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/signal.h>
  13 #include <linux/errno.h>
  14 #include <linux/sched.h>
  15 #include <linux/mm.h>
  16 #include <linux/kernel.h>
  17 #include <linux/major.h>
  18 #include <linux/stat.h>
  19 #include <linux/socket.h>
  20 #include <linux/file.h>
  21 #include <linux/fcntl.h>
  22 #include <linux/net.h>
  23 #include <linux/interrupt.h>
  24 #include <linux/netdevice.h>
  25
  26 #include <asm/system.h>
  27 #include <asm/uaccess.h>
  28
  29 #include <linux/inet.h>
  30 #include <net/ip.h>
  31 #include <net/protocol.h>
  32 #include <net/tcp.h>
  33 #include <net/udp.h>
  34 #include <linux/skbuff.h>
  35 #include <net/sock.h>
  36 #include <net/scm.h>
  37
  38
  39 /*
  40  *      Only allow a user to send credentials, that they could set with
  41  *      setu(g)id.
  42  */
  43
  44 static __inline__ int scm_check_creds(struct ucred *creds)
  45 {
  46         if ((creds->pid == current->pid || capable(CAP_SYS_ADMIN)) &&
  47             ((creds->uid == current->uid || creds->uid == current->euid ||
  48               creds->uid == current->suid) || capable(CAP_SETUID)) &&
  49             ((creds->gid == current->gid || creds->gid == current->egid ||
  50               creds->gid == current->sgid) || capable(CAP_SETGID))) {
  51                return 0;
  52         }
  53         return -EPERM;
  54 }
  55
  56 static int scm_fp_copy(struct cmsghdr *cmsg, struct scm_fp_list **fplp)
  57 {
  58         int *fdp = (int*)CMSG_DATA(cmsg);
  59         struct scm_fp_list *fpl = *fplp;
  60         struct file **fpp;
  61         int i, num;
  62
  63         num = (cmsg->cmsg_len - CMSG_ALIGN(sizeof(struct cmsghdr)))/sizeof(int);
  64
  65         if (num <= 0)
  66                 return 0;
  67
  68         if (num > SCM_MAX_FD)
  69                 return -EINVAL;
  70
  71         if (!fpl)
  72         {
  73                 fpl = kmalloc(sizeof(struct scm_fp_list), GFP_KERNEL);
  74                 if (!fpl)
  75                         return -ENOMEM;
  76                 *fplp = fpl;
  77                 fpl->count = 0;
  78         }
  79         fpp = &fpl->fp[fpl->count];
  80
  81         if (fpl->count + num > SCM_MAX_FD)
  82                 return -EINVAL;
  83
  84         /*
  85          *      Verify the descriptors and increment the usage count.
  86          */
  87
  88         for (i=0; i< num; i++)
  89         {
  90                 int fd = fdp[i];
  91                 struct file *file;
  92
  93                 if (fd < 0 || !(file = fget(fd)))
  94                         return -EBADF;
  95                 *fpp++ = file;
  96                 fpl->count++;
  97         }
  98         return num;
  99 }
 100
 101 void __scm_destroy(struct scm_cookie *scm)
 102 {
 103         struct scm_fp_list *fpl = scm->fp;
 104         int i;
 105
 106         if (fpl) {
 107                 scm->fp = NULL;
 108                 for (i=fpl->count-1; i>=0; i--)
 109                         fput(fpl->fp[i]);
 110                 kfree(fpl);
 111         }
 112 }
 113
 114 int __scm_send(struct socket *sock, struct msghdr *msg, struct scm_cookie *p)
 115 {
 116         struct cmsghdr *cmsg;
 117         int err;
 118
 119         for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg))
 120         {
 121                 err = -EINVAL;
 122
 123                 /* Verify that cmsg_len is at least sizeof(struct cmsghdr) */
 124                 /* The first check was omitted in <= 2.2.5. The reasoning was
 125                    that parser checks cmsg_len in any case, so that
 126                    additional check would be work duplication.
 127                    But if cmsg_level is not SOL_SOCKET, we do not check
 128                    for too short ancillary data object at all! Oops.
 129                    OK, let's add it...
 130                  */
 131                 if (cmsg->cmsg_len < sizeof(struct cmsghdr) ||
 132                     (unsigned long)(((char*)cmsg - (char*)msg->msg_control)
 133                                     + cmsg->cmsg_len) > msg->msg_controllen)
 134                         goto error;
 135
 136                 if (cmsg->cmsg_level != SOL_SOCKET)
 137                         continue;
 138
 139                 switch (cmsg->cmsg_type)
 140                 {
 141                 case SCM_RIGHTS:
 142                         err=scm_fp_copy(cmsg, &p->fp);
 143                         if (err<0)
 144                                 goto error;
 145                         break;
 146                 case SCM_CREDENTIALS:
 147                         if (cmsg->cmsg_len != CMSG_LEN(sizeof(struct ucred)))
 148                                 goto error;
 149                         memcpy(&p->creds, CMSG_DATA(cmsg), sizeof(struct ucred));
 150                         err = scm_check_creds(&p->creds);
 151                         if (err)
 152                                 goto error;
 153                         break;
 154                 default:
 155                         goto error;
 156                 }
 157         }
 158
 159         if (p->fp && !p->fp->count)
 160         {
 161                 kfree(p->fp);
 162                 p->fp = NULL;
 163         }
 164         return 0;
 165
 166 error:
 167         scm_destroy(p);
 168         return err;
 169 }
 170
 171 int put_cmsg(struct msghdr * msg, int level, int type, int len, void *data)
 172 {
 173         struct cmsghdr *cm = (struct cmsghdr*)msg->msg_control;
 174         struct cmsghdr cmhdr;
 175         int cmlen = CMSG_LEN(len);
 176         int err;
 177
 178         if (cm==NULL || msg->msg_controllen < sizeof(*cm)) {
 179                 msg->msg_flags |= MSG_CTRUNC;
 180                 return 0; /* XXX: return error? check spec. */
 181         }
 182         if (msg->msg_controllen < cmlen) {
 183                 msg->msg_flags |= MSG_CTRUNC;
 184                 cmlen = msg->msg_controllen;
 185         }
 186         cmhdr.cmsg_level = level;
 187         cmhdr.cmsg_type = type;
 188         cmhdr.cmsg_len = cmlen;
 189
 190         err = -EFAULT;
 191         if (copy_to_user(cm, &cmhdr, sizeof cmhdr))
 192                 goto out;
 193         if (copy_to_user(CMSG_DATA(cm), data, cmlen - sizeof(struct cmsghdr)))
 194                 goto out;
 195         cmlen = CMSG_SPACE(len);
 196         msg->msg_control += cmlen;
 197         msg->msg_controllen -= cmlen;
 198         err = 0;
 199 out:
 200         return err;
 201 }
 202
 203 void scm_detach_fds(struct msghdr *msg, struct scm_cookie *scm)
 204 {
 205         struct cmsghdr *cm = (struct cmsghdr*)msg->msg_control;
 206
 207         int fdmax = 0;
 208         int fdnum = scm->fp->count;
 209         struct file **fp = scm->fp->fp;
 210         int *cmfptr;
 211         int err = 0, i;
 212
 213         if (msg->msg_controllen > sizeof(struct cmsghdr))
 214                 fdmax = ((msg->msg_controllen - sizeof(struct cmsghdr))
 215                          / sizeof(int));
 216
 217         if (fdnum < fdmax)
 218                 fdmax = fdnum;
 219
 220         for (i=0, cmfptr=(int*)CMSG_DATA(cm); i<fdmax; i++, cmfptr++)
 221         {
 222                 int new_fd;
 223                 err = get_unused_fd();
 224                 if (err < 0)
 225                         break;
 226                 new_fd = err;
 227                 err = put_user(new_fd, cmfptr);
 228                 if (err) {
 229                         put_unused_fd(new_fd);
 230                         break;
 231                 }
 232                 /* Bump the usage count and install the file. */
 233                 get_file(fp[i]);
 234                 fd_install(new_fd, fp[i]);
 235         }
 236
 237         if (i > 0)
 238         {
 239                 int cmlen = CMSG_LEN(i*sizeof(int));
 240                 if (!err)
 241                         err = put_user(SOL_SOCKET, &cm->cmsg_level);
 242                 if (!err)
 243                         err = put_user(SCM_RIGHTS, &cm->cmsg_type);
 244                 if (!err)
 245                         err = put_user(cmlen, &cm->cmsg_len);
 246                 if (!err) {
 247                         cmlen = CMSG_SPACE(i*sizeof(int));
 248                         msg->msg_control += cmlen;
 249                         msg->msg_controllen -= cmlen;
 250                 }
 251         }
 252         if (i < fdnum || (fdnum && fdmax <= 0))
 253                 msg->msg_flags |= MSG_CTRUNC;
 254
 255         /*
 256          * All of the files that fit in the message have had their
 257          * usage counts incremented, so we just free the list.
 258          */
 259         __scm_destroy(scm);
 260 }
 261
 262 struct scm_fp_list *scm_fp_dup(struct scm_fp_list *fpl)
 263 {
 264         struct scm_fp_list *new_fpl;
 265         int i;
 266
 267         if (!fpl)
 268                 return NULL;
 269
 270         new_fpl = kmalloc(sizeof(*fpl), GFP_KERNEL);
 271         if (new_fpl) {
 272                 for (i=fpl->count-1; i>=0; i--)
 273                         get_file(fpl->fp[i]);
 274                 memcpy(new_fpl, fpl, sizeof(*fpl));
 275         }
 276         return new_fpl;
 277 }