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