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/signal.h>
  13 #include <linux/errno.h>
  14 #include <linux/sched.h>
  15 #include <linux/mm.h>
  16 #include <linux/kernel.h>
  17 #include <linux/major.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
  26 #include <asm/system.h>
  27 #include <asm/uaccess.h>
  28
  29 #include <linux/inet.h>
  30 #include <linux/netdevice.h>
  31 #include <net/ip.h>
  32 #include <net/protocol.h>
  33 #include <net/rarp.h>
  34 #include <net/tcp.h>
  35 #include <net/udp.h>
  36 #include <linux/skbuff.h>
  37 #include <net/sock.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         if ((creds->pid == current->pid || capable(CAP_SYS_ADMIN)) &&
  49             ((creds->uid == current->uid || creds->uid == current->euid ||
  50               creds->uid == current->suid) || capable(CAP_SETUID)) &&
  51             ((creds->gid == current->gid || creds->gid == current->egid ||
  52               creds->gid == current->sgid) || capable(CAP_SETGID))) {
  53                return 0;
  54         }
  55         return -EPERM;
  56 }
  57
  58 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  59 {
  60         int *fdp = (int*)CMSG_DATA(cmsg);
  61         struct scm_fp_list *fpl = *fplp;
  62         struct file **fpp;
  63         int i, num;
  64
  65         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  66
  67         if (num <= 0)
  68                 return 0;
  69
  70         if (num > SCM_MAX_FD)
  71                 return -EINVAL;
  72
  73         if (!fpl)
  74         {
  75                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  76                 if (!fpl)
  77                         return -ENOMEM;
  78                 *fplp = fpl;
  79                 fpl->count = 0;
  80         }
  81         fpp = &fpl->fp[fpl->count];
  82
  83         if (fpl->count + num > SCM_MAX_FD)
  84                 return -EINVAL;
  85
  86         /*
  87          *      Verify the descriptors and increment the usage count.
  88          */
  89
  90         for (i=0; i< num; i++)
  91         {
  92                 int fd = fdp[i];
  93                 struct file *file;
  94
  95                 if (fd < 0 || !(file = fget(fd)))
  96                         return -EBADF;
  97                 *fpp++ = file;
  98                 fpl->count++;
  99         }
 100         return num;
 101 }
 102
 103 void __scm_destroy(struct scm_cookie *scm)
 104 {
 105         struct scm_fp_list *fpl = scm->fp;
 106         int i;
 107
 108         if (fpl) {
 109                 scm->fp = NULL;
 110                 for (i=fpl->count-1; i>=0; i--)
 111                         fput(fpl->fp[i]);
 112                 kfree(fpl);
 113         }
 114 }
 115
 116 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 117 {
 118         struct cmsghdr *cmsg;
 119         int err;
 120
 121         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 122         {
 123                 err = -EINVAL;
 124
 125                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 126                 if ((unsigned long)(((char*)cmsg - (char*)msg->msg_control)
 127                                     + cmsg->cmsg_len) > msg->msg_controllen)
 128                         goto error;
 129
 130                 if (cmsg->cmsg_level != SOL_SOCKET)
 131                         continue;
 132
 133                 switch (cmsg->cmsg_type)
 134                 {
 135                 case SCM_RIGHTS:
 136                         err=scm_fp_copy(cmsg, &p->fp);
 137                         if (err<0)
 138                                 goto error;
 139                         break;
 140                 case SCM_CREDENTIALS:
 141                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 142                                 goto error;
 143                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 144                         err = scm_check_creds(&p->creds);
 145                         if (err)
 146                                 goto error;
 147                         break;
 148                 default:
 149                         goto error;
 150                 }
 151         }
 152
 153         if (p->fp && !p->fp->count)
 154         {
 155                 kfree(p->fp);
 156                 p->fp = NULL;
 157         }
 158
 159         err = -EINVAL;
 160         if (msg->msg_flags & MSG_CTLFLAGS)
 161                 goto error;
 162
 163         return 0;
 164
 165 error:
 166         scm_destroy(p);
 167         return err;
 168 }
 169
 170 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 171 {
 172         struct cmsghdr *cm = (struct cmsghdr*)msg->msg_control;
 173         struct cmsghdr cmhdr;
 174         int cmlen = CMSG_LEN(len);
 175         int err;
 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 *cm = (struct cmsghdr*)msg->msg_control;
 205
 206         int fdmax = (msg->msg_controllen - sizeof(struct cmsghdr))/sizeof(int);
 207         int fdnum = scm->fp->count;
 208         struct file **fp = scm->fp->fp;
 209         int *cmfptr;
 210         int err = 0, i;
 211
 212         if (fdnum < fdmax)
 213                 fdmax = fdnum;
 214
 215         for (i=0, cmfptr=(int*)CMSG_DATA(cm); i<fdmax; i++, cmfptr++)
 216         {
 217                 int new_fd;
 218                 err = get_unused_fd();
 219                 if (err < 0)
 220                         break;
 221                 new_fd = err;
 222                 err = put_user(new_fd, cmfptr);
 223                 if (err) {
 224                         put_unused_fd(new_fd);
 225                         break;
 226                 }
 227                 /* Bump the usage count and install the file. */
 228                 fp[i]->f_count++;
 229                 current->files->fd[new_fd] = fp[i];
 230         }
 231
 232         if (i > 0)
 233         {
 234                 int cmlen = CMSG_LEN(i*sizeof(int));
 235                 if (!err)
 236                         err = put_user(SOL_SOCKET, &cm->cmsg_level);
 237                 if (!err)
 238                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 239                 if (!err)
 240                         err = put_user(cmlen, &cm->cmsg_len);
 241                 if (!err) {
 242                         cmlen = CMSG_SPACE(i*sizeof(int));
 243                         msg->msg_control += cmlen;
 244                         msg->msg_controllen -= cmlen;
 245                 }
 246         }
 247         if (i < fdnum)
 248                 msg->msg_flags |= MSG_CTRUNC;
 249
 250         /*
 251          * All of the files that fit in the message have had their
 252          * usage counts incremented, so we just free the list.
 253          */
 254         __scm_destroy(scm);
 255 }
 256
 257 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 258 {
 259         struct scm_fp_list *new_fpl;
 260         int i;
 261
 262         if (!fpl)
 263                 return NULL;
 264
 265         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 266         if (new_fpl) {
 267                 memcpy(new_fpl, fpl, sizeof(*fpl));
 268
 269                 for (i=fpl->count-1; i>=0; i--)
 270                         fpl->fp[i]->f_count++;
 271         }
 272         return new_fpl;
 273 }