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
  30 #include <asm/system.h>
  31 #include <asm/uaccess.h>
  32
  33 #include <net/protocol.h>
  34 #include <linux/skbuff.h>
  35 #include <net/sock.h>
  36 #include <net/compat.h>
  37 #include <net/scm.h>
  38
  39
  40 /*
  41  *      Only allow a user to send credentials, that they could set with
  42  *      setu(g)id.
  43  */
  44
  45 static __inline__ int scm_check_creds(struct ucred *creds)
  46 {
  47         if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
  48             ((creds->uid == current->uid || creds->uid == current->euid ||
  49               creds->uid == current->suid) || capable(CAP_SETUID)) &&
  50             ((creds->gid == current->gid || creds->gid == current->egid ||
  51               creds->gid == current->sgid) || capable(CAP_SETGID))) {
  52                return 0;
  53         }
  54         return -EPERM;
  55 }
  56
  57 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  58 {
  59         int *fdp = (int*)CMSG_DATA(cmsg);
  60         struct scm_fp_list *fpl = *fplp;
  61         struct file **fpp;
  62         int i, num;
  63
  64         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  65
  66         if (num <= 0)
  67                 return 0;
  68
  69         if (num > SCM_MAX_FD)
  70                 return -EINVAL;
  71
  72         if (!fpl)
  73         {
  74                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  75                 if (!fpl)
  76                         return -ENOMEM;
  77                 *fplp = fpl;
  78                 fpl->count = 0;
  79         }
  80         fpp = &fpl->fp[fpl->count];
  81
  82         if (fpl->count + num > SCM_MAX_FD)
  83                 return -EINVAL;
  84
  85         /*
  86          *      Verify the descriptors and increment the usage count.
  87          */
  88
  89         for (i=0; i< num; i++)
  90         {
  91                 int fd = fdp[i];
  92                 struct file *file;
  93
  94                 if (fd < 0 || !(file = fget(fd)))
  95                         return -EBADF;
  96                 *fpp++ = file;
  97                 fpl->count++;
  98         }
  99         return num;
 100 }
 101
 102 void __scm_destroy(struct scm_cookie *scm)
 103 {
 104         struct scm_fp_list *fpl = scm->fp;
 105         int i;
 106
 107         if (fpl) {
 108                 scm->fp = NULL;
 109                 if (current->scm_work_list) {
 110                         list_add_tail(&fpl->list, current->scm_work_list);
 111                 } else {
 112                         LIST_HEAD(work_list);
 113
 114                         current->scm_work_list = &work_list;
 115
 116                         list_add(&fpl->list, &work_list);
 117                         while (!list_empty(&work_list)) {
 118                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 119
 120                                 list_del(&fpl->list);
 121                                 for (i=fpl->count-1; i>=0; i--)
 122                                         fput(fpl->fp[i]);
 123                                 kfree(fpl);
 124                         }
 125
 126                         current->scm_work_list = NULL;
 127                 }
 128         }
 129 }
 130
 131 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 132 {
 133         struct cmsghdr *cmsg;
 134         int err;
 135
 136         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 137         {
 138                 err = -EINVAL;
 139
 140                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 141                 /* The first check was omitted in <= 2.2.5. The reasoning was
 142                    that parser checks cmsg_len in any case, so that
 143                    additional check would be work duplication.
 144                    But if cmsg_level is not SOL_SOCKET, we do not check
 145                    for too short ancillary data object at all! Oops.
 146                    OK, let's add it...
 147                  */
 148                 if (!CMSG_OK(msg, cmsg))
 149                         goto error;
 150
 151                 if (cmsg->cmsg_level != SOL_SOCKET)
 152                         continue;
 153
 154                 switch (cmsg->cmsg_type)
 155                 {
 156                 case SCM_RIGHTS:
 157                         err=scm_fp_copy(cmsg, &p->fp);
 158                         if (err<0)
 159                                 goto error;
 160                         break;
 161                 case SCM_CREDENTIALS:
 162                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 163                                 goto error;
 164                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 165                         err = scm_check_creds(&p->creds);
 166                         if (err)
 167                                 goto error;
 168                         break;
 169                 default:
 170                         goto error;
 171                 }
 172         }
 173
 174         if (p->fp && !p->fp->count)
 175         {
 176                 kfree(p->fp);
 177                 p->fp = NULL;
 178         }
 179         return 0;
 180
 181 error:
 182         scm_destroy(p);
 183         return err;
 184 }
 185
 186 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 187 {
 188         struct cmsghdr __user *cm
 189                 = (__force struct cmsghdr __user *)msg->msg_control;
 190         struct cmsghdr cmhdr;
 191         int cmlen = CMSG_LEN(len);
 192         int err;
 193
 194         if (MSG_CMSG_COMPAT & msg->msg_flags)
 195                 return put_cmsg_compat(msg, level, type, len, data);
 196
 197         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 198                 msg->msg_flags |= MSG_CTRUNC;
 199                 return 0; /* XXX: return error? check spec. */
 200         }
 201         if (msg->msg_controllen < cmlen) {
 202                 msg->msg_flags |= MSG_CTRUNC;
 203                 cmlen = msg->msg_controllen;
 204         }
 205         cmhdr.cmsg_level = level;
 206         cmhdr.cmsg_type = type;
 207         cmhdr.cmsg_len = cmlen;
 208
 209         err = -EFAULT;
 210         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 211                 goto out;
 212         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 213                 goto out;
 214         cmlen = CMSG_SPACE(len);
 215         if (msg->msg_controllen < cmlen)
 216                 cmlen = msg->msg_controllen;
 217         msg->msg_control += cmlen;
 218         msg->msg_controllen -= cmlen;
 219         err = 0;
 220 out:
 221         return err;
 222 }
 223
 224 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 225 {
 226         struct cmsghdr __user *cm
 227                 = (__force struct cmsghdr __user*)msg->msg_control;
 228
 229         int fdmax = 0;
 230         int fdnum = scm->fp->count;
 231         struct file **fp = scm->fp->fp;
 232         int __user *cmfptr;
 233         int err = 0, i;
 234
 235         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 236                 scm_detach_fds_compat(msg, scm);
 237                 return;
 238         }
 239
 240         if (msg->msg_controllen > sizeof(struct cmsghdr))
 241                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 242                          / sizeof(int));
 243
 244         if (fdnum < fdmax)
 245                 fdmax = fdnum;
 246
 247         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 248              i++, cmfptr++)
 249         {
 250                 int new_fd;
 251                 err = security_file_receive(fp[i]);
 252                 if (err)
 253                         break;
 254                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 255                                           ? O_CLOEXEC : 0);
 256                 if (err < 0)
 257                         break;
 258                 new_fd = err;
 259                 err = put_user(new_fd, cmfptr);
 260                 if (err) {
 261                         put_unused_fd(new_fd);
 262                         break;
 263                 }
 264                 /* Bump the usage count and install the file. */
 265                 get_file(fp[i]);
 266                 fd_install(new_fd, fp[i]);
 267         }
 268
 269         if (i > 0)
 270         {
 271                 int cmlen = CMSG_LEN(i*sizeof(int));
 272                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 273                 if (!err)
 274                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 275                 if (!err)
 276                         err = put_user(cmlen, &cm->cmsg_len);
 277                 if (!err) {
 278                         cmlen = CMSG_SPACE(i*sizeof(int));
 279                         msg->msg_control += cmlen;
 280                         msg->msg_controllen -= cmlen;
 281                 }
 282         }
 283         if (i < fdnum || (fdnum && fdmax <= 0))
 284                 msg->msg_flags |= MSG_CTRUNC;
 285
 286         /*
 287          * All of the files that fit in the message have had their
 288          * usage counts incremented, so we just free the list.
 289          */
 290         __scm_destroy(scm);
 291 }
 292
 293 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 294 {
 295         struct scm_fp_list *new_fpl;
 296         int i;
 297
 298         if (!fpl)
 299                 return NULL;
 300
 301         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 302         if (new_fpl) {
 303                 for (i=fpl->count-1; i>=0; i--)
 304                         get_file(fpl->fp[i]);
 305                 memcpy(new_fpl, fpl, sizeof(*fpl));
 306         }
 307         return new_fpl;
 308 }
 309
 310 EXPORT_SYMBOL(__scm_destroy);
 311 EXPORT_SYMBOL(__scm_send);
 312 EXPORT_SYMBOL(put_cmsg);
 313 EXPORT_SYMBOL(scm_detach_fds);
 314 EXPORT_SYMBOL(scm_fp_dup);