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    Subject[PATCH 5.15 075/230] cxl/port: Hold port reference until decoder release
    Date
    From: Dan Williams <dan.j.williams@intel.com>

    [ Upstream commit 74be98774dfbc5b8b795db726bd772e735d2edd4 ]

    KASAN + DEBUG_KOBJECT_RELEASE reports a potential use-after-free in
    cxl_decoder_release() where it goes to reference its parent, a cxl_port,
    to free its id back to port->decoder_ida.

    BUG: KASAN: use-after-free in to_cxl_port+0x18/0x90 [cxl_core]
    Read of size 8 at addr ffff888119270908 by task kworker/35:2/379

    CPU: 35 PID: 379 Comm: kworker/35:2 Tainted: G OE 5.17.0-rc2+ #198
    Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015
    Workqueue: events kobject_delayed_cleanup
    Call Trace:
    <TASK>
    dump_stack_lvl+0x59/0x73
    print_address_description.constprop.0+0x1f/0x150
    ? to_cxl_port+0x18/0x90 [cxl_core]
    kasan_report.cold+0x83/0xdf
    ? to_cxl_port+0x18/0x90 [cxl_core]
    to_cxl_port+0x18/0x90 [cxl_core]
    cxl_decoder_release+0x2a/0x60 [cxl_core]
    device_release+0x5f/0x100
    kobject_cleanup+0x80/0x1c0

    The device core only guarantees parent lifetime until all children are
    unregistered. If a child needs a parent to complete its ->release()
    callback that child needs to hold a reference to extend the lifetime of
    the parent.

    Fixes: 40ba17afdfab ("cxl/acpi: Introduce cxl_decoder objects")
    Reported-by: Ben Widawsky <ben.widawsky@intel.com>
    Tested-by: Ben Widawsky <ben.widawsky@intel.com>
    Reviewed-by: Ben Widawsky <ben.widawsky@intel.com>
    Link: https://lore.kernel.org/r/164505751190.4175768.13324905271463416712.stgit@dwillia2-desk3.amr.corp.intel.com
    Signed-off-by: Dan Williams <dan.j.williams@intel.com>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/cxl/core/bus.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/drivers/cxl/core/bus.c b/drivers/cxl/core/bus.c
    index 267d8042bec2..0987a6423ee0 100644
    --- a/drivers/cxl/core/bus.c
    +++ b/drivers/cxl/core/bus.c
    @@ -182,6 +182,7 @@ static void cxl_decoder_release(struct device *dev)

    ida_free(&port->decoder_ida, cxld->id);
    kfree(cxld);
    + put_device(&port->dev);
    }

    static const struct device_type cxl_decoder_switch_type = {
    @@ -481,6 +482,9 @@ cxl_decoder_alloc(struct cxl_port *port, int nr_targets, resource_size_t base,
    if (rc < 0)
    goto err;

    + /* need parent to stick around to release the id */
    + get_device(&port->dev);
    +
    *cxld = (struct cxl_decoder) {
    .id = rc,
    .range = {
    --
    2.35.1


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