ipc: make shm_get_stat() more robust

shm_get_stat() assumes idr_find(&shm_ids(ns).ipcs_idr) returns "struct
shmid_kernel *"; all other callers assume that it returns "struct
kern_ipc_perm *".  This works because "struct kern_ipc_perm" is currently
the first member of "struct shmid_kernel", but it would be better to use
container_of() to prevent future breakage.

Signed-off-by: Tony Battersby <tonyb@cybernetics.com>
Cc: Jiri Olsa <olsajiri@gmail.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 2 deletions

diff --git a/ipc/shm.c b/ipc/shm.c
index f239d87e0d37..faa46da99ebe 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -555,12 +555,14 @@ static void shm_get_stat(struct ipc_namespace *ns, unsigned long *rss,
         in_use = shm_ids(ns).in_use;
 
         for (total = 0, next_id = 0; total < in_use; next_id++) {
+                struct kern_ipc_perm *ipc;
                 struct shmid_kernel *shp;
                 struct inode *inode;
 
-                shp = idr_find(&shm_ids(ns).ipcs_idr, next_id);
-                if (shp == NULL)
+                ipc = idr_find(&shm_ids(ns).ipcs_idr, next_id);
+                if (ipc == NULL)
                         continue;
+                shp = container_of(ipc, struct shmid_kernel, shm_perm);
 
                 inode = shp->shm_file->f_path.dentry->d_inode;