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    Subject[PATCH 5.19 0950/1157] lib/bitmap: fix off-by-one in bitmap_to_arr64()
    Date
    From: Alexander Lobakin <alexandr.lobakin@intel.com>

    [ Upstream commit 428bc098635680a664779f26f24fe9197d186172 ]

    GENMASK*() family takes the first and the last bits of the mask
    *including* them. So, with the current code bitmap_to_arr64()
    doesn't clear the tail properly:

    nbits % exp mask must be
    1 GENMASK(1, 0) 0x3 0x1
    ...
    63 GENMASK(63, 0) 0xffffffffffffffff 0x7fffffffffffffff

    This was found by making the function always available instead of
    32-bit BE systems only (for reusing in some new functionality).
    Turn the number of bits into the last bit set by subtracting 1.
    @nbits is already checked to be positive beforehand.

    Fixes: 0a97953fd221 ("lib: add bitmap_{from,to}_arr64")
    Signed-off-by: Alexander Lobakin <alexandr.lobakin@intel.com>
    Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
    Signed-off-by: Yury Norov <yury.norov@gmail.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    lib/bitmap.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/lib/bitmap.c b/lib/bitmap.c
    index b18e31ea6e66..e903e13c62e1 100644
    --- a/lib/bitmap.c
    +++ b/lib/bitmap.c
    @@ -1564,7 +1564,7 @@ void bitmap_to_arr64(u64 *buf, const unsigned long *bitmap, unsigned int nbits)

    /* Clear tail bits in the last element of array beyond nbits. */
    if (nbits % 64)
    - buf[-1] &= GENMASK_ULL(nbits % 64, 0);
    + buf[-1] &= GENMASK_ULL((nbits - 1) % 64, 0);
    }
    EXPORT_SYMBOL(bitmap_to_arr64);
    #endif
    --
    2.35.1


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