Hi Davidlohr,
On 04/18/2014 03:25 AM, Davidlohr Bueso wrote:
So a value of 0 bytes or pages, for shmmax and shmall, respectively,
implies unlimited memory, as opposed to disabling sysv shared memory.
That might be a second risk:
Right now, a sysadmin can prevent sysv memory allocations with
# sysctl kernel.shmall=0
After your patch is applied, this line allows unlimited allocations.
Obviously my patch has the opposite problem: 64-bit wrap-arounds.
--- a/include/uapi/linux/shm.h
+++ b/include/uapi/linux/shm.h
@@ -9,14 +9,14 @@
/*
* SHMMAX, SHMMNI and SHMALL are upper limits are defaults which can
- * be increased by sysctl
+ * be modified by sysctl. By default, disable SHMMAX and SHMALL with
+ * 0 bytes, thus allowing processes to have unlimited shared memory.
*/
-
-#define SHMMAX 0x2000000 /* max shared seg size (bytes) */
+#define SHMMAX 0 /* 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))
+#define SHMALL 0
#endif
#define SHMSEG SHMMNI /* max shared segs per process */
The "#ifndef __KERNEL__" is not required:
As there is no reference to PAGE_SIZE anymore, one definition for SHMALL
is sufficient.
--
Manfred
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