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<div class="moz-cite-prefix">Am 30.01.26 um 17:33 schrieb Simon
Kelley:<br>
</div>
<blockquote type="cite"
cite="mid:88b1f061-f8f2-48be-94fd-9574db1fddf6@thekelleys.org.uk">I
just sent SIGHUP twice in succession to the dnsmasq process in my
OpenWRT router, with the new malloc-logging feature enabled.
<br>
<br>
HUP frees a load of configuration and the re-reads it and I
correlated all the memory freed by the second HUP with what was
allocated in the first HUP.
<br>
<br>
It's perfect. Every block is freed.
<br>
<br>
<br>
This is a fairly old installation, so old libraries, etc, but the
very latest dnsmasq code.
<br>
<br>
The configuration it's re-reading is pretty small.
<br>
<br>
I then tried your technique of hitting dnsmasq hard with many
HUPs.
<br>
<br>
I had to go up to half a million to see much effect, but I guess
most of those were dropped since they will have arrived before the
previous one was cleared.
<br>
<br>
In any case I could see a reproducible rise of a few percent in
the VSZ of the process each time.
<br>
<br>
What's clear is that the configuration is stored in a _lot_ of
small allocations, so re-reading a substantial configuration will
free a lot of small blocks and then malloc a lot of small blocks.
<br>
<br>
A quick Google produces some complaints about the fragmentation
performance of musl, which may be significant.
<br>
<br>
Is your installation using musl as the C library, and is it
possible to build dnsmasq against, say glibc to test?
<br>
<br>
Nearly all of the memory management on dnsmasq that gets hit by
answering DNS or DHCP requests avoid hammering the malloc system
by building pools of free data structures that get re-cycled as
needed. Once the pools have grown to equilibrium size, even a very
busy server hardly uses the heap. I guess the configuration code
to use the same policy, but it's a big re-write, and re-reading
configuration on a sub-second timescale is an unlikely use-case.
<br>
<br>
</blockquote>
<p>I've built dnsmasq v2.93test2 on Fedora Linux 43 (amd64 aka
x86_64) with address and undefined behavior sanitizers in GCC and
with HAVE_DNSSEC, and I am providing three patches (should suit
git-am) to fix</p>
<p>* one access past the end of the iovec (reading past the iovcnt
limit) that triggers AddressSanitizer reproducibly, in
read_writev()</p>
<p>* one "variable may be used uninitialized" (I didn't check the
logic, I just bluntly added = NULL to shut up the compiler) in
dnssec code</p>
<p>* one patch that fixes undefined behavior, where base32_decode
may shift into the sign bit which might wreak havoc on perverse C
implementations (compiler & processor combination); I didn't
test if as alternative, making the "oc" an unsigned integer could
help, because for unsigned integers, wrapping is well-defined, but
not for signed integers. We can clear the "oc" when we've written
it.</p>
<p>I haven't seen a memory leak reported by address sanitizer yet,
also valgrind in leak-checking mode on FreeBSD didn't holler.</p>
<p>To reproduce, add #define HAVE_DNSSEC to src/config.h, and change
these three lines in Makefile - this assumes your debugger
understands DWARF4 format and the compiler is reasonably
compatible to GCC. You may need to tweak
ASAN_OPTIONS=detect_leaks=1 to enable leak checking. Note the leak
checker availability across operating systems is pretty limited.
Systems that don't have it want to forgo that and use a different
leak checker (valgrind might work).</p>
<p>
<blockquote type="cite"><span style="font-family:monospace"><span
style="color:#18b218;background-color:#ffffff;">CFLAGS
= -Wall -W -Og -ggdb3 -gdwarf-4
-fno-omit-frame-pointer</span><span
style="color:#000000;background-color:#ffffff;">
</span><br>
<span style="color:#18b218;background-color:#ffffff;">LDFLAGS
= -fsanitize=address,undefined</span><span
style="color:#000000;background-color:#ffffff;">
</span><br>
<span style="color:#18b218;background-color:#ffffff;">COPTS
= -fsanitize=address,undefined</span><br>
</span></blockquote>
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