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Re: Consensus on MT-, AS- and AC-Safety docs.

On 11/27/2013 02:34 PM, Joseph S. Myers wrote:
On Wed, 27 Nov 2013, Florian Weimer wrote:
I think we should do that in the code that wraps the signal handler call, to
address this class of errors once and for all.  Is this feasible?

On many architectures the signal trampoline is provided by the kernel and
so has no access to libc implementation details like errno.  As far as I
understand, even when provided by libc all it does is call the sigreturn
syscall and provide appropriate unwind information for the registers the
kernel saved on the stack - that is, there is no userspace code called
before the signal handler that would have a chance to save errno.

The number of signals is fixed and small, so it should be feasible to install our own handler in the kernel and store the user-supplied handler in a lookup table that gets called from our handler. There might be a slight performance impact, though.

But if we think this errno issue is serious, rather than patching almost any signal handler out there right now, we should address it in glibc.

Florian Weimer / Red Hat Product Security Team

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