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    Subject[PATCH 4.19 117/271] rslib: Fix decoding of shortened codes
    Date
    [ Upstream commit 2034a42d1747fc1e1eeef2c6f1789c4d0762cb9c ]

    The decoding of shortenend codes is broken. It only works as expected if
    there are no erasures.

    When decoding with erasures, Lambda (the error and erasure locator
    polynomial) is initialized from the given erasure positions. The pad
    parameter is not accounted for by the initialisation code, and hence
    Lambda is initialized from incorrect erasure positions.

    The fix is to adjust the erasure positions by the supplied pad.

    Signed-off-by: Ferdinand Blomqvist <ferdinand.blomqvist@gmail.com>
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Link: https://lkml.kernel.org/r/20190620141039.9874-3-ferdinand.blomqvist@gmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    lib/reed_solomon/decode_rs.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    diff --git a/lib/reed_solomon/decode_rs.c b/lib/reed_solomon/decode_rs.c
    index 1db74eb098d0..3313bf944ff1 100644
    --- a/lib/reed_solomon/decode_rs.c
    +++ b/lib/reed_solomon/decode_rs.c
    @@ -99,9 +99,9 @@
    if (no_eras > 0) {
    /* Init lambda to be the erasure locator polynomial */
    lambda[1] = alpha_to[rs_modnn(rs,
    - prim * (nn - 1 - eras_pos[0]))];
    + prim * (nn - 1 - (eras_pos[0] + pad)))];
    for (i = 1; i < no_eras; i++) {
    - u = rs_modnn(rs, prim * (nn - 1 - eras_pos[i]));
    + u = rs_modnn(rs, prim * (nn - 1 - (eras_pos[i] + pad)));
    for (j = i + 1; j > 0; j--) {
    tmp = index_of[lambda[j - 1]];
    if (tmp != nn) {
    --
    2.20.1


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