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

[zhouyuhang]

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.
>
> > +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.


> > +
> >   static void child_exit(int ret)
> >   {
> >       fflush(stdout);
> > @@ -87,47 +94,36 @@ static int test_clone3_set_tid(struct 
> > __test_metadata *_metadata,
> >       return ret;
> >   }
> >   -struct libcap {
> > -    struct __user_cap_header_struct hdr;
> > -    struct __user_cap_data_struct data[2];
> > -};
> > -
> >   static int set_capability(void)
> >   {
> > -    cap_value_t cap_values[] = { CAP_SETUID, CAP_SETGID };
> > -    struct libcap *cap;
> > -    int ret = -1;
> > -    cap_t caps;
> > -
> > -    caps = cap_get_proc();
> > -    if (!caps) {
> > -        perror("cap_get_proc");
> > +    struct __user_cap_data_struct data[2];
> > +    struct __user_cap_header_struct hdr = {
> > +        .version = _LINUX_CAPABILITY_VERSION_3,
> > +    };
> > +    __u32 cap0 = 1 << CAP_SETUID | 1 << CAP_SETGID;
> > +    __u32 cap1 = 1 << (CAP_CHECKPOINT_RESTORE - 32);
> > +    int ret;
> > +
> > +    ret = capget(&hdr, data);
> > +    if (ret) {
> > +        perror("capget");
> >           return -1;
> >       }
> >         /* Drop all capabilities */
> > -    if (cap_clear(caps)) {
> > -        perror("cap_clear");
> > -        goto out;
> > -    }
> > +    memset(&data, 0, sizeof(data));
> >   -    cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_values, CAP_SET);
> > -    cap_set_flag(caps, CAP_PERMITTED, 2, cap_values, CAP_SET);
> > +    data[0].effective |= cap0;
> > +    data[0].permitted |= cap0;
> >   -    cap = (struct libcap *) caps;
> > +    data[1].effective |= cap1;
> > +    data[1].permitted |= cap1;
> >   -    /* 40 -> CAP_CHECKPOINT_RESTORE */
> > -    cap->data[1].effective |= 1 << (40 - 32);
> > -    cap->data[1].permitted |= 1 << (40 - 32);
> > -
> > -    if (cap_set_proc(caps)) {
> > -        perror("cap_set_proc");
> > -        goto out;
> > +    ret = capset(&hdr, data);
> > +    if (ret) {
> > +        perror("capset");
> > +        return -1;
> >       }
> > -    ret = 0;
> > -out:
> > -    if (cap_free(caps))
> > -        perror("cap_free");
> >       return ret;
> >   }
>
> thanks,
> -- Shuah