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/system.h>
  32 #include <asm/uaccess.h>
  33
  34 #include <net/protocol.h>
  35 #include <linux/skbuff.h>
  36 #include <net/sock.h>
  37 #include <net/compat.h>
  38 #include <net/scm.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
  50         if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
  51             ((creds->uid == cred->uid   || creds->uid == cred->euid ||
  52               creds->uid == cred->suid) || capable(CAP_SETUID)) &&
  53             ((creds->gid == cred->gid   || creds->gid == cred->egid ||
  54               creds->gid == cred->sgid) || capable(CAP_SETGID))) {
  55                return 0;
  56         }
  57         return -EPERM;
  58 }
  59
  60 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  61 {
  62         int *fdp = (int*)CMSG_DATA(cmsg);
  63         struct scm_fp_list *fpl = *fplp;
  64         struct file **fpp;
  65         int i, num;
  66
  67         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  68
  69         if (num <= 0)
  70                 return 0;
  71
  72         if (num > SCM_MAX_FD)
  73                 return -EINVAL;
  74
  75         if (!fpl)
  76         {
  77                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  78                 if (!fpl)
  79                         return -ENOMEM;
  80                 *fplp = fpl;
  81                 fpl->count = 0;
  82                 fpl->max = SCM_MAX_FD;
  83         }
  84         fpp = &fpl->fp[fpl->count];
  85
  86         if (fpl->count + num > fpl->max)
  87                 return -EINVAL;
  88
  89         /*
  90          *      Verify the descriptors and increment the usage count.
  91          */
  92
  93         for (i=0; i< num; i++)
  94         {
  95                 int fd = fdp[i];
  96                 struct file *file;
  97
  98                 if (fd < 0 || !(file = fget(fd)))
  99                         return -EBADF;
 100                 *fpp++ = file;
 101                 fpl->count++;
 102         }
 103         return num;
 104 }
 105
 106 void __scm_destroy(struct scm_cookie *scm)
 107 {
 108         struct scm_fp_list *fpl = scm->fp;
 109         int i;
 110
 111         if (fpl) {
 112                 scm->fp = NULL;
 113                 if (current->scm_work_list) {
 114                         list_add_tail(&fpl->list, current->scm_work_list);
 115                 } else {
 116                         LIST_HEAD(work_list);
 117
 118                         current->scm_work_list = &work_list;
 119
 120                         list_add(&fpl->list, &work_list);
 121                         while (!list_empty(&work_list)) {
 122                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 123
 124                                 list_del(&fpl->list);
 125                                 for (i=fpl->count-1; i>=0; i--)
 126                                         fput(fpl->fp[i]);
 127                                 kfree(fpl);
 128                         }
 129
 130                         current->scm_work_list = NULL;
 131                 }
 132         }
 133 }
 134 EXPORT_SYMBOL(__scm_destroy);
 135
 136 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 137 {
 138         struct cmsghdr *cmsg;
 139         int err;
 140
 141         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 142         {
 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                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 170                                 goto error;
 171                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 172                         err = scm_check_creds(&p->creds);
 173                         if (err)
 174                                 goto error;
 175
 176                         if (pid_vnr(p->pid) != p->creds.pid) {
 177                                 struct pid *pid;
 178                                 err = -ESRCH;
 179                                 pid = find_get_pid(p->creds.pid);
 180                                 if (!pid)
 181                                         goto error;
 182                                 put_pid(p->pid);
 183                                 p->pid = pid;
 184                         }
 185
 186                         if ((p->cred->euid != p->creds.uid) ||
 187                                 (p->cred->egid != p->creds.gid)) {
 188                                 struct cred *cred;
 189                                 err = -ENOMEM;
 190                                 cred = prepare_creds();
 191                                 if (!cred)
 192                                         goto error;
 193
 194                                 cred->uid = cred->euid = p->creds.uid;
 195                                 cred->gid = cred->egid = p->creds.uid;
 196                                 put_cred(p->cred);
 197                                 p->cred = cred;
 198                         }
 199                         break;
 200                 default:
 201                         goto error;
 202                 }
 203         }
 204
 205         if (p->fp && !p->fp->count)
 206         {
 207                 kfree(p->fp);
 208                 p->fp = NULL;
 209         }
 210         return 0;
 211
 212 error:
 213         scm_destroy(p);
 214         return err;
 215 }
 216 EXPORT_SYMBOL(__scm_send);
 217
 218 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 219 {
 220         struct cmsghdr __user *cm
 221                 = (__force struct cmsghdr __user *)msg->msg_control;
 222         struct cmsghdr cmhdr;
 223         int cmlen = CMSG_LEN(len);
 224         int err;
 225
 226         if (MSG_CMSG_COMPAT & msg->msg_flags)
 227                 return put_cmsg_compat(msg, level, type, len, data);
 228
 229         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 230                 msg->msg_flags |= MSG_CTRUNC;
 231                 return 0; /* XXX: return error? check spec. */
 232         }
 233         if (msg->msg_controllen < cmlen) {
 234                 msg->msg_flags |= MSG_CTRUNC;
 235                 cmlen = msg->msg_controllen;
 236         }
 237         cmhdr.cmsg_level = level;
 238         cmhdr.cmsg_type = type;
 239         cmhdr.cmsg_len = cmlen;
 240
 241         err = -EFAULT;
 242         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 243                 goto out;
 244         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 245                 goto out;
 246         cmlen = CMSG_SPACE(len);
 247         if (msg->msg_controllen < cmlen)
 248                 cmlen = msg->msg_controllen;
 249         msg->msg_control += cmlen;
 250         msg->msg_controllen -= cmlen;
 251         err = 0;
 252 out:
 253         return err;
 254 }
 255 EXPORT_SYMBOL(put_cmsg);
 256
 257 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 258 {
 259         struct cmsghdr __user *cm
 260                 = (__force struct cmsghdr __user*)msg->msg_control;
 261
 262         int fdmax = 0;
 263         int fdnum = scm->fp->count;
 264         struct file **fp = scm->fp->fp;
 265         int __user *cmfptr;
 266         int err = 0, i;
 267
 268         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 269                 scm_detach_fds_compat(msg, scm);
 270                 return;
 271         }
 272
 273         if (msg->msg_controllen > sizeof(struct cmsghdr))
 274                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 275                          / sizeof(int));
 276
 277         if (fdnum < fdmax)
 278                 fdmax = fdnum;
 279
 280         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 281              i++, cmfptr++)
 282         {
 283                 int new_fd;
 284                 err = security_file_receive(fp[i]);
 285                 if (err)
 286                         break;
 287                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 288                                           ? O_CLOEXEC : 0);
 289                 if (err < 0)
 290                         break;
 291                 new_fd = err;
 292                 err = put_user(new_fd, cmfptr);
 293                 if (err) {
 294                         put_unused_fd(new_fd);
 295                         break;
 296                 }
 297                 /* Bump the usage count and install the file. */
 298                 get_file(fp[i]);
 299                 fd_install(new_fd, fp[i]);
 300         }
 301
 302         if (i > 0)
 303         {
 304                 int cmlen = CMSG_LEN(i*sizeof(int));
 305                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 306                 if (!err)
 307                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 308                 if (!err)
 309                         err = put_user(cmlen, &cm->cmsg_len);
 310                 if (!err) {
 311                         cmlen = CMSG_SPACE(i*sizeof(int));
 312                         msg->msg_control += cmlen;
 313                         msg->msg_controllen -= cmlen;
 314                 }
 315         }
 316         if (i < fdnum || (fdnum && fdmax <= 0))
 317                 msg->msg_flags |= MSG_CTRUNC;
 318
 319         /*
 320          * All of the files that fit in the message have had their
 321          * usage counts incremented, so we just free the list.
 322          */
 323         __scm_destroy(scm);
 324 }
 325 EXPORT_SYMBOL(scm_detach_fds);
 326
 327 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 328 {
 329         struct scm_fp_list *new_fpl;
 330         int i;
 331
 332         if (!fpl)
 333                 return NULL;
 334
 335         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 336                           GFP_KERNEL);
 337         if (new_fpl) {
 338                 for (i = 0; i < fpl->count; i++)
 339                         get_file(fpl->fp[i]);
 340                 new_fpl->max = new_fpl->count;
 341         }
 342         return new_fpl;
 343 }
 344 EXPORT_SYMBOL(scm_fp_dup);