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-rw-r--r--include/uapi/linux/shm.h17
1 files changed, 9 insertions, 8 deletions
diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h
index 78b69413f582..1fbf24ea37fd 100644
--- a/include/uapi/linux/shm.h
+++ b/include/uapi/linux/shm.h
@@ -8,19 +8,20 @@
#endif
/*
- * SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
- * be increased by sysctl
+ * SHMMNI, SHMMAX and SHMALL are default upper limits which can be
+ * modified by sysctl. The SHMMAX and SHMALL values have been chosen to
+ * be as large possible without facilitating scenarios where userspace
+ * causes overflows when adjusting the limits via operations of the form
+ * "retrieve current limit; add X; update limit". It is therefore not
+ * advised to make SHMMAX and SHMALL any larger. These limits are
+ * suitable for both 32 and 64-bit systems.
*/
-
-#define SHMMAX 0x2000000 /* max shared seg size (bytes) */
#define SHMMIN 1 /* min shared seg size (bytes) */
#define SHMMNI 4096 /* max num of segs system wide */
-#ifndef __KERNEL__
-#define SHMALL (SHMMAX/getpagesize()*(SHMMNI/16))
-#endif
+#define SHMMAX (ULONG_MAX - (1UL << 24)) /* max shared seg size (bytes) */
+#define SHMALL (ULONG_MAX - (1UL << 24)) /* max shm system wide (pages) */
#define SHMSEG SHMMNI /* max shared segs per process */
-
/* Obsolete, used only for backwards compatibility and libc5 compiles */
struct shmid_ds {
struct ipc_perm shm_perm; /* operation perms */