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SubjectDM Regression in 4.16-rc1 - read() returns data when it shouldn't

the commit (found by bisect)

commit 18a25da84354c6bb655320de6072c00eda6eb602
Author: NeilBrown <>
Date: Wed Sep 6 09:43:28 2017 +1000

dm: ensure bio submission follows a depth-first tree walk

cause serious regression while reading from DM device.

The reproducer is below, basically it tries to simulate failure we see in cryptsetup
regression test: we have DM device with error and zero target and try to read
"passphrase" from it (it is test for 64 bit offset error path):

Test device:
# dmsetup table test
0 10000000 error
10000000 1000000 zero

We try to run this operation:
lseek64(fd, 5119999988, SEEK_CUR); // this should seek to error target sector
read(fd, buf, 13); // this should fail, if we seek to error part of the device

While on 4.15 the read properly fails:
Seek returned 5119999988.
Read returned -1.

for 4.16 it actually succeeds returning some random data
(perhaps kernel memory, so this bug is even more dangerous):
Seek returned 5119999988.
Read returned 13.

Full reproducer below:

#define _GNU_SOURCE
#include <stdio.h>
#include <stddef.h>
#include <stdint.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <inttypes.h>

int main (int argc, char *argv[])
char buf[13];
int fd;
//uint64_t offset64 = 5119999999;
uint64_t offset64 = 5119999988;
off64_t r;
ssize_t bytes;

system("echo -e \'0 10000000 error\'\\\\n\'10000000 1000000 zero\' | dmsetup create test");

fd = open("/dev/mapper/test", O_RDONLY);
if (fd == -1) {
printf("open fail\n");
return 1;

r = lseek64(fd, offset64, SEEK_CUR);
printf("Seek returned %" PRIu64 ".\n", r);
if (r < 0) {
printf("seek fail\n");
return 2;

bytes = read(fd, buf, 13);
printf("Read returned %d.\n", (int)bytes);

return 0;

Please let me know if you need more info to reproduce it.


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