pac...@kosh.dhis.org hat am Mon 27. Jun, 23:02 (-0500) geschrieben: > =?iso-8859-1?Q?J=F6rg?= Sommer writes: > > I don't know, why dd thinks something went wrong. llseek() and fstat64() > > didn't return an error. Accessing the file with Ruby yields the expected > > result. > > I don't speak ruby, but that sounds unlikely. Would it do a ptrace > behind your back? Or did you maybe think it succeeded when actually it > just didn't report the errors it encountered? You should strace that too.
% cat /tmp/mem-cat.c
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <unistd.h>
#define ASSERT(cmp, msg) if (!(cmp)) { perror(msg); return EXIT_FAILURE; }
int main(void)
{
int fd_in = open("/proc/self/mem", O_RDONLY);
ASSERT(fd_in != -1, "open(/p/s/m)");
int fd_out = open("/tmp/mem-cat.out", O_WRONLY | O_CREAT, 0600);
ASSERT(fd_out != -1, "open(/t/m)");
off_t ret = lseek(fd_in, 0x100000, SEEK_SET);
printf("seek: %ld\n", ret);
ASSERT(ret != (off_t)-1, "lseek");
size_t buf_len = 0x103000 - 0x100000;
char* buf = malloc(buf_len);
ASSERT(buf != NULL, "malloc");
ssize_t read_len = read(fd_in, buf, buf_len);
printf("read: %d\n", read_len);
ASSERT(read_len == (ssize_t)buf_len, "read");
ssize_t write_len = write(fd_out, buf, buf_len);
printf("write: %d\n", write_len);
ASSERT(write_len == (ssize_t)buf_len, "write");
return EXIT_SUCCESS;
}
% make /tmp/mem-cat
cc -O2 -fPIC -fPIE -Wall -Wformat=2 -Wunused -Wlogical-op -Wundef -Wextra
-Wswitch-enum -Wshadow -Wpointer-arith -Wcast-qual -Wcast-align
-Wwrite-strings -Wconversion -D_FORTIFY_SOURCE=2 -fstack-protector
-Wbad-function-cast -Wnested-externs -Wl,-zrelro,-pie /tmp/mem-cat.c -o
/tmp/mem-cat
% /tmp/mem-cat
seek: 1048576
read: 12288
write: 12288
% file /tmp/mem-cat.out
/tmp/mem-cat.out: ELF 32-bit MSB shared object, PowerPC or cisco 4500, version
1 (SYSV), dynamically linked, stripped
Bye, Jörg.
--
Die Erde ist das einzigste Irrenhaus, das von seinen eigenen Insassen
verwaltet wird.
(U. Schmidt)
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