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    Subject[PATCH 5.10 136/452] bpf: Fix excessive memory allocation in stack_map_alloc()
    Date
    From: Yuntao Wang <ytcoode@gmail.com>

    [ Upstream commit b45043192b3e481304062938a6561da2ceea46a6 ]

    The 'n_buckets * (value_size + sizeof(struct stack_map_bucket))' part of the
    allocated memory for 'smap' is never used after the memlock accounting was
    removed, thus get rid of it.

    [ Note, Daniel:

    Commit b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
    moved `cost += n_buckets * (value_size + sizeof(struct stack_map_bucket))`
    up and therefore before the bpf_map_area_alloc() allocation, sigh. In a later
    step commit c85d69135a91 ("bpf: move memory size checks to bpf_map_charge_init()"),
    and the overflow checks of `cost >= U32_MAX - PAGE_SIZE` moved into
    bpf_map_charge_init(). And then 370868107bf6 ("bpf: Eliminate rlimit-based
    memory accounting for stackmap maps") finally removed the bpf_map_charge_init().
    Anyway, the original code did the allocation same way as /after/ this fix. ]

    Fixes: b936ca643ade ("bpf: rework memlock-based memory accounting for maps")
    Signed-off-by: Yuntao Wang <ytcoode@gmail.com>
    Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
    Link: https://lore.kernel.org/bpf/20220407130423.798386-1-ytcoode@gmail.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    kernel/bpf/stackmap.c | 1 -
    1 file changed, 1 deletion(-)

    diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
    index 4575d2d60cb1..c19e669afba0 100644
    --- a/kernel/bpf/stackmap.c
    +++ b/kernel/bpf/stackmap.c
    @@ -121,7 +121,6 @@ static struct bpf_map *stack_map_alloc(union bpf_attr *attr)
    return ERR_PTR(-E2BIG);

    cost = n_buckets * sizeof(struct stack_map_bucket *) + sizeof(*smap);
    - cost += n_buckets * (value_size + sizeof(struct stack_map_bucket));
    err = bpf_map_charge_init(&mem, cost);
    if (err)
    return ERR_PTR(err);
    --
    2.35.1


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