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Subject[patch 07/18] grow_buffers() infinite loop fix (CVE-2006-5757, CVE-2006-6060)
-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Andrew Morton <akpm@osdl.org>
If grow_buffers() is for some reason passed a block number which wants to lie
outside the maximum-addressable pagecache range (PAGE_SIZE * 4G bytes) then it
will accidentally truncate `index' and will then instnatiate a page at the
wrong pagecache offset. This causes __getblk_slow() to go into an infinite
loop.

This can happen with corrupted disks, or with software errors elsewhere.

Detect that, and handle it.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/buffer.c | 21 +++++++++++++++++++--
1 file changed, 19 insertions(+), 2 deletions(-)
--- linux-2.6.18.7.orig/fs/buffer.c
+++ linux-2.6.18.7/fs/buffer.c
@@ -1179,8 +1179,21 @@ grow_buffers(struct block_device *bdev,
} while ((size << sizebits) < PAGE_SIZE);

index = block >> sizebits;
- block = index << sizebits;

+ /*
+ * Check for a block which wants to lie outside our maximum possible
+ * pagecache index. (this comparison is done using sector_t types).
+ */
+ if (unlikely(index != block >> sizebits)) {
+ char b[BDEVNAME_SIZE];
+
+ printk(KERN_ERR "%s: requested out-of-range block %llu for "
+ "device %s\n",
+ __FUNCTION__, (unsigned long long)block,
+ bdevname(bdev, b));
+ return -EIO;
+ }
+ block = index << sizebits;
/* Create a page with the proper size buffers.. */
page = grow_dev_page(bdev, block, index, size);
if (!page)
@@ -1207,12 +1220,16 @@ __getblk_slow(struct block_device *bdev,

for (;;) {
struct buffer_head * bh;
+ int ret;

bh = __find_get_block(bdev, block, size);
if (bh)
return bh;

- if (!grow_buffers(bdev, block, size))
+ ret = grow_buffers(bdev, block, size);
+ if (ret < 0)
+ return NULL;
+ if (ret == 0)
free_more_memory();
}
}
--
-
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