Commit a6b87bfc authored by Alan Stern's avatar Alan Stern Committed by Benjamin Tissoires
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HID: core: Harden s32ton() against conversion to 0 bits 



Testing by the syzbot fuzzer showed that the HID core gets a
shift-out-of-bounds exception when it tries to convert a 32-bit
quantity to a 0-bit quantity.  Ideally this should never occur, but
there are buggy devices and some might have a report field with size
set to zero; we shouldn't reject the report or the device just because
of that.

Instead, harden the s32ton() routine so that it returns a reasonable
result instead of crashing when it is called with the number of bits
set to 0 -- the same as what snto32() does.

Signed-off-by: default avatarAlan Stern <stern@rowland.harvard.edu>
Reported-by: default avatar <syzbot+b63d677d63bcac06cf90@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/linux-usb/68753a08.050a0220.33d347.0008.GAE@google.com/


Tested-by: default avatar <syzbot+b63d677d63bcac06cf90@syzkaller.appspotmail.com>
Fixes: dde5845a ("[PATCH] Generic HID layer - code split")
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/613a66cd-4309-4bce-a4f7-2905f9bce0c9@rowland.harvard.edu


Signed-off-by: default avatarBenjamin Tissoires <bentiss@kernel.org>
parent 12f33ef6

drivers/hid/hid-core.c

+5 −1
Original line number Diff line number Diff line
@@ -66,8 +66,12 @@ static s32 snto32(__u32 value, unsigned int n) 


static u32 s32ton(__s32 value, unsigned int n)

{

	s32 a = value >> (n - 1);

	s32 a;



	if (!value || !n)

		return 0;



	a = value >> (n - 1);

	if (a && a != -1)

		return value < 0 ? 1 << (n - 1) : (1 << (n - 1)) - 1;

	return value & ((1 << n) - 1);