PROBLEM: mmap MAP_SHARED does not update mtime or ctime
mmap'ing a file with MAP_SHARED and writeable, modifing the memory
then closeing does not update the file mod time or change time
risking that incremental dumps will not dump the file and is
a possible security problem as one can change a file without
changing the mod-time. C program showing the problem follows.
Program has been run only against ext2 filesystems.
This is a regression from the 2.2 series which correctly updates
mtime and ctime. Problem also appeared on 2.4.8
Jeff Anton
Linux chaos 2.4.9 #1 Sun Aug 19 09:29:48 PDT 2001 i586 unknown
Gnu C 2.95.3
Gnu make 3.77
binutils 2.10.1
usage: fdformat [ -n ] device
mount 2.7f
modutils 2.4.1
e2fsprogs 1.19
PPP 2.3.11
Linux C Library 2.2.2
Dynamic linker (ldd) 2.2.2
Linux C++ Library 27.2.8
Linux C++ Library 27.2.8
Procps 1.2.7
Net-tools 1.51
Kbd command
Sh-utils 1.16
Modules Loaded eepro100 binfmt_misc nls_iso8859-1 nls_cp437
msdos fat
_____________
#include <stddef.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/mman.h>
#include <stdio.h>
const char fname[] = "testfile";
void
statfile(const char *f)
{
struct stat sb;
if (stat(f, &sb) < 0)
perror(f);
else {
printf("atime\t%lu\n", sb.st_atime);
printf("mtime\t%lu\n", sb.st_mtime);
printf("ctime\t%lu\n", sb.st_ctime);
}
}
void
createfile(const char *f)
{
int fd = open(f, O_CREAT|O_RDWR, 0666);
if (fd < 0)
perror("open-create");
else {
if (ftruncate(fd, 0x2000) < 0)
perror("ftruncate");
if (close(fd) < 0)
perror("close");
}
}
void
mmapchange(const char *f)
{
int fd = open(f, O_RDWR);
void *a = mmap(NULL, 0x2000, PROT_READ|PROT_WRITE, MAP_SHARED, fd,
0);
if (a) {
long *l = (long *)a;
/* touch the memory */
++*l;
} else
perror("mmap");
if (munmap(a, 0x2000) < 0)
perror("munmap");
if (close(fd) < 0)
perror("close");
}
int
main()
{
createfile(fname);
statfile(fname);
sleep(10);
mmapchange(fname);
statfile(fname);
if (unlink(fname) < 0)
perror("unlink");
return 0;
}
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This archive was generated by hypermail 2b29 : Thu Aug 23 2001 - 21:00:33 EST