On 10/11/2021 2:33 PM, Paul Moore wrote:
On Wed, Oct 6, 2021 at 8:46 PM Todd Kjos tkjos@google.com wrote:
Use the 'struct cred' saved at binder_open() to lookup the security ID via security_cred_getsecid(). This ensures that the security context that opened binder is the one used to generate the secctx.
Fixes: ec74136ded79 ("binder: create node flag to request sender's security context") Signed-off-by: Todd Kjos tkjos@google.com Suggested-by: Stephen Smalley stephen.smalley.work@gmail.com Reported-by: kernel test robot lkp@intel.com Cc: stable@vger.kernel.org # 5.4+
v3: added this patch to series v4: fix build-break for !CONFIG_SECURITY
drivers/android/binder.c | 11 +---------- include/linux/security.h | 4 ++++ 2 files changed, 5 insertions(+), 10 deletions(-)
diff --git a/drivers/android/binder.c b/drivers/android/binder.c index ca599ebdea4a..989afd0804ca 100644 --- a/drivers/android/binder.c +++ b/drivers/android/binder.c @@ -2722,16 +2722,7 @@ static void binder_transaction(struct binder_proc *proc, u32 secid; size_t added_size;
/** Arguably this should be the task's subjective LSM secid but* we can't reliably access the subjective creds of a task* other than our own so we must use the objective creds, which* are safe to access. The downside is that if a task is* temporarily overriding it's creds it will not be reflected* here; however, it isn't clear that binder would handle that* case well anyway.*/security_task_getsecid_obj(proc->tsk, &secid);
security_cred_getsecid(proc->cred, &secid); ret = security_secid_to_secctx(secid, &secctx, &secctx_sz); if (ret) { return_error = BR_FAILED_REPLY;diff --git a/include/linux/security.h b/include/linux/security.h index 6344d3362df7..f02cc0211b10 100644 --- a/include/linux/security.h +++ b/include/linux/security.h @@ -1041,6 +1041,10 @@ static inline void security_transfer_creds(struct cred *new, { }
+static inline void security_cred_getsecid(const struct cred *c, u32 *secid) +{ +}
Since security_cred_getsecid() doesn't return an error code we should probably set the secid to 0 in this case, for example:
static inline void security_cred_getsecid(...) { *secid = 0; }
If CONFIG_SECURITY is unset there shouldn't be any case where the secid value is ever used for anything. Are you suggesting that it be set out of an abundance of caution?