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/errno.h>
  15 #include <linux/sched.h>
  16 #include <linux/mm.h>
  17 #include <linux/kernel.h>
  18 #include <linux/stat.h>
  19 #include <linux/socket.h>
  20 #include <linux/file.h>
  21 #include <linux/fcntl.h>
  22 #include <linux/net.h>
  23 #include <linux/interrupt.h>
  24 #include <linux/netdevice.h>
  25 #include <linux/security.h>
  26
  27 #include <asm/system.h>
  28 #include <asm/uaccess.h>
  29
  30 #include <net/protocol.h>
  31 #include <linux/skbuff.h>
  32 #include <net/sock.h>
  33 #include <net/compat.h>
  34 #include <net/scm.h>
  35
  36
  37 /*
  38  *      Only allow a user to send credentials, that they could set with
  39  *      setu(g)id.
  40  */
  41
  42 static __inline__ int scm_check_creds(struct ucred *creds)
  43 {
  44         if ((creds->pid == current->tgid || capable(CAP_SYS_ADMIN)) &&
  45             ((creds->uid == current->uid || creds->uid == current->euid ||
  46               creds->uid == current->suid) || capable(CAP_SETUID)) &&
  47             ((creds->gid == current->gid || creds->gid == current->egid ||
  48               creds->gid == current->sgid) || capable(CAP_SETGID))) {
  49                return 0;
  50         }
  51         return -EPERM;
  52 }
  53
  54 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  55 {
  56         int *fdp = (int*)CMSG_DATA(cmsg);
  57         struct scm_fp_list *fpl = *fplp;
  58         struct file **fpp;
  59         int i, num;
  60
  61         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  62
  63         if (num <= 0)
  64                 return 0;
  65
  66         if (num > SCM_MAX_FD)
  67                 return -EINVAL;
  68
  69         if (!fpl)
  70         {
  71                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  72                 if (!fpl)
  73                         return -ENOMEM;
  74                 *fplp = fpl;
  75                 fpl->count = 0;
  76         }
  77         fpp = &fpl->fp[fpl->count];
  78
  79         if (fpl->count + num > SCM_MAX_FD)
  80                 return -EINVAL;
  81
  82         /*
  83          *      Verify the descriptors and increment the usage count.
  84          */
  85
  86         for (i=0; i< num; i++)
  87         {
  88                 int fd = fdp[i];
  89                 struct file *file;
  90
  91                 if (fd < 0 || !(file = fget(fd)))
  92                         return -EBADF;
  93                 *fpp++ = file;
  94                 fpl->count++;
  95         }
  96         return num;
  97 }
  98
  99 void __scm_destroy(struct scm_cookie *scm)
 100 {
 101         struct scm_fp_list *fpl = scm->fp;
 102         int i;
 103
 104         if (fpl) {
 105                 scm->fp = NULL;
 106                 for (i=fpl->count-1; i>=0; i--)
 107                         fput(fpl->fp[i]);
 108                 kfree(fpl);
 109         }
 110 }
 111
 112 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 113 {
 114         struct cmsghdr *cmsg;
 115         int err;
 116
 117         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 118         {
 119                 err = -EINVAL;
 120
 121                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 122                 /* The first check was omitted in <= 2.2.5. The reasoning was
 123                    that parser checks cmsg_len in any case, so that
 124                    additional check would be work duplication.
 125                    But if cmsg_level is not SOL_SOCKET, we do not check
 126                    for too short ancillary data object at all! Oops.
 127                    OK, let's add it...
 128                  */
 129                 if (!CMSG_OK(msg, cmsg))
 130                         goto error;
 131
 132                 if (cmsg->cmsg_level != SOL_SOCKET)
 133                         continue;
 134
 135                 switch (cmsg->cmsg_type)
 136                 {
 137                 case SCM_RIGHTS:
 138                         err=scm_fp_copy(cmsg, &p->fp);
 139                         if (err<0)
 140                                 goto error;
 141                         break;
 142                 case SCM_CREDENTIALS:
 143                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 144                                 goto error;
 145                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 146                         err = scm_check_creds(&p->creds);
 147                         if (err)
 148                                 goto error;
 149                         break;
 150                 default:
 151                         goto error;
 152                 }
 153         }
 154
 155         if (p->fp && !p->fp->count)
 156         {
 157                 kfree(p->fp);
 158                 p->fp = NULL;
 159         }
 160         return 0;
 161
 162 error:
 163         scm_destroy(p);
 164         return err;
 165 }
 166
 167 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 168 {
 169         struct cmsghdr __user *cm = (struct cmsghdr __user *)msg->msg_control;
 170         struct cmsghdr cmhdr;
 171         int cmlen = CMSG_LEN(len);
 172         int err;
 173
 174         if (MSG_CMSG_COMPAT & msg->msg_flags)
 175                 return put_cmsg_compat(msg, level, type, len, data);
 176
 177         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 178                 msg->msg_flags |= MSG_CTRUNC;
 179                 return 0; /* XXX: return error? check spec. */
 180         }
 181         if (msg->msg_controllen < cmlen) {
 182                 msg->msg_flags |= MSG_CTRUNC;
 183                 cmlen = msg->msg_controllen;
 184         }
 185         cmhdr.cmsg_level = level;
 186         cmhdr.cmsg_type = type;
 187         cmhdr.cmsg_len = cmlen;
 188
 189         err = -EFAULT;
 190         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 191                 goto out;
 192         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 193                 goto out;
 194         cmlen = CMSG_SPACE(len);
 195         msg->msg_control += cmlen;
 196         msg->msg_controllen -= cmlen;
 197         err = 0;
 198 out:
 199         return err;
 200 }
 201
 202 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 203 {
 204         struct cmsghdr __user *cm = (struct cmsghdr __user*)msg->msg_control;
 205
 206         int fdmax = 0;
 207         int fdnum = scm->fp->count;
 208         struct file **fp = scm->fp->fp;
 209         int __user *cmfptr;
 210         int err = 0, i;
 211
 212         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 213                 scm_detach_fds_compat(msg, scm);
 214                 return;
 215         }
 216
 217         if (msg->msg_controllen > sizeof(struct cmsghdr))
 218                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 219                          / sizeof(int));
 220
 221         if (fdnum < fdmax)
 222                 fdmax = fdnum;
 223
 224         for (i=0, cmfptr=(int __user *)CMSG_DATA(cm); i<fdmax; i++, cmfptr++)
 225         {
 226                 int new_fd;
 227                 err = security_file_receive(fp[i]);
 228                 if (err)
 229                         break;
 230                 err = get_unused_fd();
 231                 if (err < 0)
 232                         break;
 233                 new_fd = err;
 234                 err = put_user(new_fd, cmfptr);
 235                 if (err) {
 236                         put_unused_fd(new_fd);
 237                         break;
 238                 }
 239                 /* Bump the usage count and install the file. */
 240                 get_file(fp[i]);
 241                 fd_install(new_fd, fp[i]);
 242         }
 243
 244         if (i > 0)
 245         {
 246                 int cmlen = CMSG_LEN(i*sizeof(int));
 247                 if (!err)
 248                         err = put_user(SOL_SOCKET, &cm->cmsg_level);
 249                 if (!err)
 250                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 251                 if (!err)
 252                         err = put_user(cmlen, &cm->cmsg_len);
 253                 if (!err) {
 254                         cmlen = CMSG_SPACE(i*sizeof(int));
 255                         msg->msg_control += cmlen;
 256                         msg->msg_controllen -= cmlen;
 257                 }
 258         }
 259         if (i < fdnum || (fdnum && fdmax <= 0))
 260                 msg->msg_flags |= MSG_CTRUNC;
 261
 262         /*
 263          * All of the files that fit in the message have had their
 264          * usage counts incremented, so we just free the list.
 265          */
 266         __scm_destroy(scm);
 267 }
 268
 269 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 270 {
 271         struct scm_fp_list *new_fpl;
 272         int i;
 273
 274         if (!fpl)
 275                 return NULL;
 276
 277         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 278         if (new_fpl) {
 279                 for (i=fpl->count-1; i>=0; i--)
 280                         get_file(fpl->fp[i]);
 281                 memcpy(new_fpl, fpl, sizeof(*fpl));
 282         }
 283         return new_fpl;
 284 }
 285
 286 EXPORT_SYMBOL(__scm_destroy);
 287 EXPORT_SYMBOL(__scm_send);
 288 EXPORT_SYMBOL(put_cmsg);
 289 EXPORT_SYMBOL(scm_detach_fds);
 290 EXPORT_SYMBOL(scm_fp_dup);