ipc: add missing container_of()s for randstruct

When building with the randstruct gcc plugin, the layout of the IPC
structs will be randomized, which requires any sub-structure accesses to
use container_of().  The proc display handlers were missing the needed
container_of()s since the iterator is passing in the top-level struct
kern_ipc_perm.

This would lead to crashes when running the "lsipc" program after the
system had IPC registered (e.g. after starting up Gnome):

  general protection fault: 0000 [#1] PREEMPT SMP
  ...
  RIP: 0010:shm_add_rss_swap.isra.1+0x13/0xa0
  ...
  Call Trace:
    sysvipc_shm_proc_show+0x5e/0x150
    sysvipc_proc_show+0x1a/0x30
    seq_read+0x2e9/0x3f0
  ...

Link: http://lkml.kernel.org/r/20170730205950.GA55841@beast
Fixes: 3859a271a003 ("randstruct: Mark various structs for randomization")
Signed-off-by: Kees Cook <keescook@chromium.org>
Reported-by: Dominik Brodowski <linux@dominikbrodowski.net>
Acked-by: Davidlohr Bueso <dave@stgolabs.net>
Acked-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/ipc/sem.c b/ipc/sem.c
index 9e70cd7..38371e9 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2179,7 +2179,8 @@ void exit_sem(struct task_struct *tsk)
 static int sysvipc_sem_proc_show(struct seq_file *s, void *it)
 {
 	struct user_namespace *user_ns = seq_user_ns(s);
-	struct sem_array *sma = it;
+	struct kern_ipc_perm *ipcp = it;
+	struct sem_array *sma = container_of(ipcp, struct sem_array, sem_perm);
 	time_t sem_otime;
 
 	/*