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/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
  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) || capable(CAP_SYS_ADMIN)) &&
  55             ((uid_eq(uid, cred->uid)   || uid_eq(uid, cred->euid) ||
  56               uid_eq(uid, cred->suid)) || capable(CAP_SETUID)) &&
  57             ((gid_eq(gid, cred->gid)   || gid_eq(gid, cred->egid) ||
  58               gid_eq(gid, cred->sgid)) || capable(CAP_SETGID))) {
  59                return 0;
  60         }
  61         return -EPERM;
  62 }
  63
  64 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  65 {
  66         int *fdp = (int*)CMSG_DATA(cmsg);
  67         struct scm_fp_list *fpl = *fplp;
  68         struct file **fpp;
  69         int i, num;
  70
  71         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  72
  73         if (num <= 0)
  74                 return 0;
  75
  76         if (num > SCM_MAX_FD)
  77                 return -EINVAL;
  78
  79         if (!fpl)
  80         {
  81                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  82                 if (!fpl)
  83                         return -ENOMEM;
  84                 *fplp = fpl;
  85                 fpl->count = 0;
  86                 fpl->max = SCM_MAX_FD;
  87         }
  88         fpp = &fpl->fp[fpl->count];
  89
  90         if (fpl->count + num > fpl->max)
  91                 return -EINVAL;
  92
  93         /*
  94          *      Verify the descriptors and increment the usage count.
  95          */
  96
  97         for (i=0; i< num; i++)
  98         {
  99                 int fd = fdp[i];
 100                 struct file *file;
 101
 102                 if (fd < 0 || !(file = fget_raw(fd)))
 103                         return -EBADF;
 104                 *fpp++ = file;
 105                 fpl->count++;
 106         }
 107         return num;
 108 }
 109
 110 void __scm_destroy(struct scm_cookie *scm)
 111 {
 112         struct scm_fp_list *fpl = scm->fp;
 113         int i;
 114
 115         if (fpl) {
 116                 scm->fp = NULL;
 117                 for (i=fpl->count-1; i>=0; i--)
 118                         fput(fpl->fp[i]);
 119                 kfree(fpl);
 120         }
 121 }
 122 EXPORT_SYMBOL(__scm_destroy);
 123
 124 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 125 {
 126         struct cmsghdr *cmsg;
 127         int err;
 128
 129         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 130         {
 131                 err = -EINVAL;
 132
 133                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 134                 /* The first check was omitted in <= 2.2.5. The reasoning was
 135                    that parser checks cmsg_len in any case, so that
 136                    additional check would be work duplication.
 137                    But if cmsg_level is not SOL_SOCKET, we do not check
 138                    for too short ancillary data object at all! Oops.
 139                    OK, let's add it...
 140                  */
 141                 if (!CMSG_OK(msg, cmsg))
 142                         goto error;
 143
 144                 if (cmsg->cmsg_level != SOL_SOCKET)
 145                         continue;
 146
 147                 switch (cmsg->cmsg_type)
 148                 {
 149                 case SCM_RIGHTS:
 150                         if (!sock->ops || sock->ops->family != PF_UNIX)
 151                                 goto error;
 152                         err=scm_fp_copy(cmsg, &p->fp);
 153                         if (err<0)
 154                                 goto error;
 155                         break;
 156                 case SCM_CREDENTIALS:
 157                 {
 158                         struct ucred creds;
 159                         kuid_t uid;
 160                         kgid_t gid;
 161                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 162                                 goto error;
 163                         memcpy(&creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 164                         err = scm_check_creds(&creds);
 165                         if (err)
 166                                 goto error;
 167
 168                         p->creds.pid = creds.pid;
 169                         if (!p->pid || pid_vnr(p->pid) != creds.pid) {
 170                                 struct pid *pid;
 171                                 err = -ESRCH;
 172                                 pid = find_get_pid(creds.pid);
 173                                 if (!pid)
 174                                         goto error;
 175                                 put_pid(p->pid);
 176                                 p->pid = pid;
 177                         }
 178
 179                         err = -EINVAL;
 180                         uid = make_kuid(current_user_ns(), creds.uid);
 181                         gid = make_kgid(current_user_ns(), creds.gid);
 182                         if (!uid_valid(uid) || !gid_valid(gid))
 183                                 goto error;
 184
 185                         p->creds.uid = uid;
 186                         p->creds.gid = gid;
 187
 188                         if (!p->cred ||
 189                             !uid_eq(p->cred->euid, uid) ||
 190                             !gid_eq(p->cred->egid, gid)) {
 191                                 struct cred *cred;
 192                                 err = -ENOMEM;
 193                                 cred = prepare_creds();
 194                                 if (!cred)
 195                                         goto error;
 196
 197                                 cred->uid = cred->euid = uid;
 198                                 cred->gid = cred->egid = gid;
 199                                 if (p->cred)
 200                                         put_cred(p->cred);
 201                                 p->cred = cred;
 202                         }
 203                         break;
 204                 }
 205                 default:
 206                         goto error;
 207                 }
 208         }
 209
 210         if (p->fp && !p->fp->count)
 211         {
 212                 kfree(p->fp);
 213                 p->fp = NULL;
 214         }
 215         return 0;
 216
 217 error:
 218         scm_destroy(p);
 219         return err;
 220 }
 221 EXPORT_SYMBOL(__scm_send);
 222
 223 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 224 {
 225         struct cmsghdr __user *cm
 226                 = (__force struct cmsghdr __user *)msg->msg_control;
 227         struct cmsghdr cmhdr;
 228         int cmlen = CMSG_LEN(len);
 229         int err;
 230
 231         if (MSG_CMSG_COMPAT & msg->msg_flags)
 232                 return put_cmsg_compat(msg, level, type, len, data);
 233
 234         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 235                 msg->msg_flags |= MSG_CTRUNC;
 236                 return 0; /* XXX: return error? check spec. */
 237         }
 238         if (msg->msg_controllen < cmlen) {
 239                 msg->msg_flags |= MSG_CTRUNC;
 240                 cmlen = msg->msg_controllen;
 241         }
 242         cmhdr.cmsg_level = level;
 243         cmhdr.cmsg_type = type;
 244         cmhdr.cmsg_len = cmlen;
 245
 246         err = -EFAULT;
 247         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 248                 goto out;
 249         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 250                 goto out;
 251         cmlen = CMSG_SPACE(len);
 252         if (msg->msg_controllen < cmlen)
 253                 cmlen = msg->msg_controllen;
 254         msg->msg_control += cmlen;
 255         msg->msg_controllen -= cmlen;
 256         err = 0;
 257 out:
 258         return err;
 259 }
 260 EXPORT_SYMBOL(put_cmsg);
 261
 262 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 263 {
 264         struct cmsghdr __user *cm
 265                 = (__force struct cmsghdr __user*)msg->msg_control;
 266
 267         int fdmax = 0;
 268         int fdnum = scm->fp->count;
 269         struct file **fp = scm->fp->fp;
 270         int __user *cmfptr;
 271         int err = 0, i;
 272
 273         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 274                 scm_detach_fds_compat(msg, scm);
 275                 return;
 276         }
 277
 278         if (msg->msg_controllen > sizeof(struct cmsghdr))
 279                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 280                          / sizeof(int));
 281
 282         if (fdnum < fdmax)
 283                 fdmax = fdnum;
 284
 285         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 286              i++, cmfptr++)
 287         {
 288                 struct socket *sock;
 289                 int new_fd;
 290                 err = security_file_receive(fp[i]);
 291                 if (err)
 292                         break;
 293                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 294                                           ? O_CLOEXEC : 0);
 295                 if (err < 0)
 296                         break;
 297                 new_fd = err;
 298                 err = put_user(new_fd, cmfptr);
 299                 if (err) {
 300                         put_unused_fd(new_fd);
 301                         break;
 302                 }
 303                 /* Bump the usage count and install the file. */
 304                 sock = sock_from_file(fp[i], &err);
 305                 if (sock)
 306                         sock_update_netprioidx(sock->sk, current);
 307                 fd_install(new_fd, get_file(fp[i]));
 308         }
 309
 310         if (i > 0)
 311         {
 312                 int cmlen = CMSG_LEN(i*sizeof(int));
 313                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 314                 if (!err)
 315                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 316                 if (!err)
 317                         err = put_user(cmlen, &cm->cmsg_len);
 318                 if (!err) {
 319                         cmlen = CMSG_SPACE(i*sizeof(int));
 320                         msg->msg_control += cmlen;
 321                         msg->msg_controllen -= cmlen;
 322                 }
 323         }
 324         if (i < fdnum || (fdnum && fdmax <= 0))
 325                 msg->msg_flags |= MSG_CTRUNC;
 326
 327         /*
 328          * All of the files that fit in the message have had their
 329          * usage counts incremented, so we just free the list.
 330          */
 331         __scm_destroy(scm);
 332 }
 333 EXPORT_SYMBOL(scm_detach_fds);
 334
 335 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 336 {
 337         struct scm_fp_list *new_fpl;
 338         int i;
 339
 340         if (!fpl)
 341                 return NULL;
 342
 343         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 344                           GFP_KERNEL);
 345         if (new_fpl) {
 346                 for (i = 0; i < fpl->count; i++)
 347                         get_file(fpl->fp[i]);
 348                 new_fpl->max = new_fpl->count;
 349         }
 350         return new_fpl;
 351 }
 352 EXPORT_SYMBOL(scm_fp_dup);