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599c1d2a6b
From an attacker's point of view, a VLA declaration is essentially a
primitive for performing arbitrary arithmetic on the stack pointer. If
the attacker can control the size of a VLA they have a very powerful
tool for causing memory corruption.
To mitigate this kind of attack, and the more general class of stack
clash vulnerabilities, C compilers insert extra code when allocating a
VLA to probe the growing stack one page at a time. If these probes hit
the stack guard page, the program will crash.
From the point of view of a C programmer, there are a few things to
consider about VLAs:
* If it is important to handle allocation failures in a controlled
manner, don't use VLAs. You can use VLAs if it is OK for
unreasonable inputs to cause an uncontrolled crash.
* If the VLA is known to be smaller than some known fixed size,
use a fixed size array and a run-time check to ensure it is large
enough. This will be more efficient than the compiler's stack
probes that need to cope with arbitrary-size VLAs.
* If the VLA might be large, allocate it on the heap. The heap
allocator can allocate multiple pages in one shot, whereas the
stack clash probes work one page at a time.
Most of the existing uses of VLAs in BIND are in test code where they
are benign, but there was one instance in `named`, in the GSS-TSIG
verification code, which has now been removed.
This commit adjusts the style guide and the C compiler flags to allow
VLAs in test code but not elsewhere.
36 lines
534 B
Makefile
36 lines
534 B
Makefile
include $(top_srcdir)/Makefile.top
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SUBDIRS = system
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noinst_PROGRAMS = \
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test_client \
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test_server \
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wire_test
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AM_CFLAGS += \
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$(TEST_CFLAGS)
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test_client_CPPFLAGS = \
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$(AM_CPPFLAGS) \
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$(LIBISC_CFLAGS)
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test_client_LDADD = \
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$(LIBISC_LIBS) \
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$(LIBDNS_LIBS)
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test_server_CPPFLAGS = \
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$(AM_CPPFLAGS) \
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$(LIBISC_CFLAGS)
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test_server_LDADD = \
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$(LIBISC_LIBS) \
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$(LIBDNS_LIBS)
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wire_test_CPPFLAGS = \
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$(AM_CPPFLAGS) \
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$(LIBISC_CFLAGS) \
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$(LIBDNS_CFLAGS)
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wire_test_LDADD = \
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$(LIBISC_LIBS) \
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$(LIBDNS_LIBS)
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