Re: [PATCH] idmapped-mounts: probe O_TMPFILE support with the caller's mapped id

在 2026/8/11 4:40, Zorro Lang 写道:
> On Thu, Aug 06, 2026 at 02:11:55PM +0800, Zizhi Wo wrote:
>> friendly ping...
> 
> Hi Zizhi, actually I'm waiting for the fix from vfs list.

Sorry, I hadn't noticed that this issue had already been discussed and
fixed by the community. Thanks for pointing it out.

Thanks,
Zizhi Wo

> 
> Hi Christian,
> 
> Could you please take a look at this issue? Quite a few people have submitted
> patches trying to fix this test issue. Given that you are the authority on
> this topic and previously sent a patchset [1] to fix this kind of issue, I think
> accepting your patch would be the best approach to stay aligned with upstream
> VFS. Christoph also metioned that [2] last time. I don't want to make this issue
> fixing any more complicated. Could you please provide your review point or
> rebase your fix on the latest fstests for-next branch, we'll review it ASAP.
> 
> [1]
> https://lore.kernel.org/fstests/[email protected]/
> 
> [2]
> https://lore.kernel.org/fstests/[email protected]/
> 
> Thanks,
> Zorro
> 
>>
>> 在 2026/7/31 17:02, Zizhi Wo 写道:
>>> From: Zizhi Wo <[email protected]>
>>>
>>> Kernel commit 539dce114465 ("fs: refuse O_TMPFILE creation with an
>>> unmapped fsuid or fsgid") made vfs_tmpfile() return -EOVERFLOW when the
>>> caller's fsuid/fsgid has no mapping in the filesystem's user namespace
>>> after applying the mount's idmapping. This is a no-op on non-idmapped
>>> mounts and only takes effect on an idmapped mount that does not map the
>>> caller.
>>>
>>> The idmapped-mount testcases behind generic/696 and generic/697 build an
>>> idmapping (e.g. "0 10000 10000") that covers host uid 10000-19999 but
>>> not uid 0, then call openat_tmpfile_supported() from the parent process
>>> that is still real root (fsuid 0). The probe now gets -EOVERFLOW, falls
>>> into the log_errno() branch, and prints
>>>
>>>     utils.c: 928: openat_tmpfile_supported - Value too large for defined \
>>> data type - failure: create
>>>
>>> to stderr. Both testcases expect "Silence is golden", so this spurious
>>> output fails them, even though the kernel behavior is correct and the
>>> testcases' own assertions all pass.
>>>
>>> Move each openat_tmpfile_supported() call into the child, after
>>> switch_ids()/switch_userns(), so it probes with the mapped identity the
>>> tmpfile section uses. Silencing EOVERFLOW in openat_tmpfile_supported()
>>> would make it indistinguishable whether the idmapping genuinely has no
>>> mapping for any caller, or the probe just ran in the unmapped parent before
>>> the switch.
>>>
>>> Signed-off-by: Zizhi Wo <[email protected]>
>>> ---
>>>    src/vfs/idmapped-mounts.c | 32 ++++++++++++++++++++------------
>>>    1 file changed, 20 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/src/vfs/idmapped-mounts.c b/src/vfs/idmapped-mounts.c
>>> index ed9992f9..bfbe9042 100644
>>> --- a/src/vfs/idmapped-mounts.c
>>> +++ b/src/vfs/idmapped-mounts.c
>>> @@ -3838,8 +3838,6 @@ int tcore_setgid_create_idmapped(const struct vfstest_info *info)
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	pid = fork();
>>>    	if (pid < 0) {
>>>    		log_stderr("failure: fork");
>>> @@ -3849,6 +3847,8 @@ int tcore_setgid_create_idmapped(const struct vfstest_info *info)
>>>    		if (!switch_ids(10000, 11000))
>>>    			die("failure: switch fsids");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		/* create regular file via open() */
>>>    		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
>>>    		if (file1_fd < 0)
>>> @@ -4014,8 +4014,6 @@ int tcore_setgid_create_idmapped_in_userns(const struct vfstest_info *info)
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	pid = fork();
>>>    	if (pid < 0) {
>>>    		log_stderr("failure: fork");
>>> @@ -4025,6 +4023,8 @@ int tcore_setgid_create_idmapped_in_userns(const struct vfstest_info *info)
>>>    		if (!switch_userns(attr.userns_fd, 0, 0, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		/* create regular file via open() */
>>>    		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
>>>    		if (file1_fd < 0)
>>> @@ -4133,6 +4133,8 @@ int tcore_setgid_create_idmapped_in_userns(const struct vfstest_info *info)
>>>    		if (!switch_userns(attr.userns_fd, 0, 0, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		if (!caps_down_fsetid())
>>>    			die("failure: caps_down_fsetid");
>>> @@ -4257,6 +4259,8 @@ int tcore_setgid_create_idmapped_in_userns(const struct vfstest_info *info)
>>>    		if (!switch_userns(attr.userns_fd, 0, 1000, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		if (!caps_down_fsetid())
>>>    			die("failure: caps_down_fsetid");
>>> @@ -7733,8 +7737,6 @@ static int setgid_create_umask_idmapped(const struct vfstest_info *info)
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	pid = fork();
>>>    	if (pid < 0) {
>>>    		log_stderr("failure: fork");
>>> @@ -7752,6 +7754,8 @@ static int setgid_create_umask_idmapped(const struct vfstest_info *info)
>>>    		if (!switch_ids(10000, 11000))
>>>    			die("failure: switch fsids");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		/* create regular file via open() */
>>>    		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
>>>    		if (file1_fd < 0)
>>> @@ -7947,8 +7951,6 @@ static int setgid_create_umask_idmapped_in_userns(const struct vfstest_info *inf
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	/*
>>>    	 * Below we verify that setgid inheritance for a newly created file or
>>>    	 * directory works correctly. As part of this we need to verify that
>>> @@ -7984,6 +7986,8 @@ static int setgid_create_umask_idmapped_in_userns(const struct vfstest_info *inf
>>>    		if (!switch_userns(attr.userns_fd, 0, 0, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		if (!caps_down_fsetid())
>>>    			die("failure: caps_down_fsetid");
>>> @@ -8181,8 +8185,6 @@ static int setgid_create_acl_idmapped(const struct vfstest_info *info)
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	pid = fork();
>>>    	if (pid < 0) {
>>>    		log_stderr("failure: fork");
>>> @@ -8207,6 +8209,8 @@ static int setgid_create_acl_idmapped(const struct vfstest_info *info)
>>>    		if (!switch_ids(10000, 11000))
>>>    			die("failure: switch fsids");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		/* create regular file via open() */
>>>    		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
>>>    		if (file1_fd < 0)
>>> @@ -8342,6 +8346,8 @@ static int setgid_create_acl_idmapped(const struct vfstest_info *info)
>>>    		if (!switch_ids(10000, 11000))
>>>    			die("failure: switch fsids");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		/* create regular file via open() */
>>>    		file1_fd = openat(open_tree_fd, FILE1, O_CREAT | O_EXCL | O_CLOEXEC, S_IXGRP | S_ISGID);
>>>    		if (file1_fd < 0)
>>> @@ -8536,8 +8542,6 @@ static int setgid_create_acl_idmapped_in_userns(const struct vfstest_info *info)
>>>    		goto out;
>>>    	}
>>> -	supported = openat_tmpfile_supported(open_tree_fd);
>>> -
>>>    	/*
>>>    	 * Below we verify that setgid inheritance for a newly created file or
>>>    	 * directory works correctly. As part of this we need to verify that
>>> @@ -8580,6 +8584,8 @@ static int setgid_create_acl_idmapped_in_userns(const struct vfstest_info *info)
>>>    		if (!switch_userns(attr.userns_fd, 0, 0, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		if (!caps_down_fsetid())
>>>    			die("failure: caps_down_fsetid");
>>> @@ -8723,6 +8729,8 @@ static int setgid_create_acl_idmapped_in_userns(const struct vfstest_info *info)
>>>    		if (!switch_userns(attr.userns_fd, 0, 0, false))
>>>    			die("failure: switch_userns");
>>> +		supported = openat_tmpfile_supported(open_tree_fd);
>>> +
>>>    		if (!caps_down_fsetid())
>>>    			die("failure: caps_down_fsetid");
>>
>