liblzma: make dlopen()-based liblzma2 compatibility optional
Suppose I want to build a statically linked program:
gcc -static -o app app.c -lrpm -llzma
Suppose further that librpm.a was built against a pre-5.0 version of
liblzma so it does not allocate as much space for reserved fields at
the end of lzma_stream as the current API requires.
(This is a hypothetical scenario --- Debian librpm does not provide a
static library.)
If liblzma uses unpatched lzma_code() from XZ Utils >= 5.0, then
during calls to librpm that try to compress or decompress an
xz-compressed RPM, lzma_code’s reserved field checks will overflow the
buffer and segfault.
If liblzma uses the modified version of lzma_code() which asks libdl
if liblzma.so.2 is resident and refrains from checking reserved fields
past the end of the old lzma_stream struct when the answer is "yes",
the behavior is no better. The dynamic library liblzma.so.2 is _not_
resident, so lzma_code() dutifully reads reserved fields past the end
of the buffer --- segfault.
So the only safe behavior in the static library is to unconditionally
disable checks that might break for callers we want to continue to
support.
The new "./configure --enable-liblzma2-compat" option implements all
three sets of semantics:
- "./configure --disable-liblzma2-compat" means to check the full set
of reserved fields unconditionally. You can use this to check how
your application would behave with the unpatched library.
- "./configure --enable-liblzma2-compat=auto" means to skip checks of
reserved fields past the old end of struct lzma_stream when
liblzma.so.2 is resident. If a DSO built against liblzma2 shares
the process image, the ABI-incompatible checks are skipped for
safety, whereas in the usual case when no such DSO is resident, the
full set of checks is run to help application developers remember
to zero all reserved fields.
- "./configure --enable-liblzma2-compat" makes liblzma skip the
ABI-incompatible checks unconditionallty. You can use this if you
want your copy of liblzma to be usable by static libraries that
were built against the old library.
Patch-Name: liblzma-make-dlopen-based-liblzma2-compatibility-opt.patch
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
diff --git a/configure.ac b/configure.ac
index 6dae0b9..d17629e 100644
--- a/configure.ac
+++ b/configure.ac
@@ -548,10 +548,39 @@
esac
AM_CONDITIONAL([COND_THREADS], [test "x$enable_threads" != xno])
-# As a Debian-specific hack, liblzma uses dlopen() to check if extra
+# As a Debian-specific hack, liblzma can use dlopen() to check if extra
# paranoia is needed because unversioned symbols from liblzma.so.2 are
# present in the same process. See src/liblzma/common/common.c.
-AC_SEARCH_LIBS([dlopen], [dl])
+AC_MSG_CHECKING([if lzma_code checks should be relaxed for compatibility])
+AC_ARG_ENABLE([liblzma2-compat], [AC_HELP_STRING([--enable-liblzma2-compat],
+ [Relax run-time checks to accomodate old binaries built
+ with smaller sizeof(lzma_stream). The default is "dynamic",
+ which means to only use the relaxed checks when the dynamic
+ loader reports that liblzma.so.2 is loaded in the same process.])],
+ [], [enable_liblzma2_compat=dynamic])
+case $enable_liblzma2_compat in
+dynamic)
+ AC_SEARCH_LIBS([dlopen], [dl])
+ AC_DEFINE([LIBLZMA2_COMPAT_DYNAMIC], [1],
+ [Define to 1 to use dlopen() to check if lzma_code() checks
+ should be more tolerant because the process is also linked to
+ liblzma from Debian 6.0.])
+ AC_MSG_RESULT([auto])
+ ;;
+yes)
+ AC_DEFINE([LIBLZMA2_COMPAT], [1],
+ [Define to 1 to unconditionally make lzma_code() checks tolerant
+ to accomodate callers built against liblzma from Debian 6.0.])
+ AC_MSG_RESULT([yes])
+ ;;
+no)
+ AC_MSG_RESULT([no])
+ ;;
+*)
+ AC_MSG_RESULT([])
+ AC_MSG_ERROR([--enable-liblzma2: unrecognized value $enable_liblzma2_compat])
+ ;;
+esac
echo
echo "Initializing Libtool:"
diff --git a/src/liblzma/common/common.c b/src/liblzma/common/common.c
index 5474211..79427b0 100644
--- a/src/liblzma/common/common.c
+++ b/src/liblzma/common/common.c
@@ -164,16 +164,46 @@
// External to internal API wrapper //
//////////////////////////////////////
-static bool
-liblzma2_loaded(void)
+#ifdef LIBLZMA2_COMPAT_DYNAMIC
+
+static void
+init_liblzma2_compat(lzma_stream *strm)
{
void *handle = dlopen("liblzma.so.2", RTLD_LAZY | RTLD_NOLOAD);
if (handle) {
dlclose(handle);
- return true;
+ strm->internal->liblzma2_compat = true;
+ return;
}
+ strm->internal->liblzma2_compat = false;
+}
+
+static bool
+liblzma2_loaded(lzma_stream *strm)
+{
+ return strm->internal->liblzma2_compat;
+}
+
+#else
+
+static void
+init_liblzma2_compat(lzma_stream *strm)
+{
+}
+
+#ifdef LIBLZMA2_COMPAT
+static bool liblzma2_loaded(lzma_stream *strm)
+{
+ return true;
+}
+#else
+static bool liblzma2_loaded(lzma_stream *strm)
+{
return false;
}
+#endif
+
+#endif
extern lzma_ret
lzma_strm_init(lzma_stream *strm)
@@ -188,7 +218,7 @@
return LZMA_MEM_ERROR;
strm->internal->next = LZMA_NEXT_CODER_INIT;
- strm->internal->liblzma2_compat = liblzma2_loaded();
+ init_liblzma2_compat(strm);
}
memzero(strm->internal->supported_actions,
@@ -241,7 +271,7 @@
|| strm->reserved_ptr4 != NULL)
return LZMA_OPTIONS_ERROR;
- if (strm->internal->liblzma2_compat)
+ if (liblzma2_loaded(strm))
; /* Enough checks. */
else if (strm->reserved_int1 != 0
|| strm->reserved_int2 != 0
diff --git a/src/liblzma/common/common.h b/src/liblzma/common/common.h
index b056e41..eb1d052 100644
--- a/src/liblzma/common/common.h
+++ b/src/liblzma/common/common.h
@@ -227,9 +227,11 @@
/// made (no input consumed and no output produced by next.code).
bool allow_buf_error;
+#ifdef LIBLZMA2_COMPAT_DYNAMIC
/// Indicates whether we are sharing a process image with
/// liblzma.so.2 and need to tread carefully.
bool liblzma2_compat;
+#endif
};
