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selftests/pidfd: test that fields beyond the struct size are not reported

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PIDFD_GET_INFO must not set the mask bit of a field that lies beyond
the struct size encoded in the ioctl command. Add a test that requests
the coredump fields and the supported mask with PIDFD_INFO_SIZE_VER0
over a full-size, poisoned struct, and checks that the mask names none
of those fields and that the poison behind the first 64 bytes is
intact.

Add fallback definitions of PIDFD_INFO_SIZE_VER0 to VER3 to pidfd.h,
like the other uapi constants there.

Signed-off-by: Nickolai Zeldovich <nickolai@csail.mit.edu>
Link: https://patch.msgid.link/20261024041334.831273-3-nickolai@csail.mit.edu
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
This commit is contained in:
Nickolai Zeldovich 2026-10-24 00:13:34 -04:00 committed by Christian Brauner
parent 1534c37167
commit 28767d4934
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GPG Key ID: 91C61BC06578DCA2
2 changed files with 64 additions and 0 deletions
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16
tools/testing/selftests/pidfd/pidfd.h
View File

@ -160,6 +160,22 @@
#define PIDFD_INFO_COREDUMP_CODE (1UL << 7)
#endif
#ifndef PIDFD_INFO_SIZE_VER0
#define PIDFD_INFO_SIZE_VER0 64 /* sizeof first published struct */
#endif
#ifndef PIDFD_INFO_SIZE_VER1
#define PIDFD_INFO_SIZE_VER1 72 /* sizeof second published struct */
#endif
#ifndef PIDFD_INFO_SIZE_VER2
#define PIDFD_INFO_SIZE_VER2 80 /* sizeof third published struct */
#endif
#ifndef PIDFD_INFO_SIZE_VER3
#define PIDFD_INFO_SIZE_VER3 88 /* sizeof fourth published struct */
#endif
#ifndef PIDFD_COREDUMPED
#define PIDFD_COREDUMPED (1U << 0) /* Did crash and... */
#endif

48
tools/testing/selftests/pidfd/pidfd_info_test.c
View File

@ -764,4 +764,52 @@ TEST(supported_mask_with_other_fields)
close(pidfd);
}
/*
* Test: fields beyond the caller's struct size are not reported
*
* Request the coredump and supported_mask fields with a struct of the
* first published size. None of those fields fit, so the returned mask
* must not name them and the memory behind the struct must be untouched.
*/
TEST(info_size_ver0_mask)
{
struct pidfd_info info = {
.mask = PIDFD_INFO_COREDUMP | PIDFD_INFO_SUPPORTED_MASK,
.coredump_mask = 0xdeadbeef,
.coredump_signal = 0xdeadbeef,
.coredump_code = 0xdeadbeef,
.supported_mask = 0xdeadbeefdeadbeefULL,
};
unsigned int cmd = _IOC(_IOC_READ | _IOC_WRITE, PIDFS_IOCTL_MAGIC, 11,
PIDFD_INFO_SIZE_VER0);
int pidfd;
pid_t pid;
pid = create_child(&pidfd, 0);
ASSERT_GE(pid, 0);
if (pid == 0)
pause();
ASSERT_EQ(ioctl(pidfd, cmd, &info), 0);
/* The fields that fit are reported as usual. */
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_PID));
ASSERT_TRUE(!!(info.mask & PIDFD_INFO_CREDS));
/* The fields that do not fit are neither reported nor written. */
ASSERT_FALSE(!!(info.mask & (PIDFD_INFO_COREDUMP |
PIDFD_INFO_COREDUMP_SIGNAL |
PIDFD_INFO_COREDUMP_CODE |
PIDFD_INFO_SUPPORTED_MASK)));
ASSERT_EQ(info.coredump_mask, 0xdeadbeef);
ASSERT_EQ(info.coredump_signal, 0xdeadbeef);
ASSERT_EQ(info.coredump_code, 0xdeadbeef);
ASSERT_EQ(info.supported_mask, 0xdeadbeefdeadbeefULL);
sys_pidfd_send_signal(pidfd, SIGKILL, NULL, 0);
sys_waitid(P_PIDFD, pidfd, NULL, WEXITED);
close(pidfd);
}
TEST_HARNESS_MAIN