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                 fpl->max = SCM_MAX_FD;
  83                 fpl->user = NULL;
  84         }
  85         fpp = &fpl->fp[fpl->count];
  86
  87         if (fpl->count + num > fpl->max)
  88                 return -EINVAL;
  89
  90         /*
  91          *      Verify the descriptors and increment the usage count.
  92          */
  93
  94         for (i=0; i< num; i++)
  95         {
  96                 int fd = fdp[i];
  97                 struct file *file;
  98
  99                 if (fd < 0 || !(file = fget_raw(fd)))
 100                         return -EBADF;
 101                 *fpp++ = file;
 102                 fpl->count++;
 103         }
 104
 105         if (!fpl->user)
 106                 fpl->user = get_uid(current_user());
 107
 108         return num;
 109 }
 110
 111 void __scm_destroy(struct scm_cookie *scm)
 112 {
 113         struct scm_fp_list *fpl = scm->fp;
 114         int i;
 115
 116         if (fpl) {
 117                 scm->fp = NULL;
 118                 if (current->scm_work_list) {
 119                         list_add_tail(&fpl->list, current->scm_work_list);
 120                 } else {
 121                         LIST_HEAD(work_list);
 122
 123                         current->scm_work_list = &work_list;
 124
 125                         list_add(&fpl->list, &work_list);
 126                         while (!list_empty(&work_list)) {
 127                                 fpl = list_first_entry(&work_list, struct scm_fp_list, list);
 128
 129                                 list_del(&fpl->list);
 130                                 for (i=fpl->count-1; i>=0; i--)
 131                                         fput(fpl->fp[i]);
 132                                 free_uid(fpl->user);
 133                                 kfree(fpl);
 134                         }
 135
 136                         current->scm_work_list = NULL;
 137                 }
 138         }
 139 }
 140 EXPORT_SYMBOL(__scm_destroy);
 141
 142 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 143 {
 144         struct cmsghdr *cmsg;
 145         int err;
 146
 147         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 148         {
 149                 err = -EINVAL;
 150
 151                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 152                 /* The first check was omitted in <= 2.2.5. The reasoning was
 153                    that parser checks cmsg_len in any case, so that
 154                    additional check would be work duplication.
 155                    But if cmsg_level is not SOL_SOCKET, we do not check
 156                    for too short ancillary data object at all! Oops.
 157                    OK, let's add it...
 158                  */
 159                 if (!CMSG_OK(msg, cmsg))
 160                         goto error;
 161
 162                 if (cmsg->cmsg_level != SOL_SOCKET)
 163                         continue;
 164
 165                 switch (cmsg->cmsg_type)
 166                 {
 167                 case SCM_RIGHTS:
 168                         if (!sock->ops || sock->ops->family != PF_UNIX)
 169                                 goto error;
 170                         err=scm_fp_copy(cmsg, &p->fp);
 171                         if (err<0)
 172                                 goto error;
 173                         break;
 174                 case SCM_CREDENTIALS:
 175                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 176                                 goto error;
 177                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 178                         err = scm_check_creds(&p->creds);
 179                         if (err)
 180                                 goto error;
 181
 182                         if (!p->pid || pid_vnr(p->pid) != p->creds.pid) {
 183                                 struct pid *pid;
 184                                 err = -ESRCH;
 185                                 pid = find_get_pid(p->creds.pid);
 186                                 if (!pid)
 187                                         goto error;
 188                                 put_pid(p->pid);
 189                                 p->pid = pid;
 190                         }
 191
 192                         if (!p->cred ||
 193                             (p->cred->euid != p->creds.uid) ||
 194                             (p->cred->egid != p->creds.gid)) {
 195                                 struct cred *cred;
 196                                 err = -ENOMEM;
 197                                 cred = prepare_creds();
 198                                 if (!cred)
 199                                         goto error;
 200
 201                                 cred->uid = cred->euid = p->creds.uid;
 202                                 cred->gid = cred->egid = p->creds.gid;
 203                                 if (p->cred)
 204                                         put_cred(p->cred);
 205                                 p->cred = cred;
 206                         }
 207                         break;
 208                 default:
 209                         goto error;
 210                 }
 211         }
 212
 213         if (p->fp && !p->fp->count)
 214         {
 215                 kfree(p->fp);
 216                 p->fp = NULL;
 217         }
 218         return 0;
 219
 220 error:
 221         scm_destroy(p);
 222         return err;
 223 }
 224 EXPORT_SYMBOL(__scm_send);
 225
 226 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 227 {
 228         struct cmsghdr __user *cm
 229                 = (__force struct cmsghdr __user *)msg->msg_control;
 230         struct cmsghdr cmhdr;
 231         int cmlen = CMSG_LEN(len);
 232         int err;
 233
 234         if (MSG_CMSG_COMPAT & msg->msg_flags)
 235                 return put_cmsg_compat(msg, level, type, len, data);
 236
 237         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 238                 msg->msg_flags |= MSG_CTRUNC;
 239                 return 0; /* XXX: return error? check spec. */
 240         }
 241         if (msg->msg_controllen < cmlen) {
 242                 msg->msg_flags |= MSG_CTRUNC;
 243                 cmlen = msg->msg_controllen;
 244         }
 245         cmhdr.cmsg_level = level;
 246         cmhdr.cmsg_type = type;
 247         cmhdr.cmsg_len = cmlen;
 248
 249         err = -EFAULT;
 250         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 251                 goto out;
 252         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 253                 goto out;
 254         cmlen = CMSG_SPACE(len);
 255         if (msg->msg_controllen < cmlen)
 256                 cmlen = msg->msg_controllen;
 257         msg->msg_control += cmlen;
 258         msg->msg_controllen -= cmlen;
 259         err = 0;
 260 out:
 261         return err;
 262 }
 263 EXPORT_SYMBOL(put_cmsg);
 264
 265 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 266 {
 267         struct cmsghdr __user *cm
 268                 = (__force struct cmsghdr __user*)msg->msg_control;
 269
 270         int fdmax = 0;
 271         int fdnum = scm->fp->count;
 272         struct file **fp = scm->fp->fp;
 273         int __user *cmfptr;
 274         int err = 0, i;
 275
 276         if (MSG_CMSG_COMPAT & msg->msg_flags) {
 277                 scm_detach_fds_compat(msg, scm);
 278                 return;
 279         }
 280
 281         if (msg->msg_controllen > sizeof(struct cmsghdr))
 282                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 283                          / sizeof(int));
 284
 285         if (fdnum < fdmax)
 286                 fdmax = fdnum;
 287
 288         for (i=0, cmfptr=(__force int __user *)CMSG_DATA(cm); i<fdmax;
 289              i++, cmfptr++)
 290         {
 291                 int new_fd;
 292                 err = security_file_receive(fp[i]);
 293                 if (err)
 294                         break;
 295                 err = get_unused_fd_flags(MSG_CMSG_CLOEXEC & msg->msg_flags
 296                                           ? O_CLOEXEC : 0);
 297                 if (err < 0)
 298                         break;
 299                 new_fd = err;
 300                 err = put_user(new_fd, cmfptr);
 301                 if (err) {
 302                         put_unused_fd(new_fd);
 303                         break;
 304                 }
 305                 /* Bump the usage count and install the file. */
 306                 get_file(fp[i]);
 307                 fd_install(new_fd, fp[i]);
 308         }
 309
 310         if (i > 0)
 311         {
 312                 int cmlen = CMSG_LEN(i*sizeof(int));
 313                 err = put_user(SOL_SOCKET, &cm->cmsg_level);
 314                 if (!err)
 315                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 316                 if (!err)
 317                         err = put_user(cmlen, &cm->cmsg_len);
 318                 if (!err) {
 319                         cmlen = CMSG_SPACE(i*sizeof(int));
 320                         if (msg->msg_controllen < cmlen)
 321                                 cmlen = msg->msg_controllen;
 322                         msg->msg_control += cmlen;
 323                         msg->msg_controllen -= cmlen;
 324                 }
 325         }
 326         if (i < fdnum || (fdnum && fdmax <= 0))
 327                 msg->msg_flags |= MSG_CTRUNC;
 328
 329         /*
 330          * All of the files that fit in the message have had their
 331          * usage counts incremented, so we just free the list.
 332          */
 333         __scm_destroy(scm);
 334 }
 335 EXPORT_SYMBOL(scm_detach_fds);
 336
 337 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 338 {
 339         struct scm_fp_list *new_fpl;
 340         int i;
 341
 342         if (!fpl)
 343                 return NULL;
 344
 345         new_fpl = kmemdup(fpl, offsetof(struct scm_fp_list, fp[fpl->count]),
 346                           GFP_KERNEL);
 347         if (new_fpl) {
 348                 for (i = 0; i < fpl->count; i++)
 349                         get_file(fpl->fp[i]);
 350                 new_fpl->max = new_fpl->count;
 351                 new_fpl->user = get_uid(fpl->user);
 352         }
 353         return new_fpl;
 354 }
 355 EXPORT_SYMBOL(scm_fp_dup);