[PATCH] jffs2: Fix memory corruption in jffs2_read_inode_range()

[Anton Vorontsov]

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 at 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 at ru.mvista.com>
---
 fs/jffs2/file.c |    8 +++++++-
 1 files changed, 7 insertions(+), 1 deletions(-)

diff --git a/fs/jffs2/file.c b/fs/jffs2/file.c
index 5edc2bf..e1d7a1d 100644
--- a/fs/jffs2/file.c
+++ b/fs/jffs2/file.c
@@ -85,7 +85,13 @@ static int jffs2_do_readpage_nolock (struct inode *inode, struct page *pg)
 	pg_buf = kmap(pg);
 	/* FIXME: Can kmap fail? */
 
-	ret = jffs2_read_inode_range(c, f, pg_buf, pg->index << PAGE_CACHE_SHIFT, PAGE_CACHE_SIZE);
+	if (pg->index > ((i_size_read(inode) - 1) >> PAGE_CACHE_SHIFT)) {
+		ret = 0;
+		memset(pg_buf, 0, PAGE_CACHE_SIZE);
+	} else {
+		ret = jffs2_read_inode_range(c, f, pg_buf,
+			pg->index << PAGE_CACHE_SHIFT, PAGE_CACHE_SIZE);
+	}
 
 	if (ret) {
 		ClearPageUptodate(pg);
-- 
1.6.3.3