netdev - Re: [PATCH net 1/4] bluetooth: Improve setsockopt() handling of malformed user input

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Message-ID: <CABBYNZL_awaZOKpsAyOaAbtnJLobJ1bQpF_9JNxpiyQg5P5q1Q@mail.gmail.com>
Date: Thu, 14 Nov 2024 21:50:04 -0500
From: Luiz Augusto von Dentz <luiz.dentz@...il.com>
To: David Wei <dw@...idwei.uk>
Cc: Michal Luczaj <mhal@...x.co>, Marcel Holtmann <marcel@...tmann.org>, 
	Johan Hedberg <johan.hedberg@...il.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	David Howells <dhowells@...hat.com>, Marc Dionne <marc.dionne@...istor.com>, 
	Luiz Augusto von Dentz <luiz.von.dentz@...el.com>, linux-bluetooth@...r.kernel.org, 
	netdev@...r.kernel.org, linux-afs@...ts.infradead.org, 
	Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH net 1/4] bluetooth: Improve setsockopt() handling of
 malformed user input

Hi David,

On Thu, Nov 14, 2024 at 9:30 PM David Wei <dw@...idwei.uk> wrote:
>
> On 2024-11-14 18:15, Luiz Augusto von Dentz wrote:
> > Hi David,
> >
> > On Thu, Nov 14, 2024 at 7:42 PM David Wei <dw@...idwei.uk> wrote:
> >>
> >> On 2024-11-14 15:27, Michal Luczaj wrote:
> >>> The bt_copy_from_sockptr() return value is being misinterpreted by most
> >>> users: a non-zero result is mistakenly assumed to represent an error code,
> >>> but actually indicates the number of bytes that could not be copied.
> >>>
> >>> Remove bt_copy_from_sockptr() and adapt callers to use
> >>> copy_safe_from_sockptr().
> >>>
> >>> For sco_sock_setsockopt() (case BT_CODEC) use copy_struct_from_sockptr() to
> >>> scrub parts of uninitialized buffer.
> >>>
> >>> Opportunistically, rename `len` to `optlen` in hci_sock_setsockopt_old()
> >>> and hci_sock_setsockopt().
> >>>
> >>> Fixes: 51eda36d33e4 ("Bluetooth: SCO: Fix not validating setsockopt user input")
> >>> Fixes: a97de7bff13b ("Bluetooth: RFCOMM: Fix not validating setsockopt user input")
> >>> Fixes: 4f3951242ace ("Bluetooth: L2CAP: Fix not validating setsockopt user input")
> >>> Fixes: 9e8742cdfc4b ("Bluetooth: ISO: Fix not validating setsockopt user input")
> >>> Fixes: b2186061d604 ("Bluetooth: hci_sock: Fix not validating setsockopt user input")
> >>> Signed-off-by: Michal Luczaj <mhal@...x.co>
> >>> ---
> >>>  include/net/bluetooth/bluetooth.h |  9 ---------
> >>>  net/bluetooth/hci_sock.c          | 14 +++++++-------
> >>>  net/bluetooth/iso.c               | 10 +++++-----
> >>>  net/bluetooth/l2cap_sock.c        | 20 +++++++++++---------
> >>>  net/bluetooth/rfcomm/sock.c       |  9 ++++-----
> >>>  net/bluetooth/sco.c               | 11 ++++++-----
> >>>  6 files changed, 33 insertions(+), 40 deletions(-)
> >>>
> >> ...
> >>> diff --git a/net/bluetooth/rfcomm/sock.c b/net/bluetooth/rfcomm/sock.c
> >>> index f48250e3f2e103c75d5937e1608e43c123aa3297..1001fb4cc21c0ecc7bcdd3ea9041770ede4f27b8 100644
> >>> --- a/net/bluetooth/rfcomm/sock.c
> >>> +++ b/net/bluetooth/rfcomm/sock.c
> >>> @@ -629,10 +629,9 @@ static int rfcomm_sock_setsockopt_old(struct socket *sock, int optname,
> >>>
> >>>       switch (optname) {
> >>>       case RFCOMM_LM:
> >>> -             if (bt_copy_from_sockptr(&opt, sizeof(opt), optval, optlen)) {
> >>> -                     err = -EFAULT;
> >>> +             err = copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen);
> >>> +             if (err)
> >>>                       break;
> >>> -             }
> >>
> >> This will return a positive integer if copy_safe_from_sockptr() fails.
> >
> > What are you talking about copy_safe_from_sockptr never returns a
> > positive value:
> >
> >  * Returns:
> >  *  * -EINVAL: @optlen < @ksize
> >  *  * -EFAULT: access to userspace failed.
> >  *  * 0 : @ksize bytes were copied
>
> Isn't this what this series is about? copy_from_sockptr() returns 0 on
> success, or a positive integer for number of bytes NOT copied on error.
> Patch 4 even updates the docs for copy_from_sockptr().
>
> copy_safe_from_sockptr()
>         -> copy_from_sockptr()
>         -> copy_from_sockptr_offset()
>         -> memcpy() for kernel to kernel OR
>         -> copy_from_user() otherwise

Well except the safe version does check what would otherwise cause a
positive return by the likes of copy_from_user and returns -EINVAL
instead, otherwise the documentation of copy_safe_from_sockptr is just
wrong and shall state that it could return positive as well but I
guess that would just make it as inconvenient so we might as well
detect when a positive value would be returned just return -EFAULT
instead.

> And copy_from_user() follows the same 0 for success or N > 0 for
> failure. It does not EFAULT on its own AFAIK.
>
> The docs for copy_safe_from_sockptr() that you've linked contains the
> exact misunderstanding that Michal is correcting.
>
> >
> >> Shouldn't this be:
> >>
> >> err = -EFAULT;
> >> if (copy_safe_from_sockptr(&opt, sizeof(opt), optval, optlen))
> >>         break;
> >
> >
> >



-- 
Luiz Augusto von Dentz