[LTP] [RFC PATCH 1/1] creat09: Fix on more restrictive umask

[xuyang2018.jy@fujitsu.com]

Hi Darrick, Jack

Petr meet a problem when running creat09 on xfs, ext4 doesn't have problem.

It seems xfs will still use umask when enable default acl, but ext4 will 
not.

As umask2 manpage , it said
"Alternatively, if the parent directory has a default ACL (see acl(5)), 
the umask is ignored, the default ACL is inherited, the permission bits 
are set based on the inherited ACL, and permission bits absent
        in the mode argument are turned off.
"

It seem xfs doesn't obey this rule.

the xfs calltrace as below:

   will use  inode_init_owner(struct user_namespace *mnt_userns, 
structinode *inode)

  296.760675]  xfs_init_new_inode+0x10e/0x6c0
[  296.760678]  xfs_create+0x401/0x610
   will use posix_acl_create(dir, &mode, &default_acl, &acl);
[  296.760681]  xfs_generic_create+0x123/0x2e0
[  296.760684]  ? _raw_spin_unlock+0x16/0x30
[  296.760687]  path_openat+0xfb8/0x1210
[  296.760689]  do_filp_open+0xb4/0x120
[  296.760691]  ? file_tty_write.isra.31+0x203/0x340
[  296.760697]  ? __check_object_size+0x150/0x170
[  296.760699]  do_sys_openat2+0x242/0x310
[  296.760702]  do_sys_open+0x4b/0x80
[  296.760704]  do_syscall_64+0x3a/0x80


the ext4 calltrace as below:
[  296.460999]  __ext4_new_inode+0xe07/0x1780 [ext4]
posix_acl_create(dir, &inode->i_mode, &default_acl, &acl);
[  296.461035]  ext4_create+0x106/0x1c0 [ext4]
[  296.461059]  path_openat+0xfb8/0x1210
[  296.461062]  do_filp_open+0xb4/0x120
[  296.461065]  ? __check_object_size+0x150/0x170
[  296.461068]  do_sys_openat2+0x242/0x310
[  296.461070]  do_sys_open+0x4b/0x80
[  296.461073]  do_syscall_64+0x3a/0x80
[  296.461077]  entry_SYSCALL_64_after_hwframe+0x44/0xae

I guess xfs modify its mode value instead of inode->i_mode in 
posix_acl_create by using current->umask value, so inode_init_owner 
doesn't clear no-sgid bits on created file because of missing S_IXGRP.

Is it a kernel bug?

Best Regards
Yang Xu

> Hi Petr
>
> It fails because the create file without S_IXGRP mode, then we miss
> remove S_ISGID[1] bit.
>
> But I don't known why other filesystem doesn't have this problem.
>
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/inode.c#n2249
>
> Best Regards
> Yang Xu
>> XFS fails on umask 0077:
>>
>> tst_test.c:1528: TINFO: Testing on xfs
>> tst_test.c:997: TINFO: Formatting /dev/loop0 with xfs opts='' extra opts=''
>> tst_test.c:1458: TINFO: Timeout per run is 0h 05m 00s
>> creat09.c:61: TINFO: User nobody: uid = 65534, gid = 65534
>> creat09.c:62: TINFO: Found unused GID 3: SUCCESS (0)
>> creat09.c:93: TPASS: mntpoint/testdir/creat.tmp: Owned by correct group
>> creat09.c:97: TFAIL: mntpoint/testdir/creat.tmp: Setgid bit is set
>> creat09.c:93: TPASS: mntpoint/testdir/open.tmp: Owned by correct group
>> creat09.c:97: TFAIL: mntpoint/testdir/open.tmp: Setgid bit is set
>>
>> Thus clear the default umask.
>>
>> Signed-off-by: Petr Vorel<pvorel@suse.cz>
>> ---
>>    testcases/kernel/syscalls/creat/creat09.c | 2 ++
>>    1 file changed, 2 insertions(+)
>>
>> diff --git a/testcases/kernel/syscalls/creat/creat09.c b/testcases/kernel/syscalls/creat/creat09.c
>> index bed7bddb0e..70da7d2fc7 100644
>> --- a/testcases/kernel/syscalls/creat/creat09.c
>> +++ b/testcases/kernel/syscalls/creat/creat09.c
>> @@ -56,6 +56,8 @@ static void setup(void)
>>    		(int)ltpuser->pw_gid);
>>    	free_gid = tst_get_free_gid(ltpuser->pw_gid);
>>
>> +	umask(0);
>> +
>>    	/* Create directories and set permissions */
>>    	SAFE_MKDIR(WORKDIR, MODE_RWX);
>>    	SAFE_CHOWN(WORKDIR, ltpuser->pw_uid, free_gid);
>