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Subject: Re: [PATCH v2 2/2] fs: avoid fdput() after failed fdget() in
 kernel_read_file_from_fd()
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     axboe@kernel.dk, zohar@linux.vnet.ibm.com, mcgrof@kernel.org,
        keescook@chromium.org, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org,
        Shuah Khan <skhan@linuxfoundation.org>
References: <cover.1589311577.git.skhan@linuxfoundation.org>
 <1159d74f88d100521c568037327ebc8ec7ffc6ef.1589311577.git.skhan@linuxfoundation.org>
 <20200513054950.GT23230@ZenIV.linux.org.uk>
From:   Shuah Khan <skhan@linuxfoundation.org>
Message-ID: <19709a34-68be-abb2-a8e1-f42e37a103ee@linuxfoundation.org>
Date:   Wed, 13 May 2020 11:56:11 -0600
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On 5/12/20 11:49 PM, Al Viro wrote:
> On Tue, May 12, 2020 at 01:43:05PM -0600, Shuah Khan wrote:
>> Fix kernel_read_file_from_fd() to avoid fdput() after a failed fdget().
>> fdput() doesn't do fput() on this file since FDPUT_FPUT isn't set
>> in fd.flags. Fix it anyway since failed fdget() doesn't require
>> a fdput().
>>
>> This was introduced in a commit that added kernel_read_file_from_fd() as
>> a wrapper for the VFS common kernel_read_file().
>>
>> Fixes: b844f0ecbc56 ("vfs: define kernel_copy_file_from_fd()")
>> Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>
>> ---
>>   fs/exec.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/exec.c b/fs/exec.c
>> index 06b4c550af5d..ea24bdce939d 100644
>> --- a/fs/exec.c
>> +++ b/fs/exec.c
>> @@ -1021,8 +1021,8 @@ int kernel_read_file_from_fd(int fd, void **buf, loff_t *size, loff_t max_size,
>>   		goto out;
>>   
>>   	ret = kernel_read_file(f.file, buf, size, max_size, id);
>> -out:
>>   	fdput(f);
>> +out:
>>   	return ret;
> 
> Again, that goto is a pointless obfuscation; just return -EBADF
> and be done with that.
> 

My reasoning is if this routine ends up growing it might be useful
to handle the return this way.

In any case, I will send v3 for both of these patches.

thanks,
-- Shuah