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fctx_decreference() may call fctx_destroy(), which in turn may free the
fetch context by calling isc_mem_putanddetach(). This means that
whenever fctx_decreference() is called, the fetch context pointer should
be assumed to point to garbage after that call. Meanwhile, the
following pattern is used in several places in lib/dns/resolver.c:
LOCK(&res->buckets[fctx->bucketnum].lock);
bucket_empty = fctx_decreference(fctx);
UNLOCK(&res->buckets[fctx->bucketnum].lock);
Given that 'fctx' may be freed by the fctx_decreference() call, there is
no guarantee that the value of fctx->bucketnum will be the same before
and after the fctx_decreference() call. This can cause all kinds of
locking issues as LOCK() calls no longer match up with their UNLOCK()
counterparts.
Fix by always using a helper variable to hold the bucket number when the
pattern above is used.
Note that fctx_try() still uses 'fctx' after calling fctx_decreference()
(it calls fctx_done()). This is safe to do because the reference count
for 'fctx' is increased a few lines earlier and it also cannot be zero
right before that increase happens, so the fctx_decreference() call in
that particular location never invokes fctx_destroy(). Nevertheless,
use a helper variable for that call site as well, to retain consistency
and to prevent copy-pasted code from causing similar problems in the
future.
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| .. | ||
| bind9 | ||
| dns | ||
| irs | ||
| isc | ||
| isccc | ||
| isccfg | ||
| ns | ||
| win32/bindevt | ||
| .gitignore | ||
| Kyuafile | ||
| Makefile.in | ||