;
 293                err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 294                                          ? O_CLOEXEC : 0);
 295                if (err < 0)
 296                        break;
 297                new_fd = err;
 298                err = put_user(new_fd, cmfptr);
 299                if (err) {
 300                        put_unused_fd(new_fd);
 301                        break;
 302                }
 303                /* Bump the usage count and install the file. */
 304                sock = sock_from_file(fp[i], &err);
 305                if (sock)
 306                        sock_update_netprioidx(sock->sk, current);
 307                fd_install(new_fd, get_file(fp[i]));
 308        }
 309
 310        if (i > 0)
 311        {
 312                int cmlen = CMSG_LEN(i*sizeof(int));
 313                err = put_user(SOL_SOCKET, &cm->cmsg_level);
 314                if (!err)
 315                        err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 316                if (!err)
 317                        err = put_user(cmlen, &cm->cmsg_len);
 318                if (!err) {
 319                        cmlen = CMSG_SPACE(i*sizeof(int));
 320                        msg->msg_control += cmlen;
 321                        msg->msg_controllen -= cmlen;
 322                }
 323        }
 324        if (i < fdnum || (fdnum && fdmax <= 0))
 325                msg->msg_flags |= MSG_CTRUNC;
 326
 327        /*
 328         * All of the files that fit in the message have had their
 329         * usage counts incremented, so we just free the list.
 330         */
 331        __scm_destroy(scm);
 332}
 333EXPORT_SYMBOL(scm_detach_fds);
 334
 335struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 336{
 337        struct scm_fp_list *new_fpl;
 338        int i;
 339
 340        if (!fpl)
 341                return NULL;
 342
 343        new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 344                          GFP_KERNEL);
 345        if (new_fpl) {
 346                for (i = 0; i < fpl->count; i++)
 347                        get_file(fpl->fp[i]);
 348                new_fpl->max = new_fpl->count;
 349        }
 350        return new_fpl;
 351}
 352EXPORT_SYMBOL(scm_fp_dup);
 353
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