net/core/scm.c

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