[PATCH] grow_buffers() infinite loop fix

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>

1 files changed, 19 insertions, 2 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index eeb8ac1aa856..2a7828c0e59b 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1042,8 +1042,21 @@ grow_buffers(struct block_device *bdev, sector_t block, int size)
         } 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)
@@ -1070,12 +1083,16 @@ __getblk_slow(struct block_device *bdev, sector_t block, int size)
 
         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();
         }
 }