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