Re: [patch 1/5] jffs2: fix memory corruption in jffs2_read_inode_range()

[Artem Bityutskiy <dedekind1@gmail.com>]

On Tue, 2010-02-02 at 14:43 -0800, akpm@linux-foundation.org wrote:
> From: Anton Vorontsov <avorontsov@ru.mvista.com>
> 
> In 2.6.23 kernel, commit a32ea1e1f925399e0d81ca3f7394a44a6dafa12c ("Fix
> read/truncate race") fixed a race in the generic code, and as a side
> effect, now do_generic_file_read() can ask us to readpage() past the
> i_size, which seems to be correctly handled by the block routines (e.g. 
> block_read_full_page() fills the page with zeroes in case if somebody is
> trying to read past the last inode's block).
> 
> JFFS2 doesn't handle this, instead jffs2_read_inode_range() is trying to
> lookup the fragments which do not belong to anything, and
> jffs2_lookup_node_frag() happily returns "the closest smaller match" which
> is OK for most cases (I guess), but in our case there wasn't anything
> meaningful to lookup in the first place.
> 
> After we found the bogus fragment, the code can branch to 'Filling frag
> hole' case that does
> 
>   memset(buf, 0, min(end, frag->ofs + frag->size) - offset);
> 
> and since 'frag' is bogus, its ofs + size can be smaller than the real
> 'offset' (i.e.  index << PAGE_CACHE_SHIFT), and so the code turns into
> 
>   memset(buf, 0, <huge unsigned negative>);
> 
> Hopefully, in most cases the corruption is fatal, and quickly causing
> random oopses, like this:
> 
>   root@10.0.0.4:~/ltp-fs-20090531# ./testcases/kernel/fs/ftest/ftest01
>   Unable to handle kernel paging request for data at address 0x00000008
>   Faulting instruction address: 0xc01cd980
>   Oops: Kernel access of bad area, sig: 11 [#1]
>   [...]
>   NIP [c01cd980] rb_insert_color+0x38/0x184
>   LR [c0043978] enqueue_hrtimer+0x88/0xc4
>   Call Trace:
>   [c6c63b60] [c004f9a8] tick_sched_timer+0xa0/0xe4 (unreliable)
>   [c6c63b80] [c0043978] enqueue_hrtimer+0x88/0xc4
>   [c6c63b90] [c0043a48] __run_hrtimer+0x94/0xbc
>   [c6c63bb0] [c0044628] hrtimer_interrupt+0x140/0x2b8
>   [c6c63c10] [c000f8e8] timer_interrupt+0x13c/0x254
>   [c6c63c30] [c001352c] ret_from_except+0x0/0x14
>   --- Exception: 901 at memset+0x38/0x5c
>       LR = jffs2_read_inode_range+0x144/0x17c
>   [c6c63cf0] [00000000] (null) (unreliable)
> 
> This patch fixes the issue, plus fixes all LTP tests on NAND/UBI with
> JFFS2 filesystem that were failing since 2.6.23 (seems like the bug above
> also broke the truncation).
> 
> Note that the bug is only reproducible with write-buffered MTD devices
> (e.g.  NAND, UBI), which is a mystery to me (though I didn't look close
> enough, possibly there is a race between gc and wbuf code, but I don't see
> it and obviously it isn't that fatal).
> 
> Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
> Cc: David Woodhouse <dwmw2@infradead.org>
> Cc: Neil Brown <neilb@suse.de>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

All 5 patches you sent in this series are also sitting in my l2-mtd-2.6
tree.

-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)