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    Subject[PATCH 5.5 127/170] xfrm: fix uctx len check in verify_sec_ctx_len
    Date
    From: Xin Long <lucien.xin@gmail.com>

    commit 171d449a028573b2f0acdc7f31ecbb045391b320 upstream.

    It's not sufficient to do 'uctx->len != (sizeof(struct xfrm_user_sec_ctx) +
    uctx->ctx_len)' check only, as uctx->len may be greater than nla_len(rt),
    in which case it will cause slab-out-of-bounds when accessing uctx->ctx_str
    later.

    This patch is to fix it by return -EINVAL when uctx->len > nla_len(rt).

    Fixes: df71837d5024 ("[LSM-IPSec]: Security association restriction.")
    Signed-off-by: Xin Long <lucien.xin@gmail.com>
    Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    net/xfrm/xfrm_user.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/net/xfrm/xfrm_user.c
    +++ b/net/xfrm/xfrm_user.c
    @@ -110,7 +110,8 @@ static inline int verify_sec_ctx_len(str
    return 0;

    uctx = nla_data(rt);
    - if (uctx->len != (sizeof(struct xfrm_user_sec_ctx) + uctx->ctx_len))
    + if (uctx->len > nla_len(rt) ||
    + uctx->len != (sizeof(struct xfrm_user_sec_ctx) + uctx->ctx_len))
    return -EINVAL;

    return 0;

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