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    Subject[PATCH 5.10 35/38] mac80211: fix potential double free on mesh join
    Date
    From: Linus Lüssing <ll@simonwunderlich.de>

    commit 4a2d4496e15ea5bb5c8e83b94ca8ca7fb045e7d3 upstream.

    While commit 6a01afcf8468 ("mac80211: mesh: Free ie data when leaving
    mesh") fixed a memory leak on mesh leave / teardown it introduced a
    potential memory corruption caused by a double free when rejoining the
    mesh:

    ieee80211_leave_mesh()
    -> kfree(sdata->u.mesh.ie);
    ...
    ieee80211_join_mesh()
    -> copy_mesh_setup()
    -> old_ie = ifmsh->ie;
    -> kfree(old_ie);

    This double free / kernel panics can be reproduced by using wpa_supplicant
    with an encrypted mesh (if set up without encryption via "iw" then
    ifmsh->ie is always NULL, which avoids this issue). And then calling:

    $ iw dev mesh0 mesh leave
    $ iw dev mesh0 mesh join my-mesh

    Note that typically these commands are not used / working when using
    wpa_supplicant. And it seems that wpa_supplicant or wpa_cli are going
    through a NETDEV_DOWN/NETDEV_UP cycle between a mesh leave and mesh join
    where the NETDEV_UP resets the mesh.ie to NULL via a memcpy of
    default_mesh_setup in cfg80211_netdev_notifier_call, which then avoids
    the memory corruption, too.

    The issue was first observed in an application which was not using
    wpa_supplicant but "Senf" instead, which implements its own calls to
    nl80211.

    Fixing the issue by removing the kfree()'ing of the mesh IE in the mesh
    join function and leaving it solely up to the mesh leave to free the
    mesh IE.

    Cc: stable@vger.kernel.org
    Fixes: 6a01afcf8468 ("mac80211: mesh: Free ie data when leaving mesh")
    Reported-by: Matthias Kretschmer <mathias.kretschmer@fit.fraunhofer.de>
    Signed-off-by: Linus Lüssing <ll@simonwunderlich.de>
    Tested-by: Mathias Kretschmer <mathias.kretschmer@fit.fraunhofer.de>
    Link: https://lore.kernel.org/r/20220310183513.28589-1-linus.luessing@c0d3.blue
    Signed-off-by: Johannes Berg <johannes.berg@intel.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    net/mac80211/cfg.c | 3 ---
    1 file changed, 3 deletions(-)

    --- a/net/mac80211/cfg.c
    +++ b/net/mac80211/cfg.c
    @@ -2076,14 +2076,12 @@ static int copy_mesh_setup(struct ieee80
    const struct mesh_setup *setup)
    {
    u8 *new_ie;
    - const u8 *old_ie;
    struct ieee80211_sub_if_data *sdata = container_of(ifmsh,
    struct ieee80211_sub_if_data, u.mesh);
    int i;

    /* allocate information elements */
    new_ie = NULL;
    - old_ie = ifmsh->ie;

    if (setup->ie_len) {
    new_ie = kmemdup(setup->ie, setup->ie_len,
    @@ -2093,7 +2091,6 @@ static int copy_mesh_setup(struct ieee80
    }
    ifmsh->ie_len = setup->ie_len;
    ifmsh->ie = new_ie;
    - kfree(old_ie);

    /* now copy the rest of the setup parameters */
    ifmsh->mesh_id_len = setup->mesh_id_len;

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