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From: Richard Sailer <>
To: kernelnewbies <>
Subject: Dubios pointer casting with put_user()
Date: Fri, 17 Jul 2020 02:13:34 +0200
Message-ID: <> (raw)

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In the following example from net/dccp/proto.c the pointer given
put_user() is casted to (int __user *) although the value to copy is a
unsigned long. Is this (correctness and security wise) sane? Because as
I understand it put_user() determines the amount it copies from the
pointer type.

		unsigned long amount = 0;

		skb = skb_peek(&sk->sk_receive_queue);
		if (skb != NULL) {
			amount = skb->len;
		rc = put_user(amount, (int __user *)arg);

Also skb->len is an unsigned int realisticly in most cases < 9000 (and
in all cases I can imagine < int_max (with 16 bit)).

I would like to declare amount as int outside of the switch case
statement (because I  need it in another case statement as signed int)
would it be safe to do so?

-- Richard

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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17  0:13 Richard Sailer [this message]
2020-07-17  0:19 ` Richard Sailer
2020-07-17 22:46 ` Valdis Klētnieks
2020-07-19 12:15   ` Richard Sailer
2020-07-19 22:50     ` Valdis Klētnieks

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