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                 INIT_LIST_HEAD(&fpl->list);
  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                 if (current->scm_work_list) {
 111                         list_add_tail(&fpl->list, current->scm_work_list);
 112                 } else {
 113                         LIST_HEAD(work_list);
 114
 115                         current->scm_work_list = &work_list;
 116
 117                         list_add(&fpl->list, &work_list);
 118                         while (!list_empty(&work_list)) {
 119                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 120
 121                                 list_del(&fpl->list);
 122                                 for (i=fpl->count-1; i>=0; i--)
 123                                         fput(fpl->fp[i]);
 124                                 kfree(fpl);
 125                         }
 126
 127                         current->scm_work_list = NULL;
 128                 }
 129         }
 130 }
 131
 132 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 133 {
 134         struct cmsghdr *cmsg;
 135         int err;
 136
 137         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 138         {
 139                 err = -EINVAL;
 140
 141                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 142                 /* The first check was omitted in <= 2.2.5. The reasoning was
 143                    that parser checks cmsg_len in any case, so that
 144                    additional check would be work duplication.
 145                    But if cmsg_level is not SOL_SOCKET, we do not check
 146                    for too short ancillary data object at all! Oops.
 147                    OK, let's add it...
 148                  */
 149                 if (!CMSG_OK(msg, cmsg))
 150                         goto error;
 151
 152                 if (cmsg->cmsg_level != SOL_SOCKET)
 153                         continue;
 154
 155                 switch (cmsg->cmsg_type)
 156                 {
 157                 case SCM_RIGHTS:
 158                         err=scm_fp_copy(cmsg, &p->fp);
 159                         if (err<0)
 160                                 goto error;
 161                         break;
 162                 case SCM_CREDENTIALS:
 163                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 164                                 goto error;
 165                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 166                         err = scm_check_creds(&p->creds);
 167                         if (err)
 168                                 goto error;
 169                         break;
 170                 default:
 171                         goto error;
 172                 }
 173         }
 174
 175         if (p->fp && !p->fp->count)
 176         {
 177                 kfree(p->fp);
 178                 p->fp = NULL;
 179         }
 180         return 0;
 181
 182 error:
 183         scm_destroy(p);
 184         return err;
 185 }
 186
 187 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 188 {
 189         struct cmsghdr __user *cm
 190                 = (__force struct cmsghdr __user *)msg->msg_control;
 191         struct cmsghdr cmhdr;
 192         int cmlen = CMSG_LEN(len);
 193         int err;
 194
 195         if (MSG_CMSG_COMPAT & msg->msg_flags)
 196                 return put_cmsg_compat(msg, level, type, len, data);
 197
 198         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 199                 msg->msg_flags |= MSG_CTRUNC;
 200                 return 0; /* XXX: return error? check spec. */
 201         }
 202         if (msg->msg_controllen < cmlen) {
 203                 msg->msg_flags |= MSG_CTRUNC;
 204                 cmlen = msg->msg_controllen;
 205         }
 206         cmhdr.cmsg_level = level;
 207         cmhdr.cmsg_type = type;
 208         cmhdr.cmsg_len = cmlen;
 209
 210         err = -EFAULT;
 211         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 212                 goto out;
 213         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 214                 goto out;
 215         cmlen = CMSG_SPACE(len);
 216         if (msg->msg_controllen < cmlen)
 217                 cmlen = msg->msg_controllen;
 218         msg->msg_control += cmlen;
 219         msg->msg_controllen -= cmlen;
 220         err = 0;
 221 out:
 222         return err;
 223 }
 224
 225 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 226 {
 227         struct cmsghdr __user *cm
 228                 = (__force struct cmsghdr __user*)msg->msg_control;
 229
 230         int fdmax = 0;
 231         int fdnum = scm->fp->count;
 232         struct file **fp = scm->fp->fp;
 233         int __user *cmfptr;
 234         int err = 0, i;
 235
 236         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 237                 scm_detach_fds_compat(msg, scm);
 238                 return;
 239         }
 240
 241         if (msg->msg_controllen > sizeof(struct cmsghdr))
 242                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 243                          / sizeof(int));
 244
 245         if (fdnum < fdmax)
 246                 fdmax = fdnum;
 247
 248         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 249              i++, cmfptr++)
 250         {
 251                 int new_fd;
 252                 err = security_file_receive(fp[i]);
 253                 if (err)
 254                         break;
 255                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 256                                           ? O_CLOEXEC : 0);
 257                 if (err < 0)
 258                         break;
 259                 new_fd = err;
 260                 err = put_user(new_fd, cmfptr);
 261                 if (err) {
 262                         put_unused_fd(new_fd);
 263                         break;
 264                 }
 265                 /* Bump the usage count and install the file. */
 266                 get_file(fp[i]);
 267                 fd_install(new_fd, fp[i]);
 268         }
 269
 270         if (i > 0)
 271         {
 272                 int cmlen = CMSG_LEN(i*sizeof(int));
 273                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 274                 if (!err)
 275                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 276                 if (!err)
 277                         err = put_user(cmlen, &cm->cmsg_len);
 278                 if (!err) {
 279                         cmlen = CMSG_SPACE(i*sizeof(int));
 280                         msg->msg_control += cmlen;
 281                         msg->msg_controllen -= cmlen;
 282                 }
 283         }
 284         if (i < fdnum || (fdnum && fdmax <= 0))
 285                 msg->msg_flags |= MSG_CTRUNC;
 286
 287         /*
 288          * All of the files that fit in the message have had their
 289          * usage counts incremented, so we just free the list.
 290          */
 291         __scm_destroy(scm);
 292 }
 293
 294 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 295 {
 296         struct scm_fp_list *new_fpl;
 297         int i;
 298
 299         if (!fpl)
 300                 return NULL;
 301
 302         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 303         if (new_fpl) {
 304                 INIT_LIST_HEAD(&new_fpl->list);
 305                 for (i=fpl->count-1; i>=0; i--)
 306                         get_file(fpl->fp[i]);
 307                 memcpy(new_fpl, fpl, sizeof(*fpl));
 308         }
 309         return new_fpl;
 310 }
 311
 312 EXPORT_SYMBOL(__scm_destroy);
 313 EXPORT_SYMBOL(__scm_send);
 314 EXPORT_SYMBOL(put_cmsg);
 315 EXPORT_SYMBOL(scm_detach_fds);
 316 EXPORT_SYMBOL(scm_fp_dup);