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    Subject[PATCH 4.20 58/65] intel_th: msu: Fix an off-by-one in attribute store
    Date
    4.20-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Alexander Shishkin <alexander.shishkin@linux.intel.com>

    commit ec5b5ad6e272d8d6b92d1007f79574919862a2d2 upstream.

    The 'nr_pages' attribute of the 'msc' subdevices parses a comma-separated
    list of window sizes, passed from userspace. However, there is a bug in
    the string parsing logic wherein it doesn't exclude the comma character
    from the range of characters as it consumes them. This leads to an
    out-of-bounds access given a sufficiently long list. For example:

    > # echo 8,8,8,8 > /sys/bus/intel_th/devices/0-msc0/nr_pages
    > ==================================================================
    > BUG: KASAN: slab-out-of-bounds in memchr+0x1e/0x40
    > Read of size 1 at addr ffff8803ffcebcd1 by task sh/825
    >
    > CPU: 3 PID: 825 Comm: npktest.sh Tainted: G W 4.20.0-rc1+
    > Call Trace:
    > dump_stack+0x7c/0xc0
    > print_address_description+0x6c/0x23c
    > ? memchr+0x1e/0x40
    > kasan_report.cold.5+0x241/0x308
    > memchr+0x1e/0x40
    > nr_pages_store+0x203/0xd00 [intel_th_msu]

    Fix this by accounting for the comma character.

    Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
    Fixes: ba82664c134ef ("intel_th: Add Memory Storage Unit driver")
    Cc: stable@vger.kernel.org # v4.4+
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/hwtracing/intel_th/msu.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/drivers/hwtracing/intel_th/msu.c
    +++ b/drivers/hwtracing/intel_th/msu.c
    @@ -1423,7 +1423,8 @@ nr_pages_store(struct device *dev, struc
    if (!end)
    break;

    - len -= end - p;
    + /* consume the number and the following comma, hence +1 */
    + len -= end - p + 1;
    p = end + 1;
    } while (len);


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