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    SubjectRe: [PATCH] fs, cifs: convert tcon_link.tl_count from atomic_t to refcount_t
    merged into cifs-2.6.git for-next

    On Mon, Oct 30, 2017 at 10:03 AM, Aurélien Aptel <aaptel@suse.com> wrote:
    > Elena Reshetova <elena.reshetova@intel.com> writes:
    >> atomic_t variables are currently used to implement reference
    >> counters with the following properties:
    >> - counter is initialized to 1 using atomic_set()
    >> - a resource is freed upon counter reaching zero
    >> - once counter reaches zero, its further
    >> increments aren't allowed
    >> - counter schema uses basic atomic operations
    >> (set, inc, inc_not_zero, dec_and_test, etc.)
    >>
    >> Such atomic variables should be converted to a newly provided
    >> refcount_t type and API that prevents accidental counter overflows
    >> and underflows. This is important since overflows and underflows
    >> can lead to use-after-free situation and be exploitable.
    >>
    >> The variable tcon_link.tl_count is used as pure reference counter.
    >> Convert it to refcount_t and fix up the operations.
    >
    > <snip>
    >
    >> - cifs_get_tlink(tlink);
    >> + refcount_set(&tlink->tl_count, 1);
    >
    > Since cifs_get_tlink() basically only increments the reference count and
    > given that this is a new tlink I also think this replacement is ok.
    >
    > Looks good to me and passes 'make C=1'.
    >
    > Reviewed-by: Aurelien Aptel <aaptel@suse.com>
    >
    > --
    > Aurélien Aptel / SUSE Labs Samba Team
    > GPG: 1839 CB5F 9F5B FB9B AA97 8C99 03C8 A49B 521B D5D3
    > SUSE Linux GmbH, Maxfeldstraße 5, 90409 Nürnberg, Germany
    > GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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    --
    Thanks,

    Steve

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