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KEYS: fix dereferencing NULL payload with nonzero length

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.

Cc: stable@vger.kernel.org # 2.6.10+
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>
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ebiggers authored and James Morris committed Jun 8, 2017
1 parent 0f534e4 commit 5649645d725c73df4302428ee4e02c869248b4c5
Showing with 2 additions and 2 deletions.
  1. +2 −2 security/keys/keyctl.c
@@ -99,7 +99,7 @@ SYSCALL_DEFINE5(add_key, const char __user *, _type,
/* pull the payload in if one was supplied */
payload = NULL;

if (_payload) {
if (plen) {
ret = -ENOMEM;
payload = kvmalloc(plen, GFP_KERNEL);
if (!payload)
@@ -324,7 +324,7 @@ 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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