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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        syzbot+1e911ad71dd4ea72e04a@syzkaller.appspotmail.com,
        Jiri Kosina <jikos@kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@redhat.com>,
        linux-input@vger.kernel.org, Jiri Kosina <jkosina@suse.cz>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 5.4 137/340] HID: core: detect and skip invalid inputs to snto32()
Date:   Mon,  1 Mar 2021 17:11:21 +0100
Message-Id: <20210301161055.058755105@linuxfoundation.org>
In-Reply-To: <20210301161048.294656001@linuxfoundation.org>
References: <20210301161048.294656001@linuxfoundation.org>
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From: Randy Dunlap <rdunlap@infradead.org>

[ Upstream commit a0312af1f94d13800e63a7d0a66e563582e39aec ]

Prevent invalid (0, 0) inputs to hid-core's snto32() function.

Maybe it is just the dummy device here that is causing this, but
there are hundreds of calls to snto32(0, 0). Having n (bits count)
of 0 is causing the current UBSAN trap with a shift value of
0xffffffff (-1, or n - 1 in this function).

Either of the value to shift being 0 or the bits count being 0 can be
handled by just returning 0 to the caller, avoiding the following
complex shift + OR operations:

	return value & (1 << (n - 1)) ? value | (~0U << n) : value;

Fixes: dde5845a529f ("[PATCH] Generic HID layer - code split")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: syzbot+1e911ad71dd4ea72e04a@syzkaller.appspotmail.com
Cc: Jiri Kosina <jikos@kernel.org>
Cc: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/hid/hid-core.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
index 263eca119ff0f..8d202011b2db5 100644
--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1300,6 +1300,9 @@ EXPORT_SYMBOL_GPL(hid_open_report);
 
 static s32 snto32(__u32 value, unsigned n)
 {
+	if (!value || !n)
+		return 0;
+
 	switch (n) {
 	case 8:  return ((__s8)value);
 	case 16: return ((__s16)value);
-- 
2.27.0