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    Subject[PATCH 5.10 274/663] HID: core: detect and skip invalid inputs to snto32()
    Date
    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 8a8b2b982f83c..097cb1ee31268 100644
    --- a/drivers/hid/hid-core.c
    +++ b/drivers/hid/hid-core.c
    @@ -1307,6 +1307,9 @@ 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


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