"ps -e" without procfs(5)

[Kostik Belousov]

On Tue, Nov 01, 2011 at 09:07:11AM +0200, Mikolaj Golub wrote:
> 
> On Mon, 31 Oct 2011 11:49:48 +0200 Kostik Belousov wrote:
> 
>  KB> For PROC_ARG and PROC_ENV, you blindly trust the read values of the arg and
>  KB> env vector sizes. This can easily cause kernel panics due to unability to
>  KB> malloc the requested memory. I recommend to put some clump, and twice
>  KB> of (PATH_MAX + ARG_MAX) is probably enough (see kern_exec.c, in particular,
>  KB> exec_alloc_args). Also, you might use the swappable memory for the strings
>  KB> as well, in the style of exec_alloc_args().
> 
> After looking at it more closely, I am not sure if I need to use
> exec_alloc_args. I malloc explicitly only for array vector (proc_vector). And
> actually it should be much smaller than 2 * (PATH_MAX + ARG_MAX). Currently in
> linprocfs the limit is 512 entries:
> 
>         #define MAX_ARGV_STR    512     /* Max number of argv-like strings */
> 
> The same limit is in libkvm:
> 
>         /*
>          * Check that there aren't an unreasonable number of arguments,
>          * and that the address is in user space.  Special test for
>          * VM_MIN_ADDRESS as it evaluates to zero, but is not a simple zero
>          * constant for some archs.  We cannot use the pre-processor here and
>          * for some archs the compiler would trigger a signedness warning.
>          */
>         if (narg > 512 || addr + 1 < VM_MIN_ADDRESS + 1 || addr >= VM_MAXUSER_ADDRESS)
>                 return (0);
> 
> (BTW, may be the VM_MIN_ADDRESS - VM_MAXUSER_ADDRESS is worth adding in my
> code too?)
> 
> So it looks like I should use the same limit (512 * sizeof(char *)) for the
> allocated array. I could use exec_alloc_args() for the allocation but it would
> reqire some changes: I would have to free using kmem_free_wakeup(), which
> requires size of the region, while I return the number of entries. So I'd
> rather not use exec_alloc_args() for vector allocation because the benefit is
> not significant here.
> 
> For strings I use sbuf and set it up using sbuf_new_for_sysctl. I could set it
> up manually as SBUF_FIXEDLEN allocating buf (up to 2 * (PATH_MAX + ARG_MAX))
> with exec_alloc_args() but this would complicate things a little. Do you think
> it is worth doing?
I mean using the swappable memory for strings, i.e. for the data you are
currently store in sbuf. It indeed may be tricky, it was only an idea.
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