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SubjectRe: [PATCH v3 0/5] Enable -Warray-bounds and -Wzero-length-bounds
On Mon, Aug 30, 2021 at 11:44:54AM -0700, Nathan Chancellor wrote:
> arch/powerpc/kernel/signal_32.c:780:2: error: array index 3 is past the end of the array (which contains 1 element) [-Werror,-Warray-bounds]
> unsafe_put_sigset_t(&frame->uc.uc_sigmask, oldset, failed);
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Or is this a Clang DCE failure?

#define unsafe_put_compat_sigset(compat, set, label) do { \
compat_sigset_t __user *__c = compat; \
const sigset_t *__s = set; \
\
switch (_NSIG_WORDS) { \
case 4: \
unsafe_put_user(__s->sig[3] >> 32, &__c->sig[7], label); \
unsafe_put_user(__s->sig[3], &__c->sig[6], label); \
fallthrough; \
case 3: \
unsafe_put_user(__s->sig[2] >> 32, &__c->sig[5], label); \
unsafe_put_user(__s->sig[2], &__c->sig[4], label); \
fallthrough; \
case 2: \
unsafe_put_user(__s->sig[1] >> 32, &__c->sig[3], label); \
unsafe_put_user(__s->sig[1], &__c->sig[2], label); \
fallthrough; \
case 1: \
unsafe_put_user(__s->sig[0] >> 32, &__c->sig[1], label); \
unsafe_put_user(__s->sig[0], &__c->sig[0], label); \
} \
} while (0)

if "set" has only 1 element, then _NSIG_WORDS must be 1. The warnings
are coming from cases 4 and 3. (But why not 2, which would also access
beyond the end?)

--
Kees Cook

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