On 26/09/20 1:16 pm, Marcel Holtmann wrote: > Hi Anant, > >> When the amount of data stored in the location corresponding to >> iov_iter *from is less then 4, some data seems to go uninitialized. >> >> Updating this condition accordingly, makes sense both intuitively and >> logically as well, since the other check for extreme condition done is if >> len > HCI_MAX_FRAME_SIZE, which is HCI_MAX_ACL_SIZE (which is 1024) + 4; >> which itself gives some idea about what must be the ideal mininum size. >> >> Reported-and-tested by: syzbot+4c14a8f574461e1c3659@xxxxxxxxxxxxxxxxxxxxxxxxx >> Signed-off-by: Anant Thazhemadam <anant.thazhemadam@xxxxxxxxx> >> --- >> If there is some explicit reason why len < 4 doesn't work, and only len < 2 works, >> please do let me know. >> The commit message that introduced the initial change >> (512b2268156a4e15ebf897f9a883bdee153a54b7) wasn't exactly very helpful in this >> respect, and I couldn't find a whole lot of discussion regarding this either. >> >> drivers/bluetooth/hci_vhci.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/drivers/bluetooth/hci_vhci.c b/drivers/bluetooth/hci_vhci.c >> index 8ab26dec5f6e..0c49821d7b98 100644 >> --- a/drivers/bluetooth/hci_vhci.c >> +++ b/drivers/bluetooth/hci_vhci.c >> @@ -159,7 +159,7 @@ static inline ssize_t vhci_get_user(struct vhci_data *data, >> __u8 pkt_type, opcode; >> int ret; >> >> - if (len < 2 || len > HCI_MAX_FRAME_SIZE) >> + if (len < 4 || len > HCI_MAX_FRAME_SIZE) >> return -EINVAL; > so the minimum requirement is to have an 1 octet packet indicator. If some other functions are missing length checks, then it should be fixed there. I see that in case of HCI_VENDOR_PKT we need to check for the 2nd octet to be present, but I have no idea why you require 3 octets minimum. As I said, if so, then the other functions that get called require proper range checks. > > Regards > > Marcel Ah, I see. That makes sense, and I'm sorry for this. I just thought since HCI_MAX_FRAME_SIZE was 4 more than 1024, min. len might have to be 4. Taking a look at the reproducer, it becomes evident that the only reason this patch didn't trigger an issue was because the reproducer ran with len = 3. I don't really have a strong enough clue yet about where things are going wrong, so I'd appreciate any guidance/insight into this, and where I should be looking. :/ Also, although the bug says it is only an uninit-value, it eventually ends up triggering a kernel panic (looking at a log rather than a report shows that as well). Thanks, Anant
