Hi Rusty,
I was looking at the diff between kernel v3.12 and recent master (after
3.13-rc7),
and noticed that in the following commit:
commit 94af3abf995b17f6a008b00152c94841242ec6c7
Author: Rusty Russell <ru...@rustcorp.com.au>
Date: Wed Nov 20 22:15:02 2013 +1100
powerpc: ELF2 binaries launched directly.
on powerpc, those lines appear in start_thread():
+ /* start is a relocated pointer to the function
+ * descriptor for the elf _start routine. The first
+ * entry in the function descriptor is the entry
+ * address of _start and the second entry is the TOC
+ * value we need to use.
+ */
+ __get_user(entry, (unsigned long __user *)start);
+ __get_user(toc, (unsigned long __user *)start+1);
Note the "__" before get_user(), which bypass any kind of validation on the
addresses.
Amongst the callers, if we look at fs/binfmt_elf.c:load_elf_binary(), we see:
elf_entry = loc->elf_ex.e_entry;
if (BAD_ADDR(elf_entry)) {
force_sig(SIGSEGV, current);
retval = -EINVAL;
goto out_free_dentry;
}
and the elf_entry gets passed to start_thread().
If we craft a binary with elf_entry address of
TASK_SIZE - 1 (1 byte before TASK_SIZE), then I think we could make both
__get_user() calls access data beyond TASK_SIZE, because elf_entry address
is verified, but there is no validation on its range AFAIU. Is it expected ?
Am I missing something ?
Thanks,
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
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