net/core/scm.c

   1 // SPDX-License-Identifier: GPL-2.0-or-later
   2 /* scm.c - Socket level control messages processing.
   3  *
   4  * Author:      Alexey Kuznetsov, <kuznet@ms2.inr.ac.ru>
   5  *              Alignment and value checking mods by Craig Metz
   6  */
   7
   8 #include <linux/module.h>
   9 #include <linux/signal.h>
  10 #include <linux/capability.h>
  11 #include <linux/errno.h>
  12 #include <linux/sched.h>
  13 #include <linux/sched/user.h>
  14 #include <linux/mm.h>
  15 #include <linux/kernel.h>
  16 #include <linux/stat.h>
  17 #include <linux/socket.h>
  18 #include <linux/file.h>
  19 #include <linux/fcntl.h>
  20 #include <linux/net.h>
  21 #include <linux/interrupt.h>
  22 #include <linux/netdevice.h>
  23 #include <linux/security.h>
  24 #include <linux/pid_namespace.h>
  25 #include <linux/pid.h>
  26 #include <linux/nsproxy.h>
  27 #include <linux/slab.h>
  28 #include <linux/errqueue.h>
  29
  30 #include <linux/uaccess.h>
  31
  32 #include <net/protocol.h>
  33 #include <linux/skbuff.h>
  34 #include <net/sock.h>
  35 #include <net/compat.h>
  36 #include <net/scm.h>
  37 #include <net/cls_cgroup.h>
  38
  39
  40 /*
  41  *      Only allow a user to send credentials, that they could set with
  42  *      setu(g)id.
  43  */
  44
  45 static __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) ||
  55              ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
  56             ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
  57               uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
  58             ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
  59               gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
  60                return 0;
  61         }
  62         return -EPERM;
  63 }
  64
  65 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  66 {
  67         int *fdp = (int*)CMSG_DATA(cmsg);
  68         struct scm_fp_list *fpl = *fplp;
  69         struct file **fpp;
  70         int i, num;
  71
  72         num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);
  73
  74         if (num <= 0)
  75                 return 0;
  76
  77         if (num > SCM_MAX_FD)
  78                 return -EINVAL;
  79
  80         if (!fpl)
  81         {
  82                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL_ACCOUNT);
  83                 if (!fpl)
  84                         return -ENOMEM;
  85                 *fplp = fpl;
  86                 fpl->count = 0;
  87                 fpl->max = SCM_MAX_FD;
  88                 fpl->user = NULL;
  89         }
  90         fpp = &fpl->fp[fpl->count];
  91
  92         if (fpl->count + num > fpl->max)
  93                 return -EINVAL;
  94
  95         /*
  96          *      Verify the descriptors and increment the usage count.
  97          */
  98
  99         for (i=0; i< num; i++)
 100         {
 101                 int fd = fdp[i];
 102                 struct file *file;
 103
 104                 if (fd < 0 || !(file = fget_raw(fd)))
 105                         return -EBADF;
 106                 *fpp++ = file;
 107                 fpl->count++;
 108         }
 109
 110         if (!fpl->user)
 111                 fpl->user = get_uid(current_user());
 112
 113         return num;
 114 }
 115
 116 void __scm_destroy(struct scm_cookie *scm)
 117 {
 118         struct scm_fp_list *fpl = scm->fp;
 119         int i;
 120
 121         if (fpl) {
 122                 scm->fp = NULL;
 123                 for (i=fpl->count-1; i>=0; i--)
 124                         fput(fpl->fp[i]);
 125                 free_uid(fpl->user);
 126                 kfree(fpl);
 127         }
 128 }
 129 EXPORT_SYMBOL(__scm_destroy);
 130
 131 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 132 {
 133         const struct proto_ops *ops = READ_ONCE(sock->ops);
 134         struct cmsghdr *cmsg;
 135         int err;
 136
 137         for_each_cmsghdr(cmsg, msg) {
 138                 err = -EINVAL;
 139
 140                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 141                 /* The first check was omitted in <= 2.2.5. The reasoning was
 142                    that parser checks cmsg_len in any case, so that
 143                    additional check would be work duplication.
 144                    But if cmsg_level is not SOL_SOCKET, we do not check
 145                    for too short ancillary data object at all! Oops.
 146                    OK, let's add it...
 147                  */
 148                 if (!CMSG_OK(msg, cmsg))
 149                         goto error;
 150
 151                 if (cmsg->cmsg_level != SOL_SOCKET)
 152                         continue;
 153
 154                 switch (cmsg->cmsg_type)
 155                 {
 156                 case SCM_RIGHTS:
 157                         if (!ops || ops->family != PF_UNIX)
 158                                 goto error;
 159                         err=scm_fp_copy(cmsg, &p->fp);
 160                         if (err<0)
 161                                 goto error;
 162                         break;
 163                 case SCM_CREDENTIALS:
 164                 {
 165                         struct ucred creds;
 166                         kuid_t uid;
 167                         kgid_t gid;
 168                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 169                                 goto error;
 170                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 171                         err = scm_check_creds(&creds);
 172                         if (err)
 173                                 goto error;
 174
 175                         p->creds.pid = creds.pid;
 176                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 177                                 struct pid *pid;
 178                                 err = -ESRCH;
 179                                 pid = find_get_pid(creds.pid);
 180                                 if (!pid)
 181                                         goto error;
 182                                 put_pid(p->pid);
 183                                 p->pid = pid;
 184                         }
 185
 186                         err = -EINVAL;
 187                         uid = make_kuid(current_user_ns(), creds.uid);
 188                         gid = make_kgid(current_user_ns(), creds.gid);
 189                         if (!uid_valid(uid) || !gid_valid(gid))
 190                                 goto error;
 191
 192                         p->creds.uid = uid;
 193                         p->creds.gid = gid;
 194                         break;
 195                 }
 196                 default:
 197                         goto error;
 198                 }
 199         }
 200
 201         if (p->fp && !p->fp->count)
 202         {
 203                 kfree(p->fp);
 204                 p->fp = NULL;
 205         }
 206         return 0;
 207
 208 error:
 209         scm_destroy(p);
 210         return err;
 211 }
 212 EXPORT_SYMBOL(__scm_send);
 213
 214 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 215 {
 216         int cmlen = CMSG_LEN(len);
 217
 218         if (msg->msg_flags & MSG_CMSG_COMPAT)
 219                 return put_cmsg_compat(msg, level, type, len, data);
 220
 221         if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
 222                 msg->msg_flags |= MSG_CTRUNC;
 223                 return 0; /* XXX: return error? check spec. */
 224         }
 225         if (msg->msg_controllen < cmlen) {
 226                 msg->msg_flags |= MSG_CTRUNC;
 227                 cmlen = msg->msg_controllen;
 228         }
 229
 230         if (msg->msg_control_is_user) {
 231                 struct cmsghdr __user *cm = msg->msg_control_user;
 232
 233                 check_object_size(data, cmlen - sizeof(*cm), true);
 234
 235                 if (!user_write_access_begin(cm, cmlen))
 236                         goto efault;
 237
 238                 unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
 239                 unsafe_put_user(level, &cm->cmsg_level, efault_end);
 240                 unsafe_put_user(type, &cm->cmsg_type, efault_end);
 241                 unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
 242                                     cmlen - sizeof(*cm), efault_end);
 243                 user_write_access_end();
 244         } else {
 245                 struct cmsghdr *cm = msg->msg_control;
 246
 247                 cm->cmsg_level = level;
 248                 cm->cmsg_type = type;
 249                 cm->cmsg_len = cmlen;
 250                 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
 251         }
 252
 253         cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
 254         if (msg->msg_control_is_user)
 255                 msg->msg_control_user += cmlen;
 256         else
 257                 msg->msg_control += cmlen;
 258         msg->msg_controllen -= cmlen;
 259         return 0;
 260
 261 efault_end:
 262         user_write_access_end();
 263 efault:
 264         return -EFAULT;
 265 }
 266 EXPORT_SYMBOL(put_cmsg);
 267
 268 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 269 {
 270         struct scm_timestamping64 tss;
 271         int i;
 272
 273         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 274                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 275                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 276         }
 277
 278         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
 279 }
 280 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
 281
 282 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 283 {
 284         struct scm_timestamping tss;
 285         int i;
 286
 287         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 288                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 289                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 290         }
 291
 292         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
 293 }
 294 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
 295
 296 static int scm_max_fds(struct msghdr *msg)
 297 {
 298         if (msg->msg_controllen <= sizeof(struct cmsghdr))
 299                 return 0;
 300         return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
 301 }
 302
 303 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 304 {
 305         struct cmsghdr __user *cm =
 306                 (__force struct cmsghdr __user *)msg->msg_control_user;
 307         unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
 308         int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
 309         int __user *cmsg_data = CMSG_USER_DATA(cm);
 310         int err = 0, i;
 311
 312         /* no use for FD passing from kernel space callers */
 313         if (WARN_ON_ONCE(!msg->msg_control_is_user))
 314                 return;
 315
 316         if (msg->msg_flags & MSG_CMSG_COMPAT) {
 317                 scm_detach_fds_compat(msg, scm);
 318                 return;
 319         }
 320
 321         for (i = 0; i < fdmax; i++) {
 322                 err = receive_fd_user(scm->fp->fp[i], cmsg_data + i, o_flags);
 323                 if (err < 0)
 324                         break;
 325         }
 326
 327         if (i > 0) {
 328                 int cmlen = CMSG_LEN(i * sizeof(int));
 329
 330                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 331                 if (!err)
 332                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 333                 if (!err)
 334                         err = put_user(cmlen, &cm->cmsg_len);
 335                 if (!err) {
 336                         cmlen = CMSG_SPACE(i * sizeof(int));
 337                         if (msg->msg_controllen < cmlen)
 338                                 cmlen = msg->msg_controllen;
 339                         msg->msg_control_user += cmlen;
 340                         msg->msg_controllen -= cmlen;
 341                 }
 342         }
 343
 344         if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
 345                 msg->msg_flags |= MSG_CTRUNC;
 346
 347         /*
 348          * All of the files that fit in the message have had their usage counts
 349          * incremented, so we just free the list.
 350          */
 351         __scm_destroy(scm);
 352 }
 353 EXPORT_SYMBOL(scm_detach_fds);
 354
 355 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 356 {
 357         struct scm_fp_list *new_fpl;
 358         int i;
 359
 360         if (!fpl)
 361                 return NULL;
 362
 363         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 364                           GFP_KERNEL_ACCOUNT);
 365         if (new_fpl) {
 366                 for (i = 0; i < fpl->count; i++)
 367                         get_file(fpl->fp[i]);
 368                 new_fpl->max = new_fpl->count;
 369                 new_fpl->user = get_uid(fpl->user);
 370         }
 371         return new_fpl;
 372 }
 373 EXPORT_SYMBOL(scm_fp_dup);