freevxfs: refactor readdir and lookup code

This change fixes also a buffer overflow which was caused by
accessing address space beyond mapped page
Signed-off-by: Krzysztof Błaszkowski <kb@sysmikro.com.pl>
Signed-off-by: Christoph Hellwig <hch@lst.de>

fs/freevxfs/vxfs_lookup.c

@@ -62,35 +62,6 @@ const struct file_operations vxfs_dir_operations = {
 	.iterate_shared =	vxfs_readdir,
 };
 
-static inline u_long
-dir_blocks(struct inode *ip)
-{
-	u_long			bsize = ip->i_sb->s_blocksize;
-	return (ip->i_size + bsize - 1) & ~(bsize - 1);
-}
-
-/*
- * NOTE! unlike strncmp, vxfs_match returns 1 for success, 0 for failure.
- *
- * len <= VXFS_NAMELEN and de != NULL are guaranteed by caller.
- */
-static inline int
-vxfs_match(struct vxfs_sb_info *sbi, int len, const char *const name,
-		struct vxfs_direct *de)
-{
-	if (len != fs16_to_cpu(sbi, de->d_namelen))
-		return 0;
-	if (!de->d_ino)
-		return 0;
-	return !memcmp(name, de->d_name, len);
-}
-
-static inline struct vxfs_direct *
-vxfs_next_entry(struct vxfs_sb_info *sbi, struct vxfs_direct *de)
-{
-	return ((struct vxfs_direct *)
-		((char *)de + fs16_to_cpu(sbi, de->d_reclen)));
-}
 
 /**
  * vxfs_find_entry - find a mathing directory entry for a dentry
@@ -109,53 +80,64 @@ vxfs_next_entry(struct vxfs_sb_info *sbi, struct vxfs_direct *de)
 static struct vxfs_direct *
 vxfs_find_entry(struct inode *ip, struct dentry *dp, struct page **ppp)
 {
-	struct vxfs_sb_info		*sbi = VXFS_SBI(ip->i_sb);
-	u_long				npages, page, nblocks, pblocks, block;
 	u_long bsize = ip->i_sb->s_blocksize;
 	const char *name = dp->d_name.name;
 	int namelen = dp->d_name.len;
+	loff_t limit = VXFS_DIRROUND(ip->i_size);
+	struct vxfs_direct *de_exit = NULL;
+	loff_t pos = 0;
+	struct vxfs_sb_info *sbi = VXFS_SBI(ip->i_sb);
 
-	npages = dir_pages(ip);
-	nblocks = dir_blocks(ip);
-	pblocks = VXFS_BLOCK_PER_PAGE(ip->i_sb);
-	
-	for (page = 0; page < npages; page++) {
-		caddr_t			kaddr;
+	while (pos < limit) {
 		struct page *pp;
+		char *kaddr;
+		int pg_ofs = pos & ~PAGE_MASK;
 
-		pp = vxfs_get_page(ip->i_mapping, page);
+		pp = vxfs_get_page(ip->i_mapping, pos >> PAGE_SHIFT);
 		if (IS_ERR(pp))
-			continue;
-		kaddr = (caddr_t)page_address(pp);
+			return NULL;
+		kaddr = (char *)page_address(pp);
 
-		for (block = 0; block <= nblocks && block <= pblocks; block++) {
-			caddr_t			baddr, limit;
-			struct vxfs_dirblk	*dbp;
+		while (pg_ofs < PAGE_SIZE && pos < limit) {
 			struct vxfs_direct *de;
 
-			baddr = kaddr + (block * bsize);
-			limit = baddr + bsize - VXFS_DIRLEN(1);
+			if ((pos & (bsize - 1)) < 4) {
+				struct vxfs_dirblk *dbp =
+					(struct vxfs_dirblk *)
+					 (kaddr + (pos & ~PAGE_MASK));
+				int overhead = VXFS_DIRBLKOV(sbi, dbp);
 
-			dbp = (struct vxfs_dirblk *)baddr;
-			de = (struct vxfs_direct *)
-				(baddr + VXFS_DIRBLKOV(sbi, dbp));
+				pos += overhead;
+				pg_ofs += overhead;
+			}
+			de = (struct vxfs_direct *)(kaddr + pg_ofs);
 
-			for (; (caddr_t)de <= limit;
-					de = vxfs_next_entry(sbi, de)) {
-				if (!de->d_reclen)
+			if (!de->d_reclen) {
+				pos += bsize - 1;
+				pos &= ~(bsize - 1);
 				break;
+			}
+
+			pg_ofs += fs16_to_cpu(sbi, de->d_reclen);
+			pos += fs16_to_cpu(sbi, de->d_reclen);
 			if (!de->d_ino)
 				continue;
-				if (vxfs_match(sbi, namelen, name, de)) {
+
+			if (namelen != fs16_to_cpu(sbi, de->d_namelen))
+				continue;
+			if (!memcmp(name, de->d_name, namelen)) {
 				*ppp = pp;
-					return (de);
-				}
+				de_exit = de;
+				break;
 			}
 		}
+		if (!de_exit)
 			vxfs_put_page(pp);
+		else
+			break;
 	}
 
-	return NULL;
+	return de_exit;
 }
 
 /**
@@ -238,80 +220,81 @@ vxfs_readdir(struct file *fp, struct dir_context *ctx)
 {
 	struct inode		*ip = file_inode(fp);
 	struct super_block	*sbp = ip->i_sb;
-	struct vxfs_sb_info	*sbi = VXFS_SBI(sbp);
 	u_long			bsize = sbp->s_blocksize;
-	u_long			page, npages, block, pblocks, nblocks, offset;
-	loff_t			pos;
-
+	loff_t			pos, limit;
+	struct vxfs_sb_info	*sbi = VXFS_SBI(sbp);
 
 	if (ctx->pos == 0) {
 		if (!dir_emit_dot(fp, ctx))
-			return 0;
-		ctx->pos = 1;
+			goto out;
+		ctx->pos++;
 	}
 	if (ctx->pos == 1) {
 		if (!dir_emit(ctx, "..", 2, VXFS_INO(ip)->vii_dotdot, DT_DIR))
-			return 0;
-		ctx->pos = 2;
+			goto out;
+		ctx->pos++;
 	}
-	pos = ctx->pos - 2;
 
-	if (pos > VXFS_DIRROUND(ip->i_size))
-		return 0;
-
-	npages = dir_pages(ip);
-	nblocks = dir_blocks(ip);
-	pblocks = VXFS_BLOCK_PER_PAGE(sbp);
+	limit = VXFS_DIRROUND(ip->i_size);
+	if (ctx->pos > limit)
+		goto out;
 
-	page = pos >> PAGE_SHIFT;
-	offset = pos & ~PAGE_MASK;
-	block = (u_long)(pos >> sbp->s_blocksize_bits) % pblocks;
+	pos = ctx->pos & ~3L;
 
-	for (; page < npages; page++, block = 0) {
-		char			*kaddr;
+	while (pos < limit) {
 		struct page *pp;
+		char *kaddr;
+		int pg_ofs = pos & ~PAGE_MASK;
+		int rc = 0;
 
-		pp = vxfs_get_page(ip->i_mapping, page);
+		pp = vxfs_get_page(ip->i_mapping, pos >> PAGE_SHIFT);
 		if (IS_ERR(pp))
-			continue;
+			return -ENOMEM;
+
 		kaddr = (char *)page_address(pp);
 
-		for (; block <= nblocks && block <= pblocks; block++) {
-			char			*baddr, *limit;
-			struct vxfs_dirblk	*dbp;
+		while (pg_ofs < PAGE_SIZE && pos < limit) {
 			struct vxfs_direct *de;
 
-			baddr = kaddr + (block * bsize);
-			limit = baddr + bsize - VXFS_DIRLEN(1);
+			if ((pos & (bsize - 1)) < 4) {
+				struct vxfs_dirblk *dbp =
+					(struct vxfs_dirblk *)
+					 (kaddr + (pos & ~PAGE_MASK));
+				int overhead = VXFS_DIRBLKOV(sbi, dbp);
 
-			dbp = (struct vxfs_dirblk *)baddr;
-			de = (struct vxfs_direct *)
-				(offset ?
-				 (kaddr + offset) :
-				 (baddr + VXFS_DIRBLKOV(sbi, dbp)));
+				pos += overhead;
+				pg_ofs += overhead;
+			}
+			de = (struct vxfs_direct *)(kaddr + pg_ofs);
 
-			for (; (char *)de <= limit;
-					de = vxfs_next_entry(sbi, de)) {
-				if (!de->d_reclen)
+			if (!de->d_reclen) {
+				pos += bsize - 1;
+				pos &= ~(bsize - 1);
 				break;
+			}
+
+			pg_ofs += fs16_to_cpu(sbi, de->d_reclen);
+			pos += fs16_to_cpu(sbi, de->d_reclen);
 			if (!de->d_ino)
 				continue;
 
-				offset = (char *)de - kaddr;
-				ctx->pos = ((page << PAGE_SHIFT) | offset) + 2;
-				if (!dir_emit(ctx, de->d_name,
+			rc = dir_emit(ctx, de->d_name,
 					fs16_to_cpu(sbi, de->d_namelen),
 					fs32_to_cpu(sbi, de->d_ino),
-						DT_UNKNOWN)) {
-					vxfs_put_page(pp);
-					return 0;
-				}
+					DT_UNKNOWN);
+			if (!rc) {
+				/* the dir entry was not read, fix pos. */
+				pos -= fs16_to_cpu(sbi, de->d_reclen);
+				break;
 			}
-			offset = 0;
 		}
 		vxfs_put_page(pp);
-		offset = 0;
+		if (!rc)
+			break;
 	}
-	ctx->pos = ((page << PAGE_SHIFT) | offset) + 2;
+
+	ctx->pos = pos | 2;
+
+out:
 	return 0;
 }