[PATCH] ufs: write to hole in big file

On UFS, this scenario:
	open(O_TRUNC)
	lseek(1024 * 1024 * 80)
	write("A")
	lseek(1024 * 2)
	write("A")

may cause access to invalid address.

This happened because of "goal" is calculated in wrong way in block
allocation path, as I see this problem exists also in 2.4.

We use construction like this i_data[lastfrag], i_data array of pointers to
direct blocks, indirect and so on, it has ceratain size ~20 elements, and
lastfrag may have value for example 40000.

Also this patch fixes related to handling such scenario issues, wrong
zeroing metadata, in case of block(not fragment) allocation, and wrong goal
calculation, when we allocate block

Signed-off-by: Evgeniy Dushistov <dushistov@mail.ru>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ufs/inode.c

@@ -169,18 +169,20 @@ static void ufs_clear_frag(struct inode *inode, struct buffer_head *bh)
 
 static struct buffer_head *
 ufs_clear_frags(struct inode *inode, sector_t beg,
-		unsigned int n)
+		unsigned int n, sector_t want)
 {
-	struct buffer_head *res, *bh;
+	struct buffer_head *res = NULL, *bh;
 	sector_t end = beg + n;
 
-	res = sb_getblk(inode->i_sb, beg);
-	ufs_clear_frag(inode, res);
-	for (++beg; beg < end; ++beg) {
+	for (; beg < end; ++beg) {
 		bh = sb_getblk(inode->i_sb, beg);
 		ufs_clear_frag(inode, bh);
-		brelse(bh);
+		if (want != beg)
+			brelse(bh);
+		else
+			res = bh;
 	}
+	BUG_ON(!res);
 	return res;
 }
 
@@ -265,7 +267,9 @@ repeat:
 			lastfrag = ufsi->i_lastfrag;
 			
 		}
-		goal = fs32_to_cpu(sb, ufsi->i_u1.i_data[lastblock]) + uspi->s_fpb;
+		tmp = fs32_to_cpu(sb, ufsi->i_u1.i_data[lastblock]);
+		if (tmp)
+			goal = tmp + uspi->s_fpb;
 		tmp = ufs_new_fragments (inode, p, fragment - blockoff, 
 					 goal, required + blockoff,
 					 err, locked_page);
@@ -277,13 +281,15 @@ repeat:
 		tmp = ufs_new_fragments(inode, p, fragment - (blockoff - lastblockoff),
 					fs32_to_cpu(sb, *p), required +  (blockoff - lastblockoff),
 					err, locked_page);
-	}
+	} else /* (lastblock > block) */ {
 	/*
 	 * We will allocate new block before last allocated block
 	 */
-	else /* (lastblock > block) */ {
-		if (lastblock && (tmp = fs32_to_cpu(sb, ufsi->i_u1.i_data[lastblock-1])))
-			goal = tmp + uspi->s_fpb;
+		if (block) {
+			tmp = fs32_to_cpu(sb, ufsi->i_u1.i_data[block-1]);
+			if (tmp)
+				goal = tmp + uspi->s_fpb;
+		}
 		tmp = ufs_new_fragments(inode, p, fragment - blockoff,
 					goal, uspi->s_fpb, err, locked_page);
 	}
@@ -296,7 +302,7 @@ repeat:
 	}
 
 	if (!phys) {
-		result = ufs_clear_frags(inode, tmp + blockoff, required);
+		result = ufs_clear_frags(inode, tmp, required, tmp + blockoff);
 	} else {
 		*phys = tmp + blockoff;
 		result = NULL;
@@ -383,7 +389,7 @@ repeat:
 		}
 	}
 
-	if (block && (tmp = fs32_to_cpu(sb, ((__fs32*)bh->b_data)[block-1]) + uspi->s_fpb))
+	if (block && (tmp = fs32_to_cpu(sb, ((__fs32*)bh->b_data)[block-1])))
 		goal = tmp + uspi->s_fpb;
 	else
 		goal = bh->b_blocknr + uspi->s_fpb;
@@ -397,7 +403,8 @@ repeat:
 
 
 	if (!phys) {
-		result = ufs_clear_frags(inode, tmp + blockoff, uspi->s_fpb);
+		result = ufs_clear_frags(inode, tmp, uspi->s_fpb,
+					 tmp + blockoff);
 	} else {
 		*phys = tmp + blockoff;
 		*new = 1;