Previously, dependency chain of JoinsNamespaceOf= did not work, e.g.
- a.service has JoinsNamespaceOf=b.service
- b.service has JoinsNamespaceOf=c.service
if, first c.service, next a.service, finally b.service is started,
then a.service is not joined to the namespace of c.service. And, as
mentioned in the document, the namespace used by b.service is not
deterministic.
This makes when searching exsiting namespace to be joined, all units in
the transitive dependency of JoinsNamespaceOf= are checked.
Previously, even if a.service has JoinsNamespaceOf=b.service, the
inverse direction of reference was not introduced.
Hence, a.service is started earlier than b.service, the namespace will
not shared with b.service.
Also, even if a.service had the reference to b.service, b.service did not.
If b.service is freed earlier, then unit_clear_dependencies() does not clear
the reference from a to b, and will cause use-after-free on unit_free() for
a.service.
Let's make JoinsNamespaceOf=b.service in a.service implies the inverse
dependency, i.e. JoinsNamespaceOf=a.service for b.service. Then, we can safely
free b.service.
We can't dereference the variant object directly, as it might be
a magic object (which has an address on a faulting page); use
json_variant_is_sensitive() instead that handles this case.
For example, with an empty array:
==1547789==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000023 (pc 0x7fd616ca9a18 bp 0x7ffcba1dc7c0 sp 0x7ffcba1dc6d0 T0)
==1547789==The signal is caused by a READ memory access.
==1547789==Hint: address points to the zero page.
SCARINESS: 10 (null-deref)
#0 0x7fd616ca9a18 in json_variant_strv ../src/shared/json.c:2190
#1 0x408332 in oci_args ../src/nspawn/nspawn-oci.c:173
#2 0x7fd616cc09ce in json_dispatch ../src/shared/json.c:4400
#3 0x40addf in oci_process ../src/nspawn/nspawn-oci.c:428
#4 0x7fd616cc09ce in json_dispatch ../src/shared/json.c:4400
#5 0x41fef5 in oci_load ../src/nspawn/nspawn-oci.c:2187
#6 0x4061e4 in LLVMFuzzerTestOneInput ../src/nspawn/fuzz-nspawn-oci.c:23
#7 0x40691c in main ../src/fuzz/fuzz-main.c:50
#8 0x7fd61564a50f in __libc_start_call_main (/lib64/libc.so.6+0x2750f)
#9 0x7fd61564a5c8 in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x275c8)
#10 0x405da4 in _start (/home/fsumsal/repos/@systemd/systemd/build-san/fuzz-nspawn-oci+0x405da4)
DEDUP_TOKEN: json_variant_strv--oci_args--json_dispatch
AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV ../src/shared/json.c:2190 in json_variant_strv
==1547789==ABORTING
Or with an empty string in an array:
../src/shared/json.c:2202:39: runtime error: member access within misaligned address 0x000000000007 for type 'struct JsonVariant', which requires 8 byte alignment
0x000000000007: note: pointer points here
<memory cannot be printed>
#0 0x7f35f4ca9bcf in json_variant_strv ../src/shared/json.c:2202
#1 0x408332 in oci_args ../src/nspawn/nspawn-oci.c:173
#2 0x7f35f4cc09ce in json_dispatch ../src/shared/json.c:4400
#3 0x40addf in oci_process ../src/nspawn/nspawn-oci.c:428
#4 0x7f35f4cc09ce in json_dispatch ../src/shared/json.c:4400
#5 0x41fef5 in oci_load ../src/nspawn/nspawn-oci.c:2187
#6 0x4061e4 in LLVMFuzzerTestOneInput ../src/nspawn/fuzz-nspawn-oci.c:23
#7 0x40691c in main ../src/fuzz/fuzz-main.c:50
#8 0x7f35f364a50f in __libc_start_call_main (/lib64/libc.so.6+0x2750f)
#9 0x7f35f364a5c8 in __libc_start_main@GLIBC_2.2.5 (/lib64/libc.so.6+0x275c8)
#10 0x405da4 in _start (/home/fsumsal/repos/@systemd/systemd/build-san/fuzz-nspawn-oci+0x405da4)
SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior ../src/shared/json.c:2202:39 in
Note: this happens only if json_variant_copy() in json_variant_set_source() fails.
Found by Nallocfuzz.
