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         }
  83         fpp = &fpl->fp[fpl->count];
  84
  85         if (fpl->count + num > SCM_MAX_FD)
  86                 return -EINVAL;
  87
  88         /*
  89          *      Verify the descriptors and increment the usage count.
  90          */
  91
  92         for (i=0; i< num; i++)
  93         {
  94                 int fd = fdp[i];
  95                 struct file *file;
  96
  97                 if (fd < 0 || !(file = fget(fd)))
  98                         return -EBADF;
  99                 *fpp++ = file;
 100                 fpl->count++;
 101         }
 102         return num;
 103 }
 104
 105 void __scm_destroy(struct scm_cookie *scm)
 106 {
 107         struct scm_fp_list *fpl = scm->fp;
 108         int i;
 109
 110         if (fpl) {
 111                 scm->fp = NULL;
 112                 if (current->scm_work_list) {
 113                         list_add_tail(&fpl->list, current->scm_work_list);
 114                 } else {
 115                         LIST_HEAD(work_list);
 116
 117                         current->scm_work_list = &work_list;
 118
 119                         list_add(&fpl->list, &work_list);
 120                         while (!list_empty(&work_list)) {
 121                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 122
 123                                 list_del(&fpl->list);
 124                                 for (i=fpl->count-1; i>=0; i--)
 125                                         fput(fpl->fp[i]);
 126                                 kfree(fpl);
 127                         }
 128
 129                         current->scm_work_list = NULL;
 130                 }
 131         }
 132 }
 133
 134 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 135 {
 136         struct cmsghdr *cmsg;
 137         int err;
 138
 139         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 140         {
 141                 err = -EINVAL;
 142
 143                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 144                 /* The first check was omitted in <= 2.2.5. The reasoning was
 145                    that parser checks cmsg_len in any case, so that
 146                    additional check would be work duplication.
 147                    But if cmsg_level is not SOL_SOCKET, we do not check
 148                    for too short ancillary data object at all! Oops.
 149                    OK, let's add it...
 150                  */
 151                 if (!CMSG_OK(msg, cmsg))
 152                         goto error;
 153
 154                 if (cmsg->cmsg_level != SOL_SOCKET)
 155                         continue;
 156
 157                 switch (cmsg->cmsg_type)
 158                 {
 159                 case SCM_RIGHTS:
 160                         if (!sock->ops || sock->ops->family != PF_UNIX)
 161                                 goto error;
 162                         err=scm_fp_copy(cmsg, &p->fp);
 163                         if (err<0)
 164                                 goto error;
 165                         break;
 166                 case SCM_CREDENTIALS:
 167                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 168                                 goto error;
 169                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 170                         err = scm_check_creds(&p->creds);
 171                         if (err)
 172                                 goto error;
 173                         break;
 174                 default:
 175                         goto error;
 176                 }
 177         }
 178
 179         if (p->fp && !p->fp->count)
 180         {
 181                 kfree(p->fp);
 182                 p->fp = NULL;
 183         }
 184         return 0;
 185
 186 error:
 187         scm_destroy(p);
 188         return err;
 189 }
 190
 191 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 192 {
 193         struct cmsghdr __user *cm
 194                 = (__force struct cmsghdr __user *)msg->msg_control;
 195         struct cmsghdr cmhdr;
 196         int cmlen = CMSG_LEN(len);
 197         int err;
 198
 199         if (MSG_CMSG_COMPAT & msg->msg_flags)
 200                 return put_cmsg_compat(msg, level, type, len, data);
 201
 202         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 203                 msg->msg_flags |= MSG_CTRUNC;
 204                 return 0; /* XXX: return error? check spec. */
 205         }
 206         if (msg->msg_controllen < cmlen) {
 207                 msg->msg_flags |= MSG_CTRUNC;
 208                 cmlen = msg->msg_controllen;
 209         }
 210         cmhdr.cmsg_level = level;
 211         cmhdr.cmsg_type = type;
 212         cmhdr.cmsg_len = cmlen;
 213
 214         err = -EFAULT;
 215         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 216                 goto out;
 217         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 218                 goto out;
 219         cmlen = CMSG_SPACE(len);
 220         if (msg->msg_controllen < cmlen)
 221                 cmlen = msg->msg_controllen;
 222         msg->msg_control += cmlen;
 223         msg->msg_controllen -= cmlen;
 224         err = 0;
 225 out:
 226         return err;
 227 }
 228
 229 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 230 {
 231         struct cmsghdr __user *cm
 232                 = (__force struct cmsghdr __user*)msg->msg_control;
 233
 234         int fdmax = 0;
 235         int fdnum = scm->fp->count;
 236         struct file **fp = scm->fp->fp;
 237         int __user *cmfptr;
 238         int err = 0, i;
 239
 240         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 241                 scm_detach_fds_compat(msg, scm);
 242                 return;
 243         }
 244
 245         if (msg->msg_controllen > sizeof(struct cmsghdr))
 246                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 247                          / sizeof(int));
 248
 249         if (fdnum < fdmax)
 250                 fdmax = fdnum;
 251
 252         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 253              i++, cmfptr++)
 254         {
 255                 int new_fd;
 256                 err = security_file_receive(fp[i]);
 257                 if (err)
 258                         break;
 259                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 260                                           ? O_CLOEXEC : 0);
 261                 if (err < 0)
 262                         break;
 263                 new_fd = err;
 264                 err = put_user(new_fd, cmfptr);
 265                 if (err) {
 266                         put_unused_fd(new_fd);
 267                         break;
 268                 }
 269                 /* Bump the usage count and install the file. */
 270                 get_file(fp[i]);
 271                 fd_install(new_fd, fp[i]);
 272         }
 273
 274         if (i > 0)
 275         {
 276                 int cmlen = CMSG_LEN(i*sizeof(int));
 277                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 278                 if (!err)
 279                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 280                 if (!err)
 281                         err = put_user(cmlen, &cm->cmsg_len);
 282                 if (!err) {
 283                         cmlen = CMSG_SPACE(i*sizeof(int));
 284                         msg->msg_control += cmlen;
 285                         msg->msg_controllen -= cmlen;
 286                 }
 287         }
 288         if (i < fdnum || (fdnum && fdmax <= 0))
 289                 msg->msg_flags |= MSG_CTRUNC;
 290
 291         /*
 292          * All of the files that fit in the message have had their
 293          * usage counts incremented, so we just free the list.
 294          */
 295         __scm_destroy(scm);
 296 }
 297
 298 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 299 {
 300         struct scm_fp_list *new_fpl;
 301         int i;
 302
 303         if (!fpl)
 304                 return NULL;
 305
 306         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 307         if (new_fpl) {
 308                 for (i=fpl->count-1; i>=0; i--)
 309                         get_file(fpl->fp[i]);
 310                 memcpy(new_fpl, fpl, sizeof(*fpl));
 311         }
 312         return new_fpl;
 313 }
 314
 315 EXPORT_SYMBOL(__scm_destroy);
 316 EXPORT_SYMBOL(__scm_send);
 317 EXPORT_SYMBOL(put_cmsg);
 318 EXPORT_SYMBOL(scm_detach_fds);
 319 EXPORT_SYMBOL(scm_fp_dup);