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 #include <linux/slab.h>
  30
  31 #include <asm/system.h>
  32 #include <asm/uaccess.h>
  33
  34 #include <net/protocol.h>
  35 #include <linux/skbuff.h>
  36 #include <net/sock.h>
  37 #include <net/compat.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         const struct cred *cred = current_cred();
  49
  50         if ((creds->pid == task_tgid_vnr(current) || capable(CAP_SYS_ADMIN)) &&
  51             ((creds->uid == cred->uid   || creds->uid == cred->euid ||
  52               creds->uid == cred->suid) || capable(CAP_SETUID)) &&
  53             ((creds->gid == cred->gid   || creds->gid == cred->egid ||
  54               creds->gid == cred->sgid) || capable(CAP_SETGID))) {
  55                return 0;
  56         }
  57         return -EPERM;
  58 }
  59
  60 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  61 {
  62         int *fdp = (int*)CMSG_DATA(cmsg);
  63         struct scm_fp_list *fpl = *fplp;
  64         struct file **fpp;
  65         int i, num;
  66
  67         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  68
  69         if (num <= 0)
  70                 return 0;
  71
  72         if (num > SCM_MAX_FD)
  73                 return -EINVAL;
  74
  75         if (!fpl)
  76         {
  77                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  78                 if (!fpl)
  79                         return -ENOMEM;
  80                 *fplp = fpl;
  81                 fpl->count = 0;
  82         }
  83         fpp = &fpl->fp[fpl->count];
  84
  85         if (fpl->count + num > SCM_MAX_FD)
  86                 return -EINVAL;
  87
  88         /*
  89          *      Verify the descriptors and increment the usage count.
  90          */
  91
  92         for (i=0; i< num; i++)
  93         {
  94                 int fd = fdp[i];
  95                 struct file *file;
  96
  97                 if (fd < 0 || !(file = fget(fd)))
  98                         return -EBADF;
  99                 *fpp++ = file;
 100                 fpl->count++;
 101         }
 102         return num;
 103 }
 104
 105 void __scm_destroy(struct scm_cookie *scm)
 106 {
 107         struct scm_fp_list *fpl = scm->fp;
 108         int i;
 109
 110         if (fpl) {
 111                 scm->fp = NULL;
 112                 if (current->scm_work_list) {
 113                         list_add_tail(&fpl->list, current->scm_work_list);
 114                 } else {
 115                         LIST_HEAD(work_list);
 116
 117                         current->scm_work_list = &work_list;
 118
 119                         list_add(&fpl->list, &work_list);
 120                         while (!list_empty(&work_list)) {
 121                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 122
 123                                 list_del(&fpl->list);
 124                                 for (i=fpl->count-1; i>=0; i--)
 125                                         fput(fpl->fp[i]);
 126                                 kfree(fpl);
 127                         }
 128
 129                         current->scm_work_list = NULL;
 130                 }
 131         }
 132 }
 133 EXPORT_SYMBOL(__scm_destroy);
 134
 135 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 136 {
 137         struct cmsghdr *cmsg;
 138         int err;
 139
 140         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 141         {
 142                 err = -EINVAL;
 143
 144                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 145                 /* The first check was omitted in <= 2.2.5. The reasoning was
 146                    that parser checks cmsg_len in any case, so that
 147                    additional check would be work duplication.
 148                    But if cmsg_level is not SOL_SOCKET, we do not check
 149                    for too short ancillary data object at all! Oops.
 150                    OK, let's add it...
 151                  */
 152                 if (!CMSG_OK(msg, cmsg))
 153                         goto error;
 154
 155                 if (cmsg->cmsg_level != SOL_SOCKET)
 156                         continue;
 157
 158                 switch (cmsg->cmsg_type)
 159                 {
 160                 case SCM_RIGHTS:
 161                         if (!sock->ops || sock->ops->family != PF_UNIX)
 162                                 goto error;
 163                         err=scm_fp_copy(cmsg, &p->fp);
 164                         if (err<0)
 165                                 goto error;
 166                         break;
 167                 case SCM_CREDENTIALS:
 168                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 169                                 goto error;
 170                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 171                         err = scm_check_creds(&p->creds);
 172                         if (err)
 173                                 goto error;
 174
 175                         if (pid_vnr(p->pid) != p->creds.pid) {
 176                                 struct pid *pid;
 177                                 err = -ESRCH;
 178                                 pid = find_get_pid(p->creds.pid);
 179                                 if (!pid)
 180                                         goto error;
 181                                 put_pid(p->pid);
 182                                 p->pid = pid;
 183                         }
 184
 185                         if ((p->cred->euid != p->creds.uid) ||
 186                                 (p->cred->egid != p->creds.gid)) {
 187                                 struct cred *cred;
 188                                 err = -ENOMEM;
 189                                 cred = prepare_creds();
 190                                 if (!cred)
 191                                         goto error;
 192
 193                                 cred->uid = cred->euid = p->creds.uid;
 194                                 cred->gid = cred->egid = p->creds.uid;
 195                                 put_cred(p->cred);
 196                                 p->cred = cred;
 197                         }
 198                         break;
 199                 default:
 200                         goto error;
 201                 }
 202         }
 203
 204         if (p->fp && !p->fp->count)
 205         {
 206                 kfree(p->fp);
 207                 p->fp = NULL;
 208         }
 209         return 0;
 210
 211 error:
 212         scm_destroy(p);
 213         return err;
 214 }
 215 EXPORT_SYMBOL(__scm_send);
 216
 217 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 218 {
 219         struct cmsghdr __user *cm
 220                 = (__force struct cmsghdr __user *)msg->msg_control;
 221         struct cmsghdr cmhdr;
 222         int cmlen = CMSG_LEN(len);
 223         int err;
 224
 225         if (MSG_CMSG_COMPAT & msg->msg_flags)
 226                 return put_cmsg_compat(msg, level, type, len, data);
 227
 228         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 229                 msg->msg_flags |= MSG_CTRUNC;
 230                 return 0; /* XXX: return error? check spec. */
 231         }
 232         if (msg->msg_controllen < cmlen) {
 233                 msg->msg_flags |= MSG_CTRUNC;
 234                 cmlen = msg->msg_controllen;
 235         }
 236         cmhdr.cmsg_level = level;
 237         cmhdr.cmsg_type = type;
 238         cmhdr.cmsg_len = cmlen;
 239
 240         err = -EFAULT;
 241         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 242                 goto out;
 243         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 244                 goto out;
 245         cmlen = CMSG_SPACE(len);
 246         if (msg->msg_controllen < cmlen)
 247                 cmlen = msg->msg_controllen;
 248         msg->msg_control += cmlen;
 249         msg->msg_controllen -= cmlen;
 250         err = 0;
 251 out:
 252         return err;
 253 }
 254 EXPORT_SYMBOL(put_cmsg);
 255
 256 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 257 {
 258         struct cmsghdr __user *cm
 259                 = (__force struct cmsghdr __user*)msg->msg_control;
 260
 261         int fdmax = 0;
 262         int fdnum = scm->fp->count;
 263         struct file **fp = scm->fp->fp;
 264         int __user *cmfptr;
 265         int err = 0, i;
 266
 267         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 268                 scm_detach_fds_compat(msg, scm);
 269                 return;
 270         }
 271
 272         if (msg->msg_controllen > sizeof(struct cmsghdr))
 273                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 274                          / sizeof(int));
 275
 276         if (fdnum < fdmax)
 277                 fdmax = fdnum;
 278
 279         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 280              i++, cmfptr++)
 281         {
 282                 int new_fd;
 283                 err = security_file_receive(fp[i]);
 284                 if (err)
 285                         break;
 286                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 287                                           ? O_CLOEXEC : 0);
 288                 if (err < 0)
 289                         break;
 290                 new_fd = err;
 291                 err = put_user(new_fd, cmfptr);
 292                 if (err) {
 293                         put_unused_fd(new_fd);
 294                         break;
 295                 }
 296                 /* Bump the usage count and install the file. */
 297                 get_file(fp[i]);
 298                 fd_install(new_fd, fp[i]);
 299         }
 300
 301         if (i > 0)
 302         {
 303                 int cmlen = CMSG_LEN(i*sizeof(int));
 304                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 305                 if (!err)
 306                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 307                 if (!err)
 308                         err = put_user(cmlen, &cm->cmsg_len);
 309                 if (!err) {
 310                         cmlen = CMSG_SPACE(i*sizeof(int));
 311                         msg->msg_control += cmlen;
 312                         msg->msg_controllen -= cmlen;
 313                 }
 314         }
 315         if (i < fdnum || (fdnum && fdmax <= 0))
 316                 msg->msg_flags |= MSG_CTRUNC;
 317
 318         /*
 319          * All of the files that fit in the message have had their
 320          * usage counts incremented, so we just free the list.
 321          */
 322         __scm_destroy(scm);
 323 }
 324 EXPORT_SYMBOL(scm_detach_fds);
 325
 326 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 327 {
 328         struct scm_fp_list *new_fpl;
 329         int i;
 330
 331         if (!fpl)
 332                 return NULL;
 333
 334         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 335         if (new_fpl) {
 336                 for (i=fpl->count-1; i>=0; i--)
 337                         get_file(fpl->fp[i]);
 338                 memcpy(new_fpl, fpl, sizeof(*fpl));
 339         }
 340         return new_fpl;
 341 }
 342 EXPORT_SYMBOL(scm_fp_dup);