linux-kernel - Re: [regression v2.6.38] Re: [PATCH v2] brk: fix min_brk lower bound computation for COMPAT

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Date:	Tue, 29 Mar 2011 22:24:21 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Jiri Kosina <jkosina@...e.cz>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	"Linux/m68k" <linux-m68k@...r.kernel.org>
Subject: Re: [regression v2.6.38] Re: [PATCH v2] brk: fix min_brk lower bound
 computation for COMPAT_BRK

Hi Jiri,

On Mon, Mar 28, 2011 at 16:20, Jiri Kosina <jkosina@...e.cz> wrote:
> On Sat, 26 Mar 2011, Geert Uytterhoeven wrote:
>> >> | RAMDISK: gzip image found at block 0
>> >> | VFS: Mounted root (ext2 filesystem) readonly on device 1:0.
>> >> | warning: process `update' used the obsolete bdflush system call
>> >> | Fix your initscripts?
>> >> | init: cannot open inittab
>> >> | Kernel panic - not syncing: Attempted to kill init!

> Hmm, I think we'd need some refresh on what the ancient libc5-based
> binaries are actually doing.
>
> Could you please send me strace of this application (restricting it to
> brk()/mmap() calls should be enough).

I managed to reproduce it inside ARAnyM, by chrooting into the ramdisk image.
After adding strace, "strace /sbin/init" for the success case gives:

old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xc0004000
old_mmap(NULL, 578, PROT_READ, MAP_SHARED, 3, 0) = 0xc0007000
old_mmap(NULL, 663552, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xc0008000
old_mmap(0xc0008000, 426908, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED, 3, 0) = 0xc0008000
old_mmap(0xc0072000, 24256, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED, 3, 0x68000) = 0xc0072000
old_mmap(0xc0078000, 204696, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xc0078000
brk(0x80005c8e)                         = 0x80005c8e
brk(0x80006000)                         = 0x80006000
old_mmap(NULL, 1024, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xc0007000

For the failure case:

old_mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xc0004000
old_mmap(NULL, 578, PROT_READ, MAP_SHARED, 3, 0) = 0xc0007000
old_mmap(NULL, 663552, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xc0008000
old_mmap(0xc0008000, 426908, PROT_READ|PROT_EXEC,
MAP_PRIVATE|MAP_FIXED, 3, 0) = 0xc0008000
old_mmap(0xc0072000, 24256, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED, 3, 0x68000) = 0xc0072000
old_mmap(0xc0078000, 204696, PROT_READ|PROT_WRITE,
MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0xc0078000
brk(0x80005c8e)                         = 0x80006000

Major difference:

-brk(0x80005c8e)                         = 0x80005c8e
-brk(0x80006000)                         = 0x80006000
-open("/etc/inittab", O_RDONLY)          = 3
-fstat(3, {st_mode=S_IFREG|0644, st_size=140, ...}) = 0
-old_mmap(NULL, 1024, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS,
-1, 0) = 0xc0007000
-read(3, "tty1:console:/sbin/getty 9600 tt"..., 1024) = 140
-read(3, "", 1024)                       = 0
+brk(0x80005c8e)                         = 0x80006000
+open("/dev/console", O_WRONLY)          = 3
+write(3, "init: ", 6)                   = 6
+write(3, "cannot open inittab\n", 20)   = 20
 close(3)                                = 0

Seems like the binary doesn't like brk() rounding up the requested
value to the next page...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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