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/major.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->cmsg_len < sizeof(struct cmsghdr) ||
 131                     (unsigned long)(((char*)cmsg - (char*)msg->msg_control)
 132                                     + cmsg->cmsg_len) > msg->msg_controllen)
 133                         goto error;
 134
 135                 if (cmsg->cmsg_level != SOL_SOCKET)
 136                         continue;
 137
 138                 switch (cmsg->cmsg_type)
 139                 {
 140                 case SCM_RIGHTS:
 141                         err=scm_fp_copy(cmsg, &p->fp);
 142                         if (err<0)
 143                                 goto error;
 144                         break;
 145                 case SCM_CREDENTIALS:
 146                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 147                                 goto error;
 148                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 149                         err = scm_check_creds(&p->creds);
 150                         if (err)
 151                                 goto error;
 152                         break;
 153                 default:
 154                         goto error;
 155                 }
 156         }
 157
 158         if (p->fp && !p->fp->count)
 159         {
 160                 kfree(p->fp);
 161                 p->fp = NULL;
 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 __user *cm = (struct cmsghdr __user *)msg->msg_control;
 173         struct cmsghdr cmhdr;
 174         int cmlen = CMSG_LEN(len);
 175         int err;
 176
 177         if (MSG_CMSG_COMPAT & msg->msg_flags)
 178                 return put_cmsg_compat(msg, level, type, len, data);
 179
 180         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 181                 msg->msg_flags |= MSG_CTRUNC;
 182                 return 0; /* XXX: return error? check spec. */
 183         }
 184         if (msg->msg_controllen < cmlen) {
 185                 msg->msg_flags |= MSG_CTRUNC;
 186                 cmlen = msg->msg_controllen;
 187         }
 188         cmhdr.cmsg_level = level;
 189         cmhdr.cmsg_type = type;
 190         cmhdr.cmsg_len = cmlen;
 191
 192         err = -EFAULT;
 193         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 194                 goto out;
 195         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 196                 goto out;
 197         cmlen = CMSG_SPACE(len);
 198         msg->msg_control += cmlen;
 199         msg->msg_controllen -= cmlen;
 200         err = 0;
 201 out:
 202         return err;
 203 }
 204
 205 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 206 {
 207         struct cmsghdr __user *cm = (struct cmsghdr __user*)msg->msg_control;
 208
 209         int fdmax = 0;
 210         int fdnum = scm->fp->count;
 211         struct file **fp = scm->fp->fp;
 212         int __user *cmfptr;
 213         int err = 0, i;
 214
 215         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 216                 scm_detach_fds_compat(msg, scm);
 217                 return;
 218         }
 219
 220         if (msg->msg_controllen > sizeof(struct cmsghdr))
 221                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 222                          / sizeof(int));
 223
 224         if (fdnum < fdmax)
 225                 fdmax = fdnum;
 226
 227         for (i=0, cmfptr=(int __user *)CMSG_DATA(cm); i<fdmax; i++, cmfptr++)
 228         {
 229                 int new_fd;
 230                 err = security_file_receive(fp[i]);
 231                 if (err)
 232                         break;
 233                 err = get_unused_fd();
 234                 if (err < 0)
 235                         break;
 236                 new_fd = err;
 237                 err = put_user(new_fd, cmfptr);
 238                 if (err) {
 239                         put_unused_fd(new_fd);
 240                         break;
 241                 }
 242                 /* Bump the usage count and install the file. */
 243                 get_file(fp[i]);
 244                 fd_install(new_fd, fp[i]);
 245         }
 246
 247         if (i > 0)
 248         {
 249                 int cmlen = CMSG_LEN(i*sizeof(int));
 250                 if (!err)
 251                         err = put_user(SOL_SOCKET, &cm->cmsg_level);
 252                 if (!err)
 253                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 254                 if (!err)
 255                         err = put_user(cmlen, &cm->cmsg_len);
 256                 if (!err) {
 257                         cmlen = CMSG_SPACE(i*sizeof(int));
 258                         msg->msg_control += cmlen;
 259                         msg->msg_controllen -= cmlen;
 260                 }
 261         }
 262         if (i < fdnum || (fdnum && fdmax <= 0))
 263                 msg->msg_flags |= MSG_CTRUNC;
 264
 265         /*
 266          * All of the files that fit in the message have had their
 267          * usage counts incremented, so we just free the list.
 268          */
 269         __scm_destroy(scm);
 270 }
 271
 272 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 273 {
 274         struct scm_fp_list *new_fpl;
 275         int i;
 276
 277         if (!fpl)
 278                 return NULL;
 279
 280         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 281         if (new_fpl) {
 282                 for (i=fpl->count-1; i>=0; i--)
 283                         get_file(fpl->fp[i]);
 284                 memcpy(new_fpl, fpl, sizeof(*fpl));
 285         }
 286         return new_fpl;
 287 }
 288
 289 EXPORT_SYMBOL(__scm_destroy);
 290 EXPORT_SYMBOL(__scm_send);
 291 EXPORT_SYMBOL(put_cmsg);
 292 EXPORT_SYMBOL(scm_detach_fds);
 293 EXPORT_SYMBOL(scm_fp_dup);