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