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    Subject[PATCH AUTOSEL 4.19 41/68] Revert "HID: uhid: use strlcpy() instead of strncpy()"
    Date
    From: David Herrmann <dh.herrmann@gmail.com>

    [ Upstream commit 4d26d1d1e8065bb3326a7c06d5d4698e581443a9 ]

    This reverts commit 336fd4f5f25157e9e8bd50e898a1bbcd99eaea46.

    Please note that `strlcpy()` does *NOT* do what you think it does.
    strlcpy() *ALWAYS* reads the full input string, regardless of the
    'length' parameter. That is, if the input is not zero-terminated,
    strlcpy() will *READ* beyond input boundaries. It does this, because it
    always returns the size it *would* copy if the target was big enough,
    not the truncated size it actually copied.

    The original code was perfectly fine. The hid device is
    zero-initialized and the strncpy() functions copied up to n-1
    characters. The result is always zero-terminated this way.

    This is the third time someone tried to replace strncpy with strlcpy in
    this function, and gets it wrong. I now added a comment that should at
    least make people reconsider.

    Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
    Signed-off-by: Jiri Kosina <jkosina@suse.cz>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/hid/uhid.c | 13 +++++++------
    1 file changed, 7 insertions(+), 6 deletions(-)

    diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
    index 051639c09f72..840634e0f1e3 100644
    --- a/drivers/hid/uhid.c
    +++ b/drivers/hid/uhid.c
    @@ -497,12 +497,13 @@ static int uhid_dev_create2(struct uhid_device *uhid,
    goto err_free;
    }

    - len = min(sizeof(hid->name), sizeof(ev->u.create2.name));
    - strlcpy(hid->name, ev->u.create2.name, len);
    - len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys));
    - strlcpy(hid->phys, ev->u.create2.phys, len);
    - len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq));
    - strlcpy(hid->uniq, ev->u.create2.uniq, len);
    + /* @hid is zero-initialized, strncpy() is correct, strlcpy() not */
    + len = min(sizeof(hid->name), sizeof(ev->u.create2.name)) - 1;
    + strncpy(hid->name, ev->u.create2.name, len);
    + len = min(sizeof(hid->phys), sizeof(ev->u.create2.phys)) - 1;
    + strncpy(hid->phys, ev->u.create2.phys, len);
    + len = min(sizeof(hid->uniq), sizeof(ev->u.create2.uniq)) - 1;
    + strncpy(hid->uniq, ev->u.create2.uniq, len);

    hid->ll_driver = &uhid_hid_driver;
    hid->bus = ev->u.create2.bus;
    --
    2.17.1
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