Re: [PATCH 6.1.y] HID: core: Harden s32ton() against conversion to 0 bits

Re: [PATCH 6.1.y] HID: core: Harden s32ton() against conversion to 0 bits

[syzbot]

> #syz test: 

This bug is already marked as fixed. No point in testing.

> git://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git linux-6.1.y
>
> drivers/hid/hid-core.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index ed65523d77c2..c8cca0c7ec67 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -1354,7 +1354,12 @@ EXPORT_SYMBOL_GPL(hid_snto32);
>
>   static u32 s32ton(__s32 value, unsigned 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);
> -- 
> 2.43.0
>
>

[PATCH 6.1.y] HID: core: Harden s32ton() against conversion to 0 bits

[jetlan9]

From: Alan Stern <stern@rowland.harvard.edu>

[ Upstream commit a6b87bfc2ab5bccb7ad953693c85d9062aef3fdd ]

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: Alan Stern <stern@rowland.harvard.edu>
Reported-by: syzbot+b63d677d63bcac06cf90@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/linux-usb/68753a08.050a0220.33d347.0008.GAE@google.com/
Tested-by: syzbot+b63d677d63bcac06cf90@syzkaller.appspotmail.com
Fixes: dde5845a529f ("[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: Benjamin Tissoires <bentiss@kernel.org>
[ s32ton() was moved by c653ffc28340 ("HID: stop exporting hid_snto32()").
  Minor context change fixed. ]
Signed-off-by: Wenshan Lan <jetlan9@163.com>
---
 drivers/hid/hid-core.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index ed65523d77c2..c8cca0c7ec67 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1354,7 +1354,12 @@ EXPORT_SYMBOL_GPL(hid_snto32);
 
 static u32 s32ton(__s32 value, unsigned 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);
-- 
2.43.0