Patch "HID: hyperv: avoid struct memcpy overrun warning" has been added to the 6.4-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    HID: hyperv: avoid struct memcpy overrun warning

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     hid-hyperv-avoid-struct-memcpy-overrun-warning.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit b4bc4dd1ce538c2050276f4c029b3d91ea87604f
Author: Arnd Bergmann <arnd@xxxxxxxx>
Date:   Wed Jul 5 16:02:24 2023 +0200

    HID: hyperv: avoid struct memcpy overrun warning
    
    [ Upstream commit 5f151364b1da6bd217632fd4ee8cc24eaf66a497 ]
    
    A previous patch addressed the fortified memcpy warning for most
    builds, but I still see this one with gcc-9:
    
    In file included from include/linux/string.h:254,
                     from drivers/hid/hid-hyperv.c:8:
    In function 'fortify_memcpy_chk',
        inlined from 'mousevsc_on_receive' at drivers/hid/hid-hyperv.c:272:3:
    include/linux/fortify-string.h:583:4: error: call to '__write_overflow_field' declared with attribute warning: detected write beyond size of field (1st parameter); maybe use struct_group()? [-Werror=attribute-warning]
      583 |    __write_overflow_field(p_size_field, size);
          |    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    
    My guess is that the WARN_ON() itself is what confuses gcc, so it no
    longer sees that there is a correct range check. Rework the code in a
    way that helps readability and avoids the warning.
    
    Fixes: 542f25a94471 ("HID: hyperv: Replace one-element array with flexible-array member")
    Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
    Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
    Link: https://lore.kernel.org/r/20230705140242.844167-1-arnd@xxxxxxxxxx
    Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/hid/hid-hyperv.c b/drivers/hid/hid-hyperv.c
index 49d4a26895e76..f33485d83d24f 100644
--- a/drivers/hid/hid-hyperv.c
+++ b/drivers/hid/hid-hyperv.c
@@ -258,19 +258,17 @@ static void mousevsc_on_receive(struct hv_device *device,
 
 	switch (hid_msg_hdr->type) {
 	case SYNTH_HID_PROTOCOL_RESPONSE:
+		len = struct_size(pipe_msg, data, pipe_msg->size);
+
 		/*
 		 * While it will be impossible for us to protect against
 		 * malicious/buggy hypervisor/host, add a check here to
 		 * ensure we don't corrupt memory.
 		 */
-		if (struct_size(pipe_msg, data, pipe_msg->size)
-			> sizeof(struct mousevsc_prt_msg)) {
-			WARN_ON(1);
+		if (WARN_ON(len > sizeof(struct mousevsc_prt_msg)))
 			break;
-		}
 
-		memcpy(&input_dev->protocol_resp, pipe_msg,
-				struct_size(pipe_msg, data, pipe_msg->size));
+		memcpy(&input_dev->protocol_resp, pipe_msg, len);
 		complete(&input_dev->wait_event);
 		break;