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