[2020-02] [reflection] Check whether a pointer is valid before dereferencing #19842
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`Xamarin.Android` native runtime calls `mono_reflection_type_from_name`
and passes `NULL` as the `image` parameter. The parameter is then
propagated all the way to `_mono_reflection_get_type_from_info` where,
in case the assembly isn't loaded yet, it is used to obtain base
directory of the assembly. However, since the `image` parameter is
`NULL` in our case, attempt to dereference it causes a segfault:
libc : Fatal signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x4c0 in tid 11029 (ompanyname.app3), pid 11029 (ompanyname.app3)
crash_dump64: obtaining output fd from tombstoned, type: kDebuggerdTombstone
/system/bin/tombstoned: received crash request for pid 11029
crash_dump64: performing dump of process 11029 (target tid = 11029)
DEBUG : *** *** *** *** *** *** *** *** *** *** *** *** *** *** *** ***
DEBUG : Build fingerprint: 'google/sdk_gphone_x86_64/generic_x86_64:10/QSR1.190920.001/5891938:user/release-keys'
DEBUG : Revision: '0'
DEBUG : ABI: 'x86_64'
DEBUG : Timestamp: 2020-05-25 14:45:29+0200
DEBUG : pid: 11029, tid: 11029, name: ompanyname.app3 >>> com.companyname.app3 <<<
DEBUG : uid: 10134
DEBUG : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0x4c0
DEBUG : Cause: null pointer dereference
DEBUG : rax 000000000000002f rbx 0000000000000001 rcx 0000000000000000 rdx 0000000000000030
DEBUG : r8 0000000000000003 r9 000000000013e2e2 r10 0173eed800000000 r11 0000000000000206
DEBUG : r12 0000000000000000 r13 00007478530343c0 r14 00007478075eda33 r15 000074780763efb0
DEBUG : rdi 0000000000000000 rsi 00007478e2cb14d0
DEBUG : rbp 00007ffef3a35680 rsp 00007ffef3a355d0 rip 0000747807a4066a
DEBUG :
DEBUG : backtrace:
DEBUG : #00 pc 00000000003ba66a /data/app/com.companyname.app3-aQUF6Ge6_v-WaLb5i8Q7vw==/lib/x86_64/libmonosgen-2.0.so (_mono_reflection_get_type_from_info+474)
DEBUG : mono#1 pc 00000000003ba3d1 /data/app/com.companyname.app3-aQUF6Ge6_v-WaLb5i8Q7vw==/lib/x86_64/libmonosgen-2.0.so (mono_reflection_type_from_name_checked+321)
DEBUG : mono#2 pc 00000000003ba26d /data/app/com.companyname.app3-aQUF6Ge6_v-WaLb5i8Q7vw==/lib/x86_64/libmonosgen-2.0.so (mono_reflection_type_from_name+125)
DEBUG : mono#3 pc 000000000000ddb5 /data/app/com.companyname.app3-aQUF6Ge6_v-WaLb5i8Q7vw==/lib/x86_64/libmonodroid.so (xamarin::android::internal::EmbeddedAssemblies::typemap_java_to_managed(char const*)+389) (BuildId: 9952f1cfe0d910ae631abc73479f88eef34fd71d)
DEBUG : mono#4 pc 000000000000def3 /data/app/com.companyname.app3-aQUF6Ge6_v-WaLb5i8Q7vw==/lib/x86_64/libmonodroid.so (xamarin::android::internal::EmbeddedAssemblies::typemap_java_to_managed(_MonoString*)+99) (BuildId: 9952f1cfe0d910ae631abc73479f88eef34fd71d)
DEBUG : mono#5 pc 0000000000069532 <anonymous:5ad25000>
Even though this happens in `Xamarin.Android`, the error may occur for
any embedding application which passes `NULL` for the `image` parameter
in situation when the assembly isn't in memory yet.
CoffeeFlux
approved these changes
May 25, 2020
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Xamarin.Androidnative runtime callsmono_reflection_type_from_nameand passes
NULLas theimageparameter. The parameter is thenpropagated all the way to
_mono_reflection_get_type_from_infowhere,in case the assembly isn't loaded yet, it is used to obtain base
directory of the assembly. However, since the
imageparameter isNULLin our case, attempt to dereference it causes a segfault:Even though this happens in
Xamarin.Android, the error may occur forany embedding application which passes
NULLfor theimageparameterin situation when the assembly isn't in memory yet.
Backport of #19839.
/cc @CoffeeFlux @grendello