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>

1 files changed, 11 insertions, 0 deletions

diff --git a/fs/hfs/dir.c b/fs/hfs/dir.c
index 7c69b98a2e45..2b3b8611b41b 100644
--- a/fs/hfs/dir.c
+++ b/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);