Re: [PATCH] selftests: clone3: Use the capget and capset syscall directly

From: zhouyuhang
Date: Tue Oct 15 2024 - 05:01:40 EST


在 2024/10/15 06:38, Shuah Khan 写道:
On 10/12/24 02:28, zhouyuhang wrote:

On 2024/10/11 22:21, Shuah Khan wrote:
On 10/11/24 00:59, zhouyuhang wrote:

On 2024/10/10 23:50, Shuah Khan wrote:
On 10/10/24 06:16, zhouyuhang wrote:
From: zhouyuhang <zhouyuhang@xxxxxxxxxx>

The libcap commit aca076443591 ("Make cap_t operations thread safe.") added a
__u8 mutex at the beginning of the struct _cap_struct,it changes the offset of
the members in the structure that breaks the assumption made in the "struct libcap"
definition in clone3_cap_checkpoint_restore.c.So use the capget and capset syscall
directly and remove the libcap library dependency like the commit 663af70aabb7
("bpf: selftests: Add helpers to directly use the capget and capset syscall") does.


NIT: grammar and comma spacing. Please fix those for readability.
e.g: Change "struct _cap_struct,it" to "struct _cap_struct, it"
Fix others as well.


Thanks, I'll fix it in V2


Signed-off-by: zhouyuhang <zhouyuhang@xxxxxxxxxx>
---
  tools/testing/selftests/clone3/Makefile       |  1 -
  .../clone3/clone3_cap_checkpoint_restore.c    | 60 +++++++++----------
  2 files changed, 28 insertions(+), 33 deletions(-)

diff --git a/tools/testing/selftests/clone3/Makefile b/tools/testing/selftests/clone3/Makefile
index 84832c369a2e..59d26e8da8d2 100644
--- a/tools/testing/selftests/clone3/Makefile
+++ b/tools/testing/selftests/clone3/Makefile
@@ -1,6 +1,5 @@
  # SPDX-License-Identifier: GPL-2.0
  CFLAGS += -g -std=gnu99 $(KHDR_INCLUDES)
-LDLIBS += -lcap
    TEST_GEN_PROGS := clone3 clone3_clear_sighand clone3_set_tid \
      clone3_cap_checkpoint_restore
diff --git a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
index 3c196fa86c99..111912e2aead 100644
--- a/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
+++ b/tools/testing/selftests/clone3/clone3_cap_checkpoint_restore.c
@@ -15,7 +15,7 @@
  #include <stdio.h>
  #include <stdlib.h>
  #include <stdbool.h>
-#include <sys/capability.h>
+#include <linux/capability.h>
  #include <sys/prctl.h>
  #include <sys/syscall.h>
  #include <sys/types.h>
@@ -27,6 +27,13 @@
  #include "../kselftest_harness.h"
  #include "clone3_selftests.h"
  +#ifndef CAP_CHECKPOINT_RESTORE
+#define CAP_CHECKPOINT_RESTORE 40
+#endif
+

Why is this necessary? This is defined in linux/capability.h.

Sorry for not noticing this before.
This is to be compatible with some older versions of linux/capability.h that do not define this macro.


+int capget(cap_user_header_t header, cap_user_data_t data);
+int capset(cap_user_header_t header, const cap_user_data_t data);

In general prototypes such as these should be defined in header
file. Why are we defining these here?

These are defined in sys/capability.h

I don't understand this change. You are removing sys/capability.h
which requires you to add these defines here. This doesn't
sound like a correct solution to me.


I tested it on my machine without libcap-dev installed, the /usr/include/linux/capability.h

is on this machine by default. Successfully compiled using #include <linux/capability.h>

but not with #include <sys/capability.h>. This patch removes libcap library dependencies.

And we don't use any part of sys/capability.h other than these two syscalls. So I think that's why it's necessary.

You are changing the code to not include sys/capability.h
What happens if sys/capability.h along with linux/capability.h

Do you see problems?


I'm sorry, maybe I wasn't clear enough.
When we install the libcap library it will have the following output:

test@test:~/work/libcap$ sudo make install | grep capability
install -m 0644 include/sys/capability.h /usr/include/sys
install -m 0644 include/sys/capability.h /usr/include/sys
/usr/share/man/man5 capability.conf.5 \

It installs sys/capability.h in the correct location, but does not

install linux/capability.h, so sys/capability.h is bound to the libcap library

It won't install inux/capability.h unless you run "make headers" in
the kernel repo.


and they will either exist or disappear together. Now I want to remove

the dependency of the test on libcap library so I changed the code that it

does not contain sys/capability.h but instead linux/capability.h,

so that the test can compile successfully without libcap being installed,

these two syscalls are not declared in linux/capability.h(It is sufficient for test use except for these two syscalls)

so we need to declare them here. I think that's why the commit 663af70aabb7

("bpf: selftests: Add helpers to directly use the capget and capset syscall") I refered to

does the same thing. As for your question "What happens if sys/capability.h along

with linux/capability.h", I haven't found the problem yet, I sincerely hope you can

help me improve this code. Thank you very much.

Try this:

Run make headers in the kernel repo.
Build without making any changes.
Then add you changes and add linux/capability.h to include files

Tell me what happens.

The change you are making isn't correct. Because you don't want to
define system calls locally in your source file.


Thanks, I see.
Maybe I should move them to a new header file and resend a patch.

thanks,
-- Shuah