hfs: fix a potential buffer overflow

A specially-crafted Hierarchical File System (HFS) filesystem could cause
a buffer overflow to occur in a process's kernel stack during a memcpy()
call within the hfs_bnode_read() function (at fs/hfs/bnode.c:24).  The
attacker can provide the source buffer and length, and the destination
buffer is a local variable of a fixed length.  This local variable (passed
as "&entry" from fs/hfs/dir.c:112 and allocated on line 60) is stored in
the stack frame of hfs_bnode_read()'s caller, which is hfs_readdir().
Because the hfs_readdir() function executes upon any attempt to read a
directory on the filesystem, it gets called whenever a user attempts to
inspect any filesystem contents.

[amwang@redhat.com: modify this patch and fix coding style problems]
Signed-off-by: WANG Cong <amwang@redhat.com>
Cc: Eugene Teo <eteo@redhat.com>
Cc: Roman Zippel <zippel@linux-m68k.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Dave Anderson <anderson@redhat.com>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/hfs/catalog.c

@@ -289,6 +289,10 @@ int hfs_cat_move(u32 cnid, struct inode *src_dir, struct qstr *src_name,
 	err = hfs_brec_find(&src_fd);
 	if (err)
 		goto out;
+	if (src_fd.entrylength > sizeof(entry) || src_fd.entrylength < 0) {
+		err = -EIO;
+		goto out;
+	}
 
 	hfs_bnode_read(src_fd.bnode, &entry, src_fd.entryoffset,
 			    src_fd.entrylength);

fs/hfs/dir.c

@@ -79,6 +79,11 @@ static int hfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 		filp->f_pos++;
 		/* fall through */
 	case 1:
+		if (fd.entrylength > sizeof(entry) || fd.entrylength < 0) {
+			err = -EIO;
+			goto out;
+		}
+
 		hfs_bnode_read(fd.bnode, &entry, fd.entryoffset, fd.entrylength);
 		if (entry.type != HFS_CDR_THD) {
 			printk(KERN_ERR "hfs: bad catalog folder thread\n");
@@ -109,6 +114,12 @@ static int hfs_readdir(struct file *filp, void *dirent, filldir_t filldir)
 			err = -EIO;
 			goto out;
 		}
+
+		if (fd.entrylength > sizeof(entry) || fd.entrylength < 0) {
+			err = -EIO;
+			goto out;
+		}
+
 		hfs_bnode_read(fd.bnode, &entry, fd.entryoffset, fd.entrylength);
 		type = entry.type;
 		len = hfs_mac2asc(sb, strbuf, &fd.key->cat.CName);

fs/hfs/super.c

@@ -409,8 +409,13 @@ static int hfs_fill_super(struct super_block *sb, void *data, int silent)
 	/* try to get the root inode */
 	hfs_find_init(HFS_SB(sb)->cat_tree, &fd);
 	res = hfs_cat_find_brec(sb, HFS_ROOT_CNID, &fd);
-	if (!res)
+	if (!res) {
+		if (fd.entrylength > sizeof(rec) || fd.entrylength < 0) {
+			res =  -EIO;
+			goto bail;
+		}
 		hfs_bnode_read(fd.bnode, &rec, fd.entryoffset, fd.entrylength);
+	}
 	if (res) {
 		hfs_find_exit(&fd);
 		goto bail_no_root;