> This patch adds the documentation for the following parameters:
Sysctl seems really strange to me. Either the feature is safe to use,
or it is not. Users can already ulimit -c 0, and we do not have
Plus, this is pretty analogical to ulimit -c, so I believe it should
be implemented like that one. You'll need less locking that way.
> +2.14 /proc/<pid>/core_flags - Core dump control flags
> +When a process is dumped, all anonymous memory is written to a core file as
> +long as the size of the core file isn't limited. But sometimes we don't want
> +to dump some memory segments, for example, huge shared memory.
> +The /proc/<pid>/core_flags file enables you to omit some anonymous memory from
> +a core file when it is generated. The content of the proc file is bitmask of
> +memory segment types you don't want to dump. When the <pid> process is dumped,
> +the core dump routine decides whether a given memory segment should be dumped
> +into a core file or not, based on the type of the memory segment and bitmask.
> +Currently, only valid bit is bit 0. If bit 0 is set, anonymous `shared' memory
> +segments are not dumped. There are three types of anonymous shared memory:
> + - IPC shared memory
> + - the memory segments created by mmap(2) with MAP_ANONYMOUS and MAP_SHARED
> + flags
> + - the memory segments created by mmap(2) with MAP_SHARED flag, and the
> + mapped file has already been unlinked
> +Because current core dump routine doesn't distinguish these segments, you can
> +only choose either dumping all anonymous shared memory segments or not.
> +If you don't want to dump all shared memory segments attached to pid 1234, set
> +the bit 0 of the process's core_flags to 1:
> + $ echo 1 > /proc/1234/core_flags
> +Additionally, you can check its hexadecimal value by reading the file:
> + $ cat /proc/1234/core_flags
> + 00000001
> +When a new process is created, the process inherits the core_flags setting
> +from its parent. It is useful to set the core_flags before the program runs.
> +For example:
> + $ echo 1 > /proc/self/core_flags
> + $ ./some_program
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Pavel Machek wrote:
>>This patch adds the documentation for the following parameters:
> Sysctl seems really strange to me. Either the feature is safe to use,
> or it is not. Users can already ulimit -c 0, and we do not have
Oh, I had forgotten that. Thank you for pointing out. The purpose of
this sysctl is to prevent a bad process from hiding its memory.
But as you say, this sysctl isn't enough for the purpose.
> Does this feature have any security implications? For example, there might
> be system administration programs which force a coredump on a "bad"
> process, and leave the core somewhere for the administrator to look at.
I have never heard of the story that ulimit -c 0 bothered an
administrator who wanted to force a coredump. So even without this
sysctl, the administrator wouldn't bother about security concerns.
I'll drop it from the next version.
Hitachi, Ltd., Systems Development Laboratory