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    Subject[PATCH 3.8 31/81] net: fib: fib6_add: fix potential NULL pointer dereference
    Date
    3.8.13.12 -stable review patch.  If anyone has any objections, please let me know.

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

    From: Daniel Borkmann <dborkman@redhat.com>

    [ Upstream commit ae7b4e1f213aa659aedf9c6ecad0bf5f0476e1e2 ]

    When the kernel is compiled with CONFIG_IPV6_SUBTREES, and we return
    with an error in fn = fib6_add_1(), then error codes are encoded into
    the return pointer e.g. ERR_PTR(-ENOENT). In such an error case, we
    write the error code into err and jump to out, hence enter the if(err)
    condition. Now, if CONFIG_IPV6_SUBTREES is enabled, we check for:

    if (pn != fn && pn->leaf == rt)
    ...
    if (pn != fn && !pn->leaf && !(pn->fn_flags & RTN_RTINFO))
    ...

    Since pn is NULL and fn is f.e. ERR_PTR(-ENOENT), then pn != fn
    evaluates to true and causes a NULL-pointer dereference on further
    checks on pn. Fix it, by setting both NULL in error case, so that
    pn != fn already evaluates to false and no further dereference
    takes place.

    This was first correctly implemented in 4a287eba2 ("IPv6 routing,
    NLM_F_* flag support: REPLACE and EXCL flags support, warn about
    missing CREATE flag"), but the bug got later on introduced by
    188c517a0 ("ipv6: return errno pointers consistently for fib6_add_1()").

    Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
    Cc: Lin Ming <mlin@ss.pku.edu.cn>
    Cc: Matti Vaittinen <matti.vaittinen@nsn.com>
    Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>
    Acked-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
    Acked-by: Matti Vaittinen <matti.vaittinen@nsn.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Kamal Mostafa <kamal@canonical.com>
    ---
    net/ipv6/ip6_fib.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
    index 7c39aa6..b3adb7f 100644
    --- a/net/ipv6/ip6_fib.c
    +++ b/net/ipv6/ip6_fib.c
    @@ -827,9 +827,9 @@ int fib6_add(struct fib6_node *root, struct rt6_info *rt, struct nl_info *info)
    fn = fib6_add_1(root, &rt->rt6i_dst.addr, sizeof(struct in6_addr),
    rt->rt6i_dst.plen, offsetof(struct rt6_info, rt6i_dst),
    allow_create, replace_required);
    -
    if (IS_ERR(fn)) {
    err = PTR_ERR(fn);
    + fn = NULL;
    goto out;
    }

    --
    1.8.1.2


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