[BUG][SECURITY] Kernel stack overflow in hfs_mac2asc()

[Clement LECIGNE <clemun@gmail.com>]

Hi lkml,

I have found there is no len nor bound checkings in hfs_mac2asc()
function against the size of the out buffer passed as parameter.
The src size can be greater than HFS_MAX_NAMELEN on malformed file
system. HFS_MAX_NAMELEN is 31 whereas src size can be set up to
255 (unsigned char).

This can lead to a basic kernel stack overflow with user controlled
data through for example hfs_readdir() which calls hfs_mac2asc() with
out buffer "allocated" on the stack.

This overflow can be simply fixed by adding bound checks on srclen
before doing the copy.

Best regards,

-- 
Clément LECIGNE,
"In Python, how do you create a string of random characters? Read a Perl
file!"