Messages in this thread Patch in this message | | | From | Manfred Spraul <> | Subject | [PATCH] ipc/shm: disable SHMALL, SHMMAX | Date | Sat, 12 Apr 2014 13:48:04 +0200 |
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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@colorfullife.com> --- 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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