[Trusty] [PATCH 2/2] Bluetooth: Check L2CAP option sizes returned from l2cap_get_conf_opt
Kai Heng Feng
kai.heng.feng at canonical.com
Wed Feb 20 08:36:29 UTC 2019
> On Feb 20, 2019, at 9:16 AM, Tyler Hicks <tyhicks at canonical.com> wrote:
>
> On 2019-02-19 20:27:46, Kai-Heng Feng wrote:
>> From: Marcel Holtmann <marcel at holtmann.org>
>>
>> When doing option parsing for standard type values of 1, 2 or 4 octets,
>> the value is converted directly into a variable instead of a pointer. To
>> avoid being tricked into being a pointer, check that for these option
>> types that sizes actually match. In L2CAP every option is fixed size and
>> thus it is prudent anyway to ensure that the remote side sends us the
>> right option size along with option paramters.
>>
>> If the option size is not matching the option type, then that option is
>> silently ignored. It is a protocol violation and instead of trying to
>> give the remote attacker any further hints just pretend that option is
>> not present and proceed with the default values. Implementation
>> following the specification and its qualification procedures will always
>> use the correct size and thus not being impacted here.
>>
>> To keep the code readable and consistent accross all options, a few
>> cosmetic changes were also required.
>>
>> CVE-2019-3460
>>
>> Signed-off-by: Marcel Holtmann <marcel at holtmann.org>
>> Reviewed-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
>> Signed-off-by: Johan Hedberg <johan.hedberg at intel.com>
>> (backported from commit af3d5d1c87664a4f150fcf3534c6567cb19909b0 linux-next)
>
> Could you give a little info about what kind of backporting effort this
> required? I quickly compared this patch to the upstream patch and it
> mostly looked like contextual changes but I'd like for you to confirm
> that.
Yes, it’s just contextual change.
>
> Best practice would be to leave a little comment above your
> Signed-off-by line. You're probably already aware of this but here's the
> in-tree documentation on this practice:
I’ve never added bracket comments in the past, but this is a good practice.
I’ll do this in the future.
Do you want me to re-send a V2?
Kai-Heng
>
> If you are a subsystem or branch maintainer, sometimes you need to
> slightly modify patches you receive in order to merge them, because the
> code is not exactly the same in your tree and the submitters’. If you
> stick strictly to rule (c), you should ask the submitter to rediff, but
> this is a totally counter-productive waste of time and energy. Rule (b)
> allows you to adjust the code, but then it is very impolite to change
> one submitter’s code and make him endorse your bugs. To solve this
> problem, it is recommended that you add a line between the last
> Signed-off-by header and yours, indicating the nature of your changes.
> While there is nothing mandatory about this, it seems like prepending
> the description with your mail and/or name, all enclosed in square
> brackets, is noticeable enough to make it obvious that you are
> responsible for last-minute changes. Example:
>
> Signed-off-by: Random J Developer <random at developer.example.org>
> [lucky at maintainer.example.org: struct foo moved from foo.c to foo.h]
> Signed-off-by: Lucky K Maintainer <lucky at maintainer.example.org>
>
> This practice is particularly helpful if you maintain a stable branch
> and want at the same time to credit the author, track changes, merge the
> fix, and protect the submitter from complaints. Note that under no
> circumstances can you change the author’s identity (the From header), as
> it is the one which appears in the changelog.
>
> - https://www.kernel.org/doc/html/latest/process/submitting-patches.html
>
> Tyler
>
>> Signed-off-by: Kai-Heng Feng <kai.heng.feng at canonical.com>
>> ---
>> net/bluetooth/l2cap_core.c | 77 +++++++++++++++++++++++---------------
>> 1 file changed, 46 insertions(+), 31 deletions(-)
>>
>> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
>> index 61d0f290c0c6..a7de6cbdeced 100644
>> --- a/net/bluetooth/l2cap_core.c
>> +++ b/net/bluetooth/l2cap_core.c
>> @@ -3284,10 +3284,14 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>>
>> switch (type) {
>> case L2CAP_CONF_MTU:
>> + if (olen != 2)
>> + break;
>> mtu = val;
>> break;
>>
>> case L2CAP_CONF_FLUSH_TO:
>> + if (olen != 2)
>> + break;
>> chan->flush_to = val;
>> break;
>>
>> @@ -3295,26 +3299,30 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>> break;
>>
>> case L2CAP_CONF_RFC:
>> - if (olen == sizeof(rfc))
>> - memcpy(&rfc, (void *) val, olen);
>> + if (olen != sizeof(rfc))
>> + break;
>> + memcpy(&rfc, (void *) val, olen);
>> break;
>>
>> case L2CAP_CONF_FCS:
>> + if (olen != 1)
>> + break;
>> if (val == L2CAP_FCS_NONE)
>> set_bit(CONF_RECV_NO_FCS, &chan->conf_state);
>> break;
>>
>> case L2CAP_CONF_EFS:
>> - if (olen == sizeof(efs)) {
>> - remote_efs = 1;
>> - memcpy(&efs, (void *) val, olen);
>> - }
>> + if (olen != sizeof(efs))
>> + break;
>> + remote_efs = 1;
>> + memcpy(&efs, (void *) val, olen);
>> break;
>>
>> case L2CAP_CONF_EWS:
>> + if (olen != 2)
>> + break;
>> if (!chan->conn->hs_enabled)
>> return -ECONNREFUSED;
>> -
>> set_bit(FLAG_EXT_CTRL, &chan->flags);
>> set_bit(CONF_EWS_RECV, &chan->conf_state);
>> chan->tx_win_max = L2CAP_DEFAULT_EXT_WINDOW;
>> @@ -3324,7 +3332,6 @@ static int l2cap_parse_conf_req(struct l2cap_chan *chan, void *data, size_t data
>> default:
>> if (hint)
>> break;
>> -
>> result = L2CAP_CONF_UNKNOWN;
>> *((u8 *) ptr++) = type;
>> break;
>> @@ -3492,55 +3499,60 @@ static int l2cap_parse_conf_rsp(struct l2cap_chan *chan, void *rsp, int len,
>>
>> switch (type) {
>> case L2CAP_CONF_MTU:
>> + if (olen != 2)
>> + break;
>> if (val < L2CAP_DEFAULT_MIN_MTU) {
>> *result = L2CAP_CONF_UNACCEPT;
>> chan->imtu = L2CAP_DEFAULT_MIN_MTU;
>> } else
>> chan->imtu = val;
>> - l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu, endptr - ptr);
>> + l2cap_add_conf_opt(&ptr, L2CAP_CONF_MTU, 2, chan->imtu,
>> + endptr - ptr);
>> break;
>>
>> case L2CAP_CONF_FLUSH_TO:
>> + if (olen != 2)
>> + break;
>> chan->flush_to = val;
>> - l2cap_add_conf_opt(&ptr, L2CAP_CONF_FLUSH_TO,
>> - 2, chan->flush_to, endptr - ptr);
>> + l2cap_add_conf_opt(&ptr, L2CAP_CONF_FLUSH_TO, 2,
>> + chan->flush_to, endptr - ptr);
>> break;
>>
>> case L2CAP_CONF_RFC:
>> - if (olen == sizeof(rfc))
>> - memcpy(&rfc, (void *)val, olen);
>> -
>> + if (olen != sizeof(rfc))
>> + break;
>> + memcpy(&rfc, (void *)val, olen);
>> if (test_bit(CONF_STATE2_DEVICE, &chan->conf_state) &&
>> rfc.mode != chan->mode)
>> return -ECONNREFUSED;
>> -
>> chan->fcs = 0;
>> -
>> - l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC,
>> - sizeof(rfc), (unsigned long) &rfc, endptr - ptr);
>> + l2cap_add_conf_opt(&ptr, L2CAP_CONF_RFC, sizeof(rfc),
>> + (unsigned long) &rfc, endptr - ptr);
>> break;
>>
>> case L2CAP_CONF_EWS:
>> + if (olen != 2)
>> + break;
>> chan->ack_win = min_t(u16, val, chan->ack_win);
>> l2cap_add_conf_opt(&ptr, L2CAP_CONF_EWS, 2,
>> chan->tx_win, endptr - ptr);
>> break;
>>
>> case L2CAP_CONF_EFS:
>> - if (olen == sizeof(efs)) {
>> - memcpy(&efs, (void *)val, olen);
>> -
>> - if (chan->local_stype != L2CAP_SERV_NOTRAFIC &&
>> - efs.stype != L2CAP_SERV_NOTRAFIC &&
>> - efs.stype != chan->local_stype)
>> - return -ECONNREFUSED;
>> -
>> - l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs),
>> - (unsigned long) &efs, endptr - ptr);
>> - }
>> + if (olen != sizeof(efs))
>> + break;
>> + memcpy(&efs, (void *)val, olen);
>> + if (chan->local_stype != L2CAP_SERV_NOTRAFIC &&
>> + efs.stype != L2CAP_SERV_NOTRAFIC &&
>> + efs.stype != chan->local_stype)
>> + return -ECONNREFUSED;
>> + l2cap_add_conf_opt(&ptr, L2CAP_CONF_EFS, sizeof(efs),
>> + (unsigned long) &efs, endptr - ptr);
>> break;
>>
>> case L2CAP_CONF_FCS:
>> + if (olen != 1)
>> + break;
>> if (*result == L2CAP_CONF_PENDING)
>> if (val == L2CAP_FCS_NONE)
>> set_bit(CONF_RECV_NO_FCS,
>> @@ -3655,10 +3667,13 @@ static void l2cap_conf_rfc_get(struct l2cap_chan *chan, void *rsp, int len)
>>
>> switch (type) {
>> case L2CAP_CONF_RFC:
>> - if (olen == sizeof(rfc))
>> - memcpy(&rfc, (void *)val, olen);
>> + if (olen != sizeof(rfc))
>> + break;
>> + memcpy(&rfc, (void *)val, olen);
>> break;
>> case L2CAP_CONF_EWS:
>> + if (olen != 2)
>> + break;
>> txwin_ext = val;
>> break;
>> }
>> --
>> 2.17.1
>>
>>
>> --
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