Date: Sun, 5 Nov 2023 18:36:52 +0100 From: Solar Designer <solar@...nwall.com> To: Pietro Borrello <borrello@...g.uniroma1.it> Cc: oss-security@...ts.openwall.com Subject: Re: Linux Kernel: hid: type confusions on hid report_list entry On Tue, Jan 17, 2023 at 06:05:30PM +0100, Pietro Borrello wrote: > We found potential misuses of list_entry() on lists in hid driver > code that are not checked, specifically hid_validate_values() in > drivers/hid/hid-core.c and bigben_probe() in drivers/hid/hid-bigbenff.c. > Issuing a list_entry() on an empty list causes a type confusion making > the list_entry point to the list_head itself. > The most impactful seems the missing check for an empty list in > hid_validate_values() which is supposed to check the validity of the > reports themselves, potentially affecting all the drivers that rely on it. > > The problem is caused by the driver's assumption that the device must > have a valid report_list. While this will be true for all normal HID > devices, a suitably malicious device can violate the assumption. > > At a first glance, it may seem that the patches have security implications. > However, when plugging a device which provides a descriptor with no output > report, the type confusions will create a fake struct hid_report* > which points to ((struct hid_device *)hid).report_enum[type].report_list. > This, by chance, makes the type confused structure to span > the `struct hid_report* report_id_hash` array in the > ((struct hid_device *)hid).report_enum[type] field. > > Then, due to their semantics hid_validate_values() will check > (report->maxfield > field_index) on the type-confused report, > and the maxfield field happens to overlap on the > report_id_hash array in the report_enum[type] field > which are all NULL since we provided no reports. > Similarly, for bigben_probe(), the confused report entry is > used in the bigben_worker() function which checks > (report->field != NULL) that, again, overlaps with a NULL > pointer. > It seems there is a commit (918aa1ef104d: "HID: bigbenff: prevent > null pointer dereference") which added the check for report_field > being NULL to bigben_worker() to prevent crashing, but without > checking the actual root cause. > > Thus, while being type confusions bugs, they are not exploitable. > The list checks should be added also to prevent future exploitability > if the shape of the structure changes (e.g., structure layout > randomization), and they do not overlap anymore with NULL pointers. > In this case, it is not exploitable just by the pure chance of struct > member ordering. > > This post has been written in accordance with linux-distros rules to > which we disclosed the initial findings of the potential vulnerabilities. > as even if the bugs seem not exploitable, the wider community on > oss-security might see how the issue does have security relevance. > > We submitted patches to fix the issue by checking that the lists > are non-empty before allowing them to be used: > https://email@example.com/T/ This was assigned CVE-2023-1073, which also covers a bug mentioned in another oss-security posting below: CVE-2023-1073 - Type Confusion in hid_validate_values() patch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=b12fece4c64857e5fab4290bf01b2e0317a88456 oss-security: https://www.openwall.com/lists/oss-security/2023/01/17/3 CVE-2023-1073 - Type Confusion in bigben_probe() patch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=c7bf714f875531f227f2ef1fdcc8f4d44e7c7d9d oss-security: https://www.openwall.com/lists/oss-security/2023/01/17/3 CVE-2023-1073 - NULL Ptr Deref in betopff_init() patch: https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=3782c0d6edf658b71354a64d60aa7a296188fc90 oss-security: https://www.openwall.com/lists/oss-security/2023/01/18/3 Alexander
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