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memfd: add test for COW on MAP_PRIVATE and F_SEAL_FUTURE_WRITE mappings 

In this test, the parent and child both have writable private mappings.
The test shows that without the patch in this series, the parent and
child shared the same memory which is incorrect.  In other words, COW
needs to be triggered so any writes to child's copy stays local to the
child.

Link: http://lkml.kernel.org/r/20191107195355.80608-2-joel@joelfernandes.org
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Nicolas Geoffray <ngeoffray@google.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Joel Fernandes (Google) 2019-11-30 17:53:31 -08:00 committed by Linus Torvalds
parent 05d351102d
commit 2e53c4e1c8
1 changed files with 36 additions and 0 deletions
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36
tools/testing/selftests/memfd/memfd_test.c
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@ -290,6 +290,40 @@ static void mfd_assert_read_shared(int fd)
munmap(p, mfd_def_size);
}
static void mfd_assert_fork_private_write(int fd)
{
int *p;
pid_t pid;
p = mmap(NULL,
mfd_def_size,
PROT_READ | PROT_WRITE,
MAP_PRIVATE,
fd,
0);
if (p == MAP_FAILED) {
printf("mmap() failed: %m\n");
abort();
}
p[0] = 22;
pid = fork();
if (pid == 0) {
p[0] = 33;
exit(0);
} else {
waitpid(pid, NULL, 0);
if (p[0] != 22) {
printf("MAP_PRIVATE copy-on-write failed: %m\n");
abort();
}
}
munmap(p, mfd_def_size);
}
static void mfd_assert_write(int fd)
{
ssize_t l;
@ -760,6 +794,8 @@ static void test_seal_future_write(void)
mfd_assert_read_shared(fd2);
mfd_fail_write(fd2);
mfd_assert_fork_private_write(fd);
munmap(p, mfd_def_size);
close(fd2);
close(fd);