src/pklock.c

   1 /*      PKLOCK.C
   2  *
   3  *      locking routines as modified by Petri Kutvonen
   4  */
   5
   6 #include "estruct.h"
   7 #include "edef.h"
   8 #include "efunc.h"
   9
  10 #if (FILOCK && BSD) || SVR4
  11 #include <sys/types.h>
  12 #include <sys/stat.h>
  13 #include <unistd.h>
  14 #include <stdio.h>
  15 #include <fcntl.h>
  16 #ifdef SVR4
  17 #include <string.h>
  18 #else
  19 #include <strings.h>
  20 #endif
  21 #include <errno.h>
  22
  23 #define MAXLOCK 512
  24 #define MAXNAME 128
  25
  26 #if defined(SVR4) && ! defined(__linux__)
  27 #include <sys/systeminfo.h>
  28
  29 int gethostname(char *name, int namelen)
  30 {
  31         return sysinfo(SI_HOSTNAME, name, namelen);
  32 }
  33 #endif
  34
  35
  36
  37 /**********************
  38  *
  39  * if successful, returns NULL
  40  * if file locked, returns username of person locking the file
  41  * if other error, returns "LOCK ERROR: explanation"
  42  *
  43  *********************/
  44 char *dolock(char *fname)
  45 {
  46         int fd, n;
  47         static char lname[MAXLOCK], locker[MAXNAME + 1];
  48         int mask;
  49         struct stat sbuf;
  50
  51         strcat(strcpy(lname, fname), ".lock~");
  52
  53         /* check that we are not being cheated, qname must point to     */
  54         /* a regular file - even this code leaves a small window of     */
  55         /* vulnerability but it is rather hard to exploit it            */
  56
  57 #if defined(S_IFLNK)
  58         if (lstat(lname, &sbuf) == 0)
  59 #else
  60         if (stat(lname, &sbuf) == 0)
  61 #endif
  62 #if defined(S_ISREG)
  63                 if (!S_ISREG(sbuf.st_mode))
  64 #else
  65                 if (!(((sbuf.st_mode) & 070000) == 0))  /* SysV R2 */
  66 #endif
  67                         return "LOCK ERROR: not a regular file";
  68
  69         mask = umask(0);
  70         fd = open(lname, O_RDWR | O_CREAT, 0666);
  71         umask(mask);
  72         if (fd < 0) {
  73                 if (errno == EACCES)
  74                         return NULL;
  75 #ifdef EROFS
  76                 if (errno == EROFS)
  77                         return NULL;
  78 #endif
  79                 return "LOCK ERROR: cannot access lock file";
  80         }
  81         if ((n = read(fd, locker, MAXNAME)) < 1) {
  82                 lseek(fd, 0, SEEK_SET);
  83 /*              strcpy(locker, getlogin()); */
  84                 cuserid(locker);
  85                 strcat(locker + strlen(locker), "@");
  86                 gethostname(locker + strlen(locker), 64);
  87                 write(fd, locker, strlen(locker));
  88                 close(fd);
  89                 return NULL;
  90         }
  91         locker[n > MAXNAME ? MAXNAME : n] = 0;
  92         return locker;
  93 }
  94
  95
  96 /*********************
  97  *
  98  * undolock -- unlock the file fname
  99  *
 100  * if successful, returns NULL
 101  * if other error, returns "LOCK ERROR: explanation"
 102  *
 103  *********************/
 104
 105 char *undolock(char *fname)
 106 {
 107         static char lname[MAXLOCK];
 108
 109         strcat(strcpy(lname, fname), ".lock~");
 110         if (unlink(lname) != 0) {
 111                 if (errno == EACCES || errno == ENOENT)
 112                         return NULL;
 113 #ifdef EROFS
 114                 if (errno == EROFS)
 115                         return NULL;
 116 #endif
 117                 return "LOCK ERROR: cannot remove lock file";
 118         }
 119
 120         return NULL;
 121 }
 122 #endif