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
  49        if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
  50            ((creds->uid == cred->uid   || creds->uid == cred->euid ||
  51              creds->uid == cred->suid) || capable(CAP_SETUID)) &&
  52            ((creds->gid == cred->gid   || creds->gid == cred->egid ||
  53              creds->gid == cred->sgid) || capable(CAP_SETGID))) {
  54               return 0;
  55        }
  56        return -EPERM;
  57}
  58
  59static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  60{
  61        int *fdp = (int*)CMSG_DATA(cmsg);
  62        struct scm_fp_list *fpl = *fplp;
  63        struct file **fpp;
  64        int i, num;
  65
  66        num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  67
  68        if (num <= 0)
  69                return 0;
  70
  71        if (num > SCM_MAX_FD)
  72                return -EINVAL;
  73
  74        if (!fpl)
  75        {
  76                fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  77                if (!fpl)
  78                        return -ENOMEM;
  79                *fplp = fpl;
  80                fpl->count = 0;
  81                fpl->max = SCM_MAX_FD;
  82        }
  83        fpp = &fpl->fp[fpl->count];
  84
  85        if (fpl->count + num > fpl->max)
  86                return -EINVAL;
  87
  88        /*
  89         *      Verify the descriptors and increment the usage count.
  90         */
  91
  92        for (i=0; i< num; i++)
  93        {
  94                int fd = fdp[i];
  95                struct file *file;
  96
  97                if (fd < 0 || !(file = fget_raw(fd)))
  98                        return -EBADF;
  99                *fpp++ = file;
 100                fpl->count++;
 101        }
 102        return num;
 103}
 104
 105void __scm_destroy(struct scm_cookie *scm)
 106{
 107        struct scm_fp_list *fpl = scm->fp;
 108        int i;
 109
 110        if (fpl) {
 111                scm->fp = NULL;
 112                for (i=fpl->count-1; i>=0; i--)
 113                        fput(fpl->fp[i]);
 114                kfree(fpl);
 115        }
 116}
 117EXPORT_SYMBOL(__scm_destroy);
 118
 119int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 120{
 121        struct cmsghdr *cmsg;
 122        int err;
 123
 124        for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 125        {
 126                err = -EINVAL;
 127
 128                /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 129                /* The first check was omitted in <= 2.2.5. The reasoning was
 130                   that parser checks cmsg_len in any case, so that
 131                   additional check would be work duplication.
 132                   But if cmsg_level is not SOL_SOCKET, we do not check
 133                   for too short ancillary data object at all! Oops.
 134                   OK, let's add it...
 135                 */
 136                if (!CMSG_OK(msg, cmsg))
 137                        goto error;
 138
 139                if (cmsg->cmsg_level != SOL_SOCKET)
 140                        continue;
 141
 142                switch (cmsg->cmsg_type)
 143                {
 144                case SCM_RIGHTS:
 145                        if (!sock->ops || sock->ops->family != PF_UNIX)
 146                                goto error;
 147                        err=scm_fp_copy(cmsg, &p->fp);
 148                        if (err<0)
 149                                goto error;
 150                        break;
 151                case SCM_CREDENTIALS:
 152                        if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 153                                goto error;
 154                        memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 155                        err = scm_check_creds(&p->creds);
 156                        if (err)
 157                                goto error;
 158
 159                        if (!p->pid || pid_vnr(p->pid) != p->creds.pid) {
 160                                struct pid *pid;
 161                                err = -ESRCH;
 162                                pid = find_get_pid(p->creds.pid);
 163                                if (!pid)
 164                                        goto error;
 165                                put_pid(p->pid);
 166                                p->pid = pid;
 167                        }
 168
 169                        if (!p->cred ||
 170                            (p->cred->euid != p->creds.uid) ||
 171                            (p->cred->egid != p->creds.gid)) {
 172                                struct cred *cred;
 173                                err = -ENOMEM;
 174                                cred = prepare_creds();
 175                                if (!cred)
 176                                        goto error;
 177
 178                                cred->uid = cred->euid = p->creds.uid;
 179                                cred->gid = cred->egid = p->creds.gid;
 180                                if (p->cred)
 181                                        put_cred(p->cred);
 182                                p->cred = cred;
 183                        }
 184                        break;
 185                default:
 186                        goto error;
 187                }
 188        }
 189
 190        if (p->fp && !p->fp->count)
 191        {
 192                kfree(p->fp);
 193                p->fp = NULL;
 194        }
 195        return 0;
 196
 197error:
 198        scm_destroy(p);
 199        return err;
 200}
 201EXPORT_SYMBOL(__scm_send);
 202
 203int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 204{
 205        struct cmsghdr __user *cm
 206                = (__force struct cmsghdr __user *)msg->msg_control;
 207        struct cmsghdr cmhdr;
 208        int cmlen = CMSG_LEN(len);
 209        int err;
 210
 211        if (MSG_CMSG_COMPAT & msg->msg_flags)
 212                return put_cmsg_compat(msg, level, type, len, data);
 213
 214        if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 215                msg->msg_flags |= MSG_CTRUNC;
 216                return 0; /* XXX: return error? check spec. */
 217        }
 218        if (msg->msg_controllen < cmlen) {
 219                msg->msg_flags |= MSG_CTRUNC;
 220                cmlen = msg->msg_controllen;
 221        }
 222        cmhdr.cmsg_level = level;
 223        cmhdr.cmsg_type = type;
 224        cmhdr.cmsg_len = cmlen;
 225
 226        err = -EFAULT;
 227        if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 228                goto out;
 229        if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 230                goto out;
 231        cmlen = CMSG_SPACE(len);
 232        if (msg->msg_controllen < cmlen)
 233                cmlen = msg->msg_controllen;
 234        msg->msg_control += cmlen;
 235        msg->msg_controllen -= cmlen;
 236        err = 0;
 237out:
 238        return err;
 239}
 240EXPORT_SYMBOL(put_cmsg);
 241
 242void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 243{
 244        struct cmsghdr __user *cm
 245                = (__force struct cmsghdr __user*)msg->msg_control;
 246
 247        int fdmax = 0;
 248        int fdnum = scm->fp->count;
 249        struct file **fp = scm->fp->fp;
 250        int __user *cmfptr;
 251        int err = 0, i;
 252
 253        if (MSG_CMSG_COMPAT & msg->msg_flags) {
 254                scm_detach_fds_compat(msg, scm);
 255                return;
 256        }
 257
 258        if (msg->msg_controllen > sizeof(struct cmsghdr))
 259                fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 260                         / sizeof(int));
 261
 262        if (fdnum < fdmax)
 263                fdmax = fdnum;
 264
 265        for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 266             i++, cmfptr++)
 267        {
 268                struct socket *sock;
 269                int new_fd;
 270                err = security_file_receive(fp[i]);
 271                if (err)
 272                        break;
 273                err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 274                                          ? O_CLOEXEC : 0);
 275                if (err < 0)
 276                        break;
 277                new_fd = err;
 278                err = put_user(new_fd, cmfptr);
 279                if (err) {
 280                        put_unused_fd(new_fd);
 281                        break;
 282                }
 283                /* Bump the usage count and install the file. */
 284                get_file(fp[i]);
 285                sock = sock_from_file(fp[i], &err);
 286                if (sock)
 287                        sock_update_netprioidx(sock->sk, current);
 288                fd_install(new_fd, fp[i]);
 289        }
 290
 291        if (i > 0)
 292        {
 293                int cmlen = CMSG_LEN(i*sizeof(int));
 294                err = put_user(SOL_SOCKET, &cm->cmsg_level);
 295                if (!err)
 296                        err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 297                if (!err)
 298                        err = put_user(cmlen, &cm->cmsg_len);
 299                if (!err) {
 300                        cmlen = CMSG_SPACE(i*sizeof(int));
 301                        msg->msg_control += cmlen;
 302                        msg->msg_controllen -= cmlen;
 303                }
 304        }
 305        if (i < fdnum || (fdnum && fdmax <= 0))
 306                msg->msg_flags |= MSG_CTRUNC;
 307
 308        /*
 309         * All of the files that fit in the message have had their
 310         * usage counts incremented, so we just free the list.
 311         */
 312        __scm_destroy(scm);
 313}
 314EXPORT_SYMBOL(scm_detach_fds);
 315
 316struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 317{
 318        struct scm_fp_list *new_fpl;
 319        int i;
 320
 321        if (!fpl)
 322                return NULL;
 323
 324        new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 325                          GFP_KERNEL);
 326        if (new_fpl) {
 327                for (i = 0; i < fpl->count; i++)
 328                        get_file(fpl->fp[i]);
 329                new_fpl->max = new_fpl->count;
 330        }
 331        return new_fpl;
 332}
 333EXPORT_SYMBOL(scm_fp_dup);
 334
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