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 #include <linux/io_uring.h>
  30
  31 #include <linux/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 #include <net/cls_cgroup.h>
  39
  40
  41 /*
  42  *      Only allow a user to send credentials, that they could set with
  43  *      setu(g)id.
  44  */
  45
  46 static __inline__ int scm_check_creds(struct ucred *creds)
  47 {
  48         const struct cred *cred = current_cred();
  49         kuid_t uid = make_kuid(cred->user_ns, creds->uid);
  50         kgid_t gid = make_kgid(cred->user_ns, creds->gid);
  51
  52         if (!uid_valid(uid) || !gid_valid(gid))
  53                 return -EINVAL;
  54
  55         if ((creds->pid == task_tgid_vnr(current) ||
  56              ns_capable(task_active_pid_ns(current)->user_ns, CAP_SYS_ADMIN)) &&
  57             ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
  58               uid_eq(uid, cred->suid)) || ns_capable(cred->user_ns, CAP_SETUID)) &&
  59             ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
  60               gid_eq(gid, cred->sgid)) || ns_capable(cred->user_ns, CAP_SETGID))) {
  61                return 0;
  62         }
  63         return -EPERM;
  64 }
  65
  66 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  67 {
  68         int *fdp = (int*)CMSG_DATA(cmsg);
  69         struct scm_fp_list *fpl = *fplp;
  70         struct file **fpp;
  71         int i, num;
  72
  73         num = (cmsg->cmsg_len - sizeof(struct cmsghdr))/sizeof(int);
  74
  75         if (num <= 0)
  76                 return 0;
  77
  78         if (num > SCM_MAX_FD)
  79                 return -EINVAL;
  80
  81         if (!fpl)
  82         {
  83                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL_ACCOUNT);
  84                 if (!fpl)
  85                         return -ENOMEM;
  86                 *fplp = fpl;
  87                 fpl->count = 0;
  88                 fpl->max = SCM_MAX_FD;
  89                 fpl->user = NULL;
  90         }
  91         fpp = &fpl->fp[fpl->count];
  92
  93         if (fpl->count + num > fpl->max)
  94                 return -EINVAL;
  95
  96         /*
  97          *      Verify the descriptors and increment the usage count.
  98          */
  99
 100         for (i=0; i< num; i++)
 101         {
 102                 int fd = fdp[i];
 103                 struct file *file;
 104
 105                 if (fd < 0 || !(file = fget_raw(fd)))
 106                         return -EBADF;
 107                 /* don't allow io_uring files */
 108                 if (io_is_uring_fops(file)) {
 109                         fput(file);
 110                         return -EINVAL;
 111                 }
 112                 *fpp++ = file;
 113                 fpl->count++;
 114         }
 115
 116         if (!fpl->user)
 117                 fpl->user = get_uid(current_user());
 118
 119         return num;
 120 }
 121
 122 void __scm_destroy(struct scm_cookie *scm)
 123 {
 124         struct scm_fp_list *fpl = scm->fp;
 125         int i;
 126
 127         if (fpl) {
 128                 scm->fp = NULL;
 129                 for (i=fpl->count-1; i>=0; i--)
 130                         fput(fpl->fp[i]);
 131                 free_uid(fpl->user);
 132                 kfree(fpl);
 133         }
 134 }
 135 EXPORT_SYMBOL(__scm_destroy);
 136
 137 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 138 {
 139         struct cmsghdr *cmsg;
 140         int err;
 141
 142         for_each_cmsghdr(cmsg, msg) {
 143                 err = -EINVAL;
 144
 145                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 146                 /* The first check was omitted in <= 2.2.5. The reasoning was
 147                    that parser checks cmsg_len in any case, so that
 148                    additional check would be work duplication.
 149                    But if cmsg_level is not SOL_SOCKET, we do not check
 150                    for too short ancillary data object at all! Oops.
 151                    OK, let's add it...
 152                  */
 153                 if (!CMSG_OK(msg, cmsg))
 154                         goto error;
 155
 156                 if (cmsg->cmsg_level != SOL_SOCKET)
 157                         continue;
 158
 159                 switch (cmsg->cmsg_type)
 160                 {
 161                 case SCM_RIGHTS:
 162                         if (!sock->ops || sock->ops->family != PF_UNIX)
 163                                 goto error;
 164                         err=scm_fp_copy(cmsg, &p->fp);
 165                         if (err<0)
 166                                 goto error;
 167                         break;
 168                 case SCM_CREDENTIALS:
 169                 {
 170                         struct ucred creds;
 171                         kuid_t uid;
 172                         kgid_t gid;
 173                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 174                                 goto error;
 175                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 176                         err = scm_check_creds(&creds);
 177                         if (err)
 178                                 goto error;
 179
 180                         p->creds.pid = creds.pid;
 181                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 182                                 struct pid *pid;
 183                                 err = -ESRCH;
 184                                 pid = find_get_pid(creds.pid);
 185                                 if (!pid)
 186                                         goto error;
 187                                 put_pid(p->pid);
 188                                 p->pid = pid;
 189                         }
 190
 191                         err = -EINVAL;
 192                         uid = make_kuid(current_user_ns(), creds.uid);
 193                         gid = make_kgid(current_user_ns(), creds.gid);
 194                         if (!uid_valid(uid) || !gid_valid(gid))
 195                                 goto error;
 196
 197                         p->creds.uid = uid;
 198                         p->creds.gid = gid;
 199                         break;
 200                 }
 201                 default:
 202                         goto error;
 203                 }
 204         }
 205
 206         if (p->fp && !p->fp->count)
 207         {
 208                 kfree(p->fp);
 209                 p->fp = NULL;
 210         }
 211         return 0;
 212
 213 error:
 214         scm_destroy(p);
 215         return err;
 216 }
 217 EXPORT_SYMBOL(__scm_send);
 218
 219 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 220 {
 221         int cmlen = CMSG_LEN(len);
 222
 223         if (msg->msg_flags & MSG_CMSG_COMPAT)
 224                 return put_cmsg_compat(msg, level, type, len, data);
 225
 226         if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
 227                 msg->msg_flags |= MSG_CTRUNC;
 228                 return 0; /* XXX: return error? check spec. */
 229         }
 230         if (msg->msg_controllen < cmlen) {
 231                 msg->msg_flags |= MSG_CTRUNC;
 232                 cmlen = msg->msg_controllen;
 233         }
 234
 235         if (msg->msg_control_is_user) {
 236                 struct cmsghdr __user *cm = msg->msg_control_user;
 237
 238                 check_object_size(data, cmlen - sizeof(*cm), true);
 239
 240                 if (!user_write_access_begin(cm, cmlen))
 241                         goto efault;
 242
 243                 unsafe_put_user(cmlen, &cm->cmsg_len, efault_end);
 244                 unsafe_put_user(level, &cm->cmsg_level, efault_end);
 245                 unsafe_put_user(type, &cm->cmsg_type, efault_end);
 246                 unsafe_copy_to_user(CMSG_USER_DATA(cm), data,
 247                                     cmlen - sizeof(*cm), efault_end);
 248                 user_write_access_end();
 249         } else {
 250                 struct cmsghdr *cm = msg->msg_control;
 251
 252                 cm->cmsg_level = level;
 253                 cm->cmsg_type = type;
 254                 cm->cmsg_len = cmlen;
 255                 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
 256         }
 257
 258         cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
 259         msg->msg_control += cmlen;
 260         msg->msg_controllen -= cmlen;
 261         return 0;
 262
 263 efault_end:
 264         user_write_access_end();
 265 efault:
 266         return -EFAULT;
 267 }
 268 EXPORT_SYMBOL(put_cmsg);
 269
 270 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 271 {
 272         struct scm_timestamping64 tss;
 273         int i;
 274
 275         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 276                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 277                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 278         }
 279
 280         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
 281 }
 282 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
 283
 284 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 285 {
 286         struct scm_timestamping tss;
 287         int i;
 288
 289         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 290                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 291                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 292         }
 293
 294         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
 295 }
 296 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
 297
 298 static int scm_max_fds(struct msghdr *msg)
 299 {
 300         if (msg->msg_controllen <= sizeof(struct cmsghdr))
 301                 return 0;
 302         return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
 303 }
 304
 305 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 306 {
 307         struct cmsghdr __user *cm =
 308                 (__force struct cmsghdr __user *)msg->msg_control;
 309         unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
 310         int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
 311         int __user *cmsg_data = CMSG_USER_DATA(cm);
 312         int err = 0, i;
 313
 314         /* no use for FD passing from kernel space callers */
 315         if (WARN_ON_ONCE(!msg->msg_control_is_user))
 316                 return;
 317
 318         if (msg->msg_flags & MSG_CMSG_COMPAT) {
 319                 scm_detach_fds_compat(msg, scm);
 320                 return;
 321         }
 322
 323         for (i = 0; i < fdmax; i++) {
 324                 err = receive_fd_user(scm->fp->fp[i], cmsg_data + i, o_flags);
 325                 if (err < 0)
 326                         break;
 327         }
 328
 329         if (i > 0) {
 330                 int cmlen = CMSG_LEN(i * sizeof(int));
 331
 332                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 333                 if (!err)
 334                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 335                 if (!err)
 336                         err = put_user(cmlen, &cm->cmsg_len);
 337                 if (!err) {
 338                         cmlen = CMSG_SPACE(i * sizeof(int));
 339                         if (msg->msg_controllen < cmlen)
 340                                 cmlen = msg->msg_controllen;
 341                         msg->msg_control += cmlen;
 342                         msg->msg_controllen -= cmlen;
 343                 }
 344         }
 345
 346         if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
 347                 msg->msg_flags |= MSG_CTRUNC;
 348
 349         /*
 350          * All of the files that fit in the message have had their usage counts
 351          * incremented, so we just free the list.
 352          */
 353         __scm_destroy(scm);
 354 }
 355 EXPORT_SYMBOL(scm_detach_fds);
 356
 357 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 358 {
 359         struct scm_fp_list *new_fpl;
 360         int i;
 361
 362         if (!fpl)
 363                 return NULL;
 364
 365         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 366                           GFP_KERNEL_ACCOUNT);
 367         if (new_fpl) {
 368                 for (i = 0; i < fpl->count; i++)
 369                         get_file(fpl->fp[i]);
 370                 new_fpl->max = new_fpl->count;
 371                 new_fpl->user = get_uid(fpl->user);
 372         }
 373         return new_fpl;
 374 }
 375 EXPORT_SYMBOL(scm_fp_dup);