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    Subject[PATCH 3.16 175/233] KEYS: fix dereferencing NULL payload with nonzero length
    3.16.48-rc1 review patch.  If anyone has any objections, please let me know.

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

    From: Eric Biggers <ebiggers@google.com>

    commit 5649645d725c73df4302428ee4e02c869248b4c5 upstream.

    sys_add_key() and the KEYCTL_UPDATE operation of sys_keyctl() allowed a
    NULL payload with nonzero length to be passed to the key type's
    ->preparse(), ->instantiate(), and/or ->update() methods. Various key
    types including asymmetric, cifs.idmap, cifs.spnego, and pkcs7_test did
    not handle this case, allowing an unprivileged user to trivially cause a
    NULL pointer dereference (kernel oops) if one of these key types was
    present. Fix it by doing the copy_from_user() when 'plen' is nonzero
    rather than when '_payload' is non-NULL, causing the syscall to fail
    with EFAULT as expected when an invalid buffer is specified.

    Signed-off-by: Eric Biggers <ebiggers@google.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    Signed-off-by: James Morris <james.l.morris@oracle.com>
    [bwh: Backported to 3.16: adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    security/keys/keyctl.c | 4 ++--
    1 file changed, 2 insertions(+), 2 deletions(-)

    --- a/security/keys/keyctl.c
    +++ b/security/keys/keyctl.c
    @@ -97,7 +97,7 @@ SYSCALL_DEFINE5(add_key, const char __us
    payload = NULL;

    vm = false;
    - if (_payload) {
    + if (plen) {
    ret = -ENOMEM;
    payload = kmalloc(plen, GFP_KERNEL | __GFP_NOWARN);
    if (!payload) {
    @@ -331,7 +331,7 @@ long keyctl_update_key(key_serial_t id,

    /* pull the payload in if one was supplied */
    payload = NULL;
    - if (_payload) {
    + if (plen) {
    ret = -ENOMEM;
    payload = kmalloc(plen, GFP_KERNEL);
    if (!payload)
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