Re: [PATCH v3] ipc,shm: disable shmmax and shmall by default
From: Manfred Spraul <hidden>
Date: 2014-04-18 09:26:38
Also in:
linux-mm, lkml
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.
quoted hunk ↗ jump to hunk
--- 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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