Re: [PATCH 2.5.73] Signal stack fixes #1 introduce PF_SS_ACTIVE

[Paul Mackerras]

Jörn Engel writes:

> The problem is with a broken signal handler, that moves the stack
> pointer to nirvana.  You get a signal, set up the signal stack, move
> the pointer to nirvana, get a signal, set up the signal stack, move
> the pointer to nirvana, get a signal, ...

You can get the same effect by doing kill(0, SIGINT) inside a handler
for SIGINT.  All you seem to be saying is "if you behave stupidly then
bad things happen to you".  I don't see that this example exposes any
bug or vulnerability in the kernel.

> If I was just going down the signal stack, I would be perfectly happy,
> but instead the kernel believes each signal is the very first on the
> signal stack and sets it up again (and again...) each time.

You had to go to some trouble to get this effect - you had to use an
asm statement to change the stack pointer, which is well and truly
into "undefined behaviour" territory, and so you deserve all you
get. :)  It's a very contrived example IMHO.

Paul.