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);
  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         struct cmsghdr *cmsg;
 134         int err;
 135
 136         for_each_cmsghdr(cmsg, msg) {
 137                 err = -EINVAL;
 138
 139                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 140                 /* The first check was omitted in <= 2.2.5. The reasoning was
 141                    that parser checks cmsg_len in any case, so that
 142                    additional check would be work duplication.
 143                    But if cmsg_level is not SOL_SOCKET, we do not check
 144                    for too short ancillary data object at all! Oops.
 145                    OK, let's add it...
 146                  */
 147                 if (!CMSG_OK(msg, cmsg))
 148                         goto error;
 149
 150                 if (cmsg->cmsg_level != SOL_SOCKET)
 151                         continue;
 152
 153                 switch (cmsg->cmsg_type)
 154                 {
 155                 case SCM_RIGHTS:
 156                         if (!sock->ops || sock->ops->family != PF_UNIX)
 157                                 goto error;
 158                         err=scm_fp_copy(cmsg, &p->fp);
 159                         if (err<0)
 160                                 goto error;
 161                         break;
 162                 case SCM_CREDENTIALS:
 163                 {
 164                         struct ucred creds;
 165                         kuid_t uid;
 166                         kgid_t gid;
 167                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 168                                 goto error;
 169                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 170                         err = scm_check_creds(&creds);
 171                         if (err)
 172                                 goto error;
 173
 174                         p->creds.pid = creds.pid;
 175                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 176                                 struct pid *pid;
 177                                 err = -ESRCH;
 178                                 pid = find_get_pid(creds.pid);
 179                                 if (!pid)
 180                                         goto error;
 181                                 put_pid(p->pid);
 182                                 p->pid = pid;
 183                         }
 184
 185                         err = -EINVAL;
 186                         uid = make_kuid(current_user_ns(), creds.uid);
 187                         gid = make_kgid(current_user_ns(), creds.gid);
 188                         if (!uid_valid(uid) || !gid_valid(gid))
 189                                 goto error;
 190
 191                         p->creds.uid = uid;
 192                         p->creds.gid = gid;
 193                         break;
 194                 }
 195                 default:
 196                         goto error;
 197                 }
 198         }
 199
 200         if (p->fp && !p->fp->count)
 201         {
 202                 kfree(p->fp);
 203                 p->fp = NULL;
 204         }
 205         return 0;
 206
 207 error:
 208         scm_destroy(p);
 209         return err;
 210 }
 211 EXPORT_SYMBOL(__scm_send);
 212
 213 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 214 {
 215         int cmlen = CMSG_LEN(len);
 216
 217         if (msg->msg_flags & MSG_CMSG_COMPAT)
 218                 return put_cmsg_compat(msg, level, type, len, data);
 219
 220         if (!msg->msg_control || msg->msg_controllen < sizeof(struct cmsghdr)) {
 221                 msg->msg_flags |= MSG_CTRUNC;
 222                 return 0; /* XXX: return error? check spec. */
 223         }
 224         if (msg->msg_controllen < cmlen) {
 225                 msg->msg_flags |= MSG_CTRUNC;
 226                 cmlen = msg->msg_controllen;
 227         }
 228
 229         if (msg->msg_control_is_user) {
 230                 struct cmsghdr __user *cm = msg->msg_control_user;
 231                 struct cmsghdr cmhdr;
 232
 233                 cmhdr.cmsg_level = level;
 234                 cmhdr.cmsg_type = type;
 235                 cmhdr.cmsg_len = cmlen;
 236                 if (copy_to_user(cm, &cmhdr, sizeof cmhdr) ||
 237                     copy_to_user(CMSG_USER_DATA(cm), data, cmlen - sizeof(*cm)))
 238                         return -EFAULT;
 239         } else {
 240                 struct cmsghdr *cm = msg->msg_control;
 241
 242                 cm->cmsg_level = level;
 243                 cm->cmsg_type = type;
 244                 cm->cmsg_len = cmlen;
 245                 memcpy(CMSG_DATA(cm), data, cmlen - sizeof(*cm));
 246         }
 247
 248         cmlen = min(CMSG_SPACE(len), msg->msg_controllen);
 249         msg->msg_control += cmlen;
 250         msg->msg_controllen -= cmlen;
 251         return 0;
 252 }
 253 EXPORT_SYMBOL(put_cmsg);
 254
 255 void put_cmsg_scm_timestamping64(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 256 {
 257         struct scm_timestamping64 tss;
 258         int i;
 259
 260         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 261                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 262                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 263         }
 264
 265         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_NEW, sizeof(tss), &tss);
 266 }
 267 EXPORT_SYMBOL(put_cmsg_scm_timestamping64);
 268
 269 void put_cmsg_scm_timestamping(struct msghdr *msg, struct scm_timestamping_internal *tss_internal)
 270 {
 271         struct scm_timestamping tss;
 272         int i;
 273
 274         for (i = 0; i < ARRAY_SIZE(tss.ts); i++) {
 275                 tss.ts[i].tv_sec = tss_internal->ts[i].tv_sec;
 276                 tss.ts[i].tv_nsec = tss_internal->ts[i].tv_nsec;
 277         }
 278
 279         put_cmsg(msg, SOL_SOCKET, SO_TIMESTAMPING_OLD, sizeof(tss), &tss);
 280 }
 281 EXPORT_SYMBOL(put_cmsg_scm_timestamping);
 282
 283 static int scm_max_fds(struct msghdr *msg)
 284 {
 285         if (msg->msg_controllen <= sizeof(struct cmsghdr))
 286                 return 0;
 287         return (msg->msg_controllen - sizeof(struct cmsghdr)) / sizeof(int);
 288 }
 289
 290 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 291 {
 292         struct cmsghdr __user *cm =
 293                 (__force struct cmsghdr __user *)msg->msg_control;
 294         unsigned int o_flags = (msg->msg_flags & MSG_CMSG_CLOEXEC) ? O_CLOEXEC : 0;
 295         int fdmax = min_t(int, scm_max_fds(msg), scm->fp->count);
 296         int __user *cmsg_data = CMSG_USER_DATA(cm);
 297         int err = 0, i;
 298
 299         /* no use for FD passing from kernel space callers */
 300         if (WARN_ON_ONCE(!msg->msg_control_is_user))
 301                 return;
 302
 303         if (msg->msg_flags & MSG_CMSG_COMPAT) {
 304                 scm_detach_fds_compat(msg, scm);
 305                 return;
 306         }
 307
 308         for (i = 0; i < fdmax; i++) {
 309                 err = receive_fd_user(scm->fp->fp[i], cmsg_data + i, o_flags);
 310                 if (err < 0)
 311                         break;
 312         }
 313
 314         if (i > 0) {
 315                 int cmlen = CMSG_LEN(i * sizeof(int));
 316
 317                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 318                 if (!err)
 319                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 320                 if (!err)
 321                         err = put_user(cmlen, &cm->cmsg_len);
 322                 if (!err) {
 323                         cmlen = CMSG_SPACE(i * sizeof(int));
 324                         if (msg->msg_controllen < cmlen)
 325                                 cmlen = msg->msg_controllen;
 326                         msg->msg_control += cmlen;
 327                         msg->msg_controllen -= cmlen;
 328                 }
 329         }
 330
 331         if (i < scm->fp->count || (scm->fp->count && fdmax <= 0))
 332                 msg->msg_flags |= MSG_CTRUNC;
 333
 334         /*
 335          * All of the files that fit in the message have had their usage counts
 336          * incremented, so we just free the list.
 337          */
 338         __scm_destroy(scm);
 339 }
 340 EXPORT_SYMBOL(scm_detach_fds);
 341
 342 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 343 {
 344         struct scm_fp_list *new_fpl;
 345         int i;
 346
 347         if (!fpl)
 348                 return NULL;
 349
 350         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 351                           GFP_KERNEL);
 352         if (new_fpl) {
 353                 for (i = 0; i < fpl->count; i++)
 354                         get_file(fpl->fp[i]);
 355                 new_fpl->max = new_fpl->count;
 356                 new_fpl->user = get_uid(fpl->user);
 357         }
 358         return new_fpl;
 359 }
 360 EXPORT_SYMBOL(scm_fp_dup);