Unable to insert kernel module: Unknown symbol net_namespace_list - linux-kernel

Question

I'm writing a kernel module that lists the network namespaces using the for_each_net and have written the following snippet which compiles fine:
rtnl_lock();
for_each_net(net)
printk("network ns: %p\n", net);
rtnl_unlock();
However when I try to insert the kernel module i get the following error:
insmod: ERROR: could not insert module kerNotification.ko: Unknown symbol in module
The dmesg gives the additional error information:
[3561461.418499] kerNotification: Unknown symbol net_namespace_list (err 0)
The kallsyms shows that it has the symbol of this kernel function:
[josh#dev kernel_prog(keystone_admin)]# cat /proc/kallsyms | grep net_namespace_list
ffffffff81a203e0 R __ksymtab_net_namespace_list
ffffffff81a32bc0 r __kcrctab_net_namespace_list
ffffffff81a55452 r __kstrtab_net_namespace_list
ffffffff81b6b000 D net_namespace_lis
The Module.symvers is included in the makefile as KBUILD_EXTRA_SYMBOLS. Here is the Makefile:
obj-m += kerNotification.o
SYMBOLA=/usr/src/kernels/4.4.57-1.el7.elrepo.x86_64/Module.symvers
KBUILD_EXTRA_SYMBOLS= $(SYMBOLA)
all:
make -C /lib/modules/$(shell uname -r)/build $(KBUILD_EXTRA_SYMBOLS) M=$(PWD) modules
clean:
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
Here is the complete logs when the make file is built with V=1:
make -C /lib/modules/4.4.57-1.el7.elrepo.x86_64/build /usr/src/kernels/4.4.57-1.el7.elrepo.x86_64/Module.symvers M=/home/cmmdocker/kernel_prog modules
make[1]: Entering directory `/usr/src/kernels/4.4.57-1.el7.elrepo.x86_64'
test -e include/generated/autoconf.h -a -e include/config/auto.conf || ( \
echo >&2; \
echo >&2 " ERROR: Kernel configuration is invalid."; \
echo >&2 " include/generated/autoconf.h or include/config/auto.conf are missing.";\
echo >&2 " Run 'make oldconfig && make prepare' on kernel src to fix it."; \
echo >&2 ; \
/bin/false)
make[1]: Nothing to be done for `/usr/src/kernels/4.4.57-1.el7.elrepo.x86_64/Module.symvers'.
mkdir -p /home/cmmdocker/kernel_prog/.tmp_versions ; rm -f /home/cmmdocker/kernel_prog/.tmp_versions/*
make -f ./scripts/Makefile.build obj=/home/cmmdocker/kernel_prog
rm -f /home/cmmdocker/kernel_prog/built-in.o; ar rcsD /home/cmmdocker/kernel_prog/built-in.o
gcc -Wp,-MD,/home/cmmdocker/kernel_prog/.kerNotification.o.d -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.8.5/include -I./arch/x86/include -Iarch/x86/include/generated/uapi -Iarch/x86/include/generated -Iinclude -I./arch/x86/include/uapi -Iarch/x86/include/generated/uapi -I./include/uapi -Iinclude/generated/uapi -include ./include/linux/kconfig.h -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -fno-PIE -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mpreferred-stack-boundary=3 -mtune=generic -mno-red-zone -mcmodel=kernel -funit-at-a-time -maccumulate-outgoing-args -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1 -DCONFIG_AS_FXSAVEQ=1 -DCONFIG_AS_SSSE3=1 -DCONFIG_AS_CRC32=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -fno-delete-null-pointer-checks -Wno-maybe-uninitialized -O2 --param=allow-store-data-races=0 -Wframe-larger-than=2048 -fstack-protector-strong -Wno-unused-but-set-variable -fno-omit-frame-pointer -fno-optimize-sibling-calls -fno-var-tracking-assignments -g -pg -mfentry -DCC_USING_FENTRY -fno-inline-functions-called-once -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -Werror=implicit-int -Werror=strict-prototypes -DCC_HAVE_ASM_GOTO -DMODULE -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(kerNotification)" -D"KBUILD_MODNAME=KBUILD_STR(kerNotification)" -c -o /home/cmmdocker/kernel_prog/.tmp_kerNotification.o /home/cmmdocker/kernel_prog/kerNotification.c
/home/cmmdocker/kernel_prog/kerNotification.c: In function ‘kerNotification_init’:
/home/cmmdocker/kernel_prog/kerNotification.c:37:5: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
struct net *net;
^
if [ "-pg" = "-pg" ]; then if [ /home/cmmdocker/kernel_prog/kerNotification.o != "scripts/mod/empty.o" ]; then ./scripts/recordmcount "/home/cmmdocker/kernel_prog/kerNotification.o"; fi; fi;
(cat /dev/null; echo kernel//home/cmmdocker/kernel_prog/kerNotification.ko;) > /home/cmmdocker/kernel_prog/modules.order
make -f ./scripts/Makefile.modpost
find /home/cmmdocker/kernel_prog/.tmp_versions -name '*.mod' | xargs -r grep -h '\.ko$' | sort -u | sed 's/\.ko$/.o/' | scripts/mod/modpost -m -a -i ./Module.symvers -I /home/cmmdocker/kernel_prog/Module.symvers -e /usr/src/kernels/4.4.57-1.el7.elrepo.x86_64/Module.symvers -o /home/cmmdocker/kernel_prog/Module.symvers -w -s -T -
gcc -Wp,-MD,/home/cmmdocker/kernel_prog/.kerNotification.mod.o.d -nostdinc -isystem /usr/lib/gcc/x86_64-redhat-linux/4.8.5/include -I./arch/x86/include -Iarch/x86/include/generated/uapi -Iarch/x86/include/generated -Iinclude -I./arch/x86/include/uapi -Iarch/x86/include/generated/uapi -I./include/uapi -Iinclude/generated/uapi -include ./include/linux/kconfig.h -D__KERNEL__ -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs -fno-strict-aliasing -fno-common -Werror-implicit-function-declaration -Wno-format-security -std=gnu89 -fno-PIE -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx -m64 -falign-jumps=1 -falign-loops=1 -mno-80387 -mno-fp-ret-in-387 -mpreferred-stack-boundary=3 -mtune=generic -mno-red-zone -mcmodel=kernel -funit-at-a-time -maccumulate-outgoing-args -DCONFIG_AS_CFI=1 -DCONFIG_AS_CFI_SIGNAL_FRAME=1 -DCONFIG_AS_CFI_SECTIONS=1 -DCONFIG_AS_FXSAVEQ=1 -DCONFIG_AS_SSSE3=1 -DCONFIG_AS_CRC32=1 -DCONFIG_AS_AVX=1 -DCONFIG_AS_AVX2=1 -DCONFIG_AS_SHA1_NI=1 -DCONFIG_AS_SHA256_NI=1 -pipe -Wno-sign-compare -fno-asynchronous-unwind-tables -fno-delete-null-pointer-checks -Wno-maybe-uninitialized -O2 --param=allow-store-data-races=0 -Wframe-larger-than=2048 -fstack-protector-strong -Wno-unused-but-set-variable -fno-omit-frame-pointer -fno-optimize-sibling-calls -fno-var-tracking-assignments -g -pg -mfentry -DCC_USING_FENTRY -fno-inline-functions-called-once -Wdeclaration-after-statement -Wno-pointer-sign -fno-strict-overflow -fconserve-stack -Werror=implicit-int -Werror=strict-prototypes -DCC_HAVE_ASM_GOTO -D"KBUILD_STR(s)=#s" -D"KBUILD_BASENAME=KBUILD_STR(kerNotification.mod)" -D"KBUILD_MODNAME=KBUILD_STR(kerNotification)" -DMODULE -c -o /home/cmmdocker/kernel_prog/kerNotification.mod.o /home/cmmdocker/kernel_prog/kerNotification.mod.c
ld -r -m elf_x86_64 -T ./scripts/module-common.lds --build-id -o /home/cmmdocker/kernel_prog/kerNotification.ko /home/cmmdocker/kernel_prog/kerNotification.o /home/cmmdocker/kernel_prog/kerNotification.mod.o
make[1]: Leaving directory `/usr/src/kernels/4.4.57-1.el7.elrepo.x86_64'
Any idea how to fix this?

Answer 1

Issue was missing license. Below was added to get the expected result:
MODULE_LICENSE("GPL");
Referred the following answer from another query on stackoverflow for this: unknown-symbol-class-create-err-0

Answer 2

insmod: ERROR: could not insert module kerNotification.ko: Unknown
symbol in module
You get the above error because the net_namespace_list is missing in the kernel. So you need to make sure to insert the module which it is defined. looking at the source code its declared in net_namespace.c and looking at the Makefile it will when CONFIG_NET is enabled. Also when you have built your kernel image the System.map file should tell you if its declared in the kernel image which you have built, something like below:
cat System.map | grep net_namespace_list
8041a888 r __ksymtab_net_namespace_list
8042b80c r __kstrtab_net_namespace_list
80464c08 D net_namespace_list