Fix use-after-free in BaseObjects destructor - #335
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amir-al-mohamad wants to merge 1 commit into
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~BaseObjects() called clear() on the derived class's String buffers after they had already been destroyed; with GCC -O2 they still hold the freed pointer, so String::remove() wrote into freed memory.
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I was chasing random heap corruption panics on an ESP32-S3 (arduino-esp32 3.x,
IDF 5.5.4) that showed up a few seconds after every Messaging::send(), usually
as tlsf asserts in the wifi or lwip tasks. With comprehensive heap poisoning
the checker reported a single zeroed byte at the start of 3-6 freed blocks
right after my Messages::Message / Notification objects went out of scope, and
a free() journal traced every one of those blocks to BaseO8::~BaseO8 and
BaseO4::~BaseO4.
The cause is in BaseObjects:
bufferspoints at theString buf[N]array ofthe derived class, and ~BaseObjects() calls clear() on it. By then the derived
members are already destroyed. GCC at -O2 drops the stores made by the inlined
~String() (dead stores into a dying object), so the Strings still hold the
freed pointer and length, and String::remove(0, len) writes a NUL into freed
memory.
Removing the clear() call from the destructor fixes it, the String members
clean up after themselves anyway. Before the change the heap got corrupted in
5 out of 5 test runs, after it in 0 out of 6.