Messages in this thread | | | Date | Wed, 23 Nov 2011 16:06:25 +0000 | From | Ian Abbott <> | Subject | Re: [PATCH] comedi: integer overflow in do_insnlist_ioctl() |
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On 2011-11-23 14:50, Dan Carpenter wrote: > On Wed, Nov 23, 2011 at 08:59:52AM -0500, Xi Wang wrote: >> Thanks for the pointer. However you cannot do the overflow check using >> >> if (sizeof(struct comedi_insn) * insnlist.n_insns < insnlist.n_insns) >> >> Let's assume 32-bit system, sizeof(struct comedi_insn) = 32, and >> insnlist.n_insns = 0x7fffffff. >> >> Note that 32 * 0x7fffffff = 0xffffffe0 overflows but bypasses your check. >> > > Argh... You're right, my check is wrong. What I like about my patch > though is that it doesn't introduce an arbitrary limit. Could you > redo your check without the MAX_INSNS?
Could use something like:
if (insnlist.n_insns <= ULONG_MAX / sizeof(struct comedi_insn)) insns = kmalloc(sizeof(struct comedi_insn) * insnlist.n_insns, GFP_KERNEL); if (!insns) ...
(note that insns is initialized to NULL).
-- -=( Ian Abbott @ MEV Ltd. E-mail: <abbotti@mev.co.uk> )=- -=( Tel: +44 (0)161 477 1898 FAX: +44 (0)161 718 3587 )=-
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