Shared memory segment can be abused to trigger out-of-memory conditions and
the standard measures against out-of-memory do not work:
- It is not possible to use setrlimit to limit the size of shm segments.
- Segments can exist without association with any processes, thus
the oom-killer is unable to free that memory.
Therefore Linux always limited the size of segments by default to 32 MB.
As most systems do not need a protection against malicious user space apps,
a default that forces most admins and distros to change it doesn't make
sense.
The patch disables both limits by setting the limits to ULONG_MAX.
Admins who need a protection against out-of-memory conditions should
reduce the limits again and/or enable shm_rmid_forced.
Davidlohr: What do you think?
I prefer this approach: No need to update the man pages, smaller change
of the code, smaller risk of user space incompatibilities.
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
---
include/linux/shm.h | 2 +-
include/uapi/linux/shm.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/linux/shm.h b/include/linux/shm.h
index 1e2cd2e..37bf9c6 100644
--- a/include/linux/shm.h
+++ b/include/linux/shm.h
@@ -4,7 +4,7 @@
#include <asm/page.h>
#include <uapi/linux/shm.h>
-#define SHMALL (SHMMAX/PAGE_SIZE*(SHMMNI/16)) /* max shm system wide (pages) */
+#define SHMALL ULONG_MAX /* max shm system wide (pages) */
#include <asm/shmparam.h>
struct shmid_kernel /* private to the kernel */
{
diff --git a/include/uapi/linux/shm.h b/include/uapi/linux/shm.h
index 78b6941..d9497b7 100644
--- a/include/uapi/linux/shm.h
+++ b/include/uapi/linux/shm.h
@@ -12,7 +12,7 @@
* be increased by sysctl
*/
-#define SHMMAX 0x2000000 /* max shared seg size (bytes) */
+#define SHMMAX ULONG_MAX /* max shared seg size (bytes) */
#define SHMMIN 1 /* min shared seg size (bytes) */
#define SHMMNI 4096 /* max num of segs system wide */
#ifndef __KERNEL__
--
1.9.0
--
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