Re: [PATCH for-5.7] splice: move f_mode checks to do_{splice,tee}()

[Pavel Begunkov <asml.silence@gmail.com>]

On 06/05/2020 00:10, Clay Harris wrote:
> On Mon, May 04 2020 at 22:39:35 +0300, Pavel Begunkov quoth thus:
> 
>> do_splice() is used by io_uring, as will be do_tee(). Move f_mode
>> checks from sys_{splice,tee}() to do_{splice,tee}(), so they're
>> enforced for io_uring as well.
> 
> I'm not seeing any check against splicing a pipe to itself in the
> io_uring path, although maybe I just missed it.  As the comment
> below says: /* Splicing to self would be fun, but... */ .

io_uring just forwards a request to do_splice(), which do the check at the exact
place you mentioned. The similar story is with do_tee().

> 
>> Fixes: 7d67af2c0134 ("io_uring: add splice(2) support")
>> Reported-by: Jann Horn <jannh@google.com>
>> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
>> ---
>>  fs/splice.c | 45 ++++++++++++++++++---------------------------
>>  1 file changed, 18 insertions(+), 27 deletions(-)
>>
>> diff --git a/fs/splice.c b/fs/splice.c
>> index 4735defc46ee..fd0a1e7e5959 100644
>> --- a/fs/splice.c
>> +++ b/fs/splice.c
>> @@ -1118,6 +1118,10 @@ long do_splice(struct file *in, loff_t __user *off_in,
>>  	loff_t offset;
>>  	long ret;
>>  
>> +	if (unlikely(!(in->f_mode & FMODE_READ) ||
>> +		     !(out->f_mode & FMODE_WRITE)))
>> +		return -EBADF;
>> +
>>  	ipipe = get_pipe_info(in);
>>  	opipe = get_pipe_info(out);
>>  
>> @@ -1125,12 +1129,6 @@ long do_splice(struct file *in, loff_t __user *off_in,
>>  		if (off_in || off_out)
>>  			return -ESPIPE;
>>  
>> -		if (!(in->f_mode & FMODE_READ))
>> -			return -EBADF;
>> -
>> -		if (!(out->f_mode & FMODE_WRITE))
>> -			return -EBADF;
>> -
>>  		/* Splicing to self would be fun, but... */
>>  		if (ipipe == opipe)
>>  			return -EINVAL;
>> @@ -1153,9 +1151,6 @@ long do_splice(struct file *in, loff_t __user *off_in,
>>  			offset = out->f_pos;
>>  		}
>>  
>> -		if (unlikely(!(out->f_mode & FMODE_WRITE)))
>> -			return -EBADF;
>> -
>>  		if (unlikely(out->f_flags & O_APPEND))
>>  			return -EINVAL;
>>  
>> @@ -1440,15 +1435,11 @@ SYSCALL_DEFINE6(splice, int, fd_in, loff_t __user *, off_in,
>>  	error = -EBADF;
>>  	in = fdget(fd_in);
>>  	if (in.file) {
>> -		if (in.file->f_mode & FMODE_READ) {
>> -			out = fdget(fd_out);
>> -			if (out.file) {
>> -				if (out.file->f_mode & FMODE_WRITE)
>> -					error = do_splice(in.file, off_in,
>> -							  out.file, off_out,
>> -							  len, flags);
>> -				fdput(out);
>> -			}
>> +		out = fdget(fd_out);
>> +		if (out.file) {
>> +			error = do_splice(in.file, off_in, out.file, off_out,
>> +					  len, flags);
>> +			fdput(out);
>>  		}
>>  		fdput(in);
>>  	}
>> @@ -1770,6 +1761,10 @@ static long do_tee(struct file *in, struct file *out, size_t len,
>>  	struct pipe_inode_info *opipe = get_pipe_info(out);
>>  	int ret = -EINVAL;
>>  
>> +	if (unlikely(!(in->f_mode & FMODE_READ) ||
>> +		     !(out->f_mode & FMODE_WRITE)))
>> +		return -EBADF;
>> +
>>  	/*
>>  	 * Duplicate the contents of ipipe to opipe without actually
>>  	 * copying the data.
>> @@ -1795,7 +1790,7 @@ static long do_tee(struct file *in, struct file *out, size_t len,
>>  
>>  SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
>>  {
>> -	struct fd in;
>> +	struct fd in, out;
>>  	int error;
>>  
>>  	if (unlikely(flags & ~SPLICE_F_ALL))
>> @@ -1807,14 +1802,10 @@ SYSCALL_DEFINE4(tee, int, fdin, int, fdout, size_t, len, unsigned int, flags)
>>  	error = -EBADF;
>>  	in = fdget(fdin);
>>  	if (in.file) {
>> -		if (in.file->f_mode & FMODE_READ) {
>> -			struct fd out = fdget(fdout);
>> -			if (out.file) {
>> -				if (out.file->f_mode & FMODE_WRITE)
>> -					error = do_tee(in.file, out.file,
>> -							len, flags);
>> -				fdput(out);
>> -			}
>> +		out = fdget(fdout);
>> +		if (out.file) {
>> +			error = do_tee(in.file, out.file, len, flags);
>> +			fdput(out);
>>  		}
>>   		fdput(in);
>>   	}
>> -- 
>> 2.24.0

-- 
Pavel Begunkov