On Oct 28, 2009, at 10:01 AM, Christoph Baumann wrote:
On 28.10.2009 14:39, Allon Stern wrote:
What's the stack size of the SSH client?
Remember, the uclinux runtime does not have a dynamic stack size.
currently it's 32k
Run "<toolchain-prefix>flthdr" on your target FLAT executable to read
the header.
flthdr -s lets you change the stack size. Try increasing the stack
size.
Once you find an appropriate size, you can put it into the compile
flags.
Are there any "good" known values for ssh?
Well, stack usage varies according to program structure, as well as
call structure at runtime, so while static analysis can be a good
starting point, if there is any recursion, it becomes non-deterministic.
For security critical functions, like OpenSSH, I'd question whether a
non-mmu system is a good choice, especially without memory protection.
In any case, I'd recommend doubling the stack until you find a value
that works, then back off by powers of two until it doesn't, then back
up a couple of steps as a safety margin. Or, depending on how memory-
rich you are, you can just leave it with a bunch of extra memory. So
if 64K works, give it 128K of stack, for a good safety margin (which
is still no guarantee you won't be vulnerable to a stack overflow).
-
allon
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