Re: Rationale for RLIMIT_MEMLOCK?

["Michael Kerrisk" <mtk-manpages@gmx.net>]

> > Matthias Andree <matthias.andree@gmx.de> wrote:

[...]

> The complete story is, condensed, and with return values, for a
> setuid-root application:
> 
>   geteuid() == 0;
>   mlockall(MLC_CURRENT|MLC_FUTURE) == (success);
>   seteuid(500) == (success);
>   valloc(64512 + pagesize) == NULL (failure);

[...]

A late follow-up to this thread. I've added the following text
to the mlockall() manual pag under BUGS:

    Since kernel 2.6.9, if a privileged process calls 
    mlockall(MCL_FUTURE) and later drops privileges
    (CAP_IPC_LOCK), then subsequent memory allocations
    (e.g., mmap(2), sbrk(2)) will fail if the 
    RLIMIT_MEMLOCK resource limit is encountered.
    
The change will be in man-pages 2.23.

Cheers,

Michael

-- 
Michael Kerrisk
maintainer of Linux man pages Sections 2, 3, 4, 5, and 7 

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