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libthread: fix use after free of first thread in each proc

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This was causing sporadic but frequent crashes at startup
in 9pserve on the new M1 Macs, correctly diagnosing a
use-after-free.
This commit is contained in:
Russ Cox 2020-12-15 00:05:17 -05:00
parent a012d17433
commit 2991442aef
1 changed files with 9 additions and 1 deletions
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10
src/libthread/thread.c
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@ -411,7 +411,14 @@ Top:
p->nthread--;
/*print("nthread %d\n", p->nthread); */
_threadstkfree(t->stk, t->stksize);
free(t);
/*
* Cannot free p->thread0 yet: it is used for the
* context switches back to the scheduler.
* Instead, we will free it at the end of this function.
* But all the other threads can be freed now.
*/
if(t != p->thread0)
free(t);
}
for(;;){
@ -490,6 +497,7 @@ Out:
unlock(&threadnproclock);
unlock(&p->lock);
_threadsetproc(nil);
free(p->thread0);
free(p);
_threadpexit();
}