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pklock.c
121 lines (105 loc) · 2.4 KB
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pklock.c
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/* PKLOCK.C
*
* locking routines as modified by Petri Kutvonen
*/
#include "estruct.h"
#include "edef.h"
#include "efunc.h"
#if (FILOCK && BSD) || SVR4
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#ifdef SVR4
#include <string.h>
#else
#include <strings.h>
#endif
#include <errno.h>
#define MAXLOCK 512
#define MAXNAME 128
#if defined(SVR4) && ! defined(__linux__)
#include <sys/systeminfo.h>
int gethostname(char *name, int namelen)
{
return sysinfo(SI_HOSTNAME, name, namelen);
}
#endif
/**********************
*
* if successful, returns NULL
* if file locked, returns username of person locking the file
* if other error, returns "LOCK ERROR: explanation"
*
*********************/
char *dolock(char *fname)
{
int fd, n;
static char lname[MAXLOCK], locker[MAXNAME + 1];
int mask;
struct stat sbuf;
strcat(strcpy(lname, fname), ".lock~");
/* check that we are not being cheated, qname must point to */
/* a regular file - even this code leaves a small window of */
/* vulnerability but it is rather hard to exploit it */
#if defined(S_IFLNK)
if (lstat(lname, &sbuf) == 0)
#else
if (stat(lname, &sbuf) == 0)
#endif
#if defined(S_ISREG)
if (!S_ISREG(sbuf.st_mode))
#else
if (!(((sbuf.st_mode) & 070000) == 0)) /* SysV R2 */
#endif
return "LOCK ERROR: not a regular file";
mask = umask(0);
fd = open(lname, O_RDWR | O_CREAT, 0666);
umask(mask);
if (fd < 0) {
if (errno == EACCES)
return NULL;
#ifdef EROFS
if (errno == EROFS)
return NULL;
#endif
return "LOCK ERROR: cannot access lock file";
}
if ((n = read(fd, locker, MAXNAME)) < 1) {
lseek(fd, 0, SEEK_SET);
/* strcpy(locker, getlogin()); */
cuserid(locker);
strcat(locker + strlen(locker), "@");
gethostname(locker + strlen(locker), 64);
write(fd, locker, strlen(locker));
close(fd);
return NULL;
}
locker[n > MAXNAME ? MAXNAME : n] = 0;
return locker;
}
/*********************
*
* undolock -- unlock the file fname
*
* if successful, returns NULL
* if other error, returns "LOCK ERROR: explanation"
*
*********************/
char *undolock(char *fname)
{
static char lname[MAXLOCK];
strcat(strcpy(lname, fname), ".lock~");
if (unlink(lname) != 0) {
if (errno == EACCES || errno == ENOENT)
return NULL;
#ifdef EROFS
if (errno == EROFS)
return NULL;
#endif
return "LOCK ERROR: cannot remove lock file";
}
return NULL;
}
#endif