[Bug shlibs/30663] New: Segfault when reading malformed PT_INTERP header

["mattlloydhouse at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=30663

            Bug ID: 30663
           Summary: Segfault when reading malformed PT_INTERP header
           Product: gdb
           Version: HEAD
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: shlibs
          Assignee: unassigned at sourceware dot org
          Reporter: mattlloydhouse at gmail dot com
  Target Milestone: ---

Created attachment 14995
  --> https://sourceware.org/bugzilla/attachment.cgi?id=14995&action=edit
The program used for reproduction.

In find_program_interpreter() in gdb/solib-svr4.c, if there isn't a current
exec_bfd, then the interpreter string is read using
read_program_header(PT_INTERP), which reads phdr->p_memsz bytes starting at
phdr->p_vaddr in inferior memory. This may return an empty byte vector, or a
vector that is not null-terminated. (The Linux kernel's ELF loader only
verifies that the phdr->p_filesz bytes starting at phdr->p_offset in the file
are null-terminated.)

However, enable_break() in gdb/solib-svr4.c passes a pointer to the byte
vector's buffer to solib_bfd_open(), which passes it to solib_find(), which
calls xstrdup() to copy it. If the byte vector is empty (i.e., phdr->p_memsz ==
0), then its buffer is set to a null pointer, and this raises a segfault.
Presumably, other issues can occur if the vector otherwise isn't
null-terminated.

I can reproduce this on the latest snapshot by writing an ELF program with
ehdr->e_ident[EI_VERSION] == EV_NONE to prevent the file from being loaded by
GDB, and phdr->p_memsz == 0 on the PT_INTERP header to cause the segfault.
Then, I run it indirectly via env(1).

$ xxd -r <<EOF > program
00000000: 7f45 4c46 0201 0003 0000 0000 0000 0000  .ELF............
00000010: 0300 3e00 0100 0000 0000 0000 0000 0000  ..>.............
00000020: 4000 0000 0000 0000 0000 0000 0000 0000  @...............
00000030: 0000 0000 4000 3800 0200 4000 0000 0000  ....@.8...@.....
00000040: 0300 0000 0400 0000 b000 0000 0000 0000  ................
00000050: b000 0000 0000 0000 0000 0000 0000 0000  ................
00000060: 1c00 0000 0000 0000 0000 0000 0000 0000  ................
00000070: 0000 0000 0000 0000 0100 0000 0500 0000  ................
00000080: 0000 0000 0000 0000 0000 0000 0000 0000  ................
00000090: 0000 0000 0000 0000 cc00 0000 0000 0000  ................
000000a0: cc00 0000 0000 0000 0000 0000 0000 0000  ................
000000b0: 2f6c 6962 3634 2f6c 642d 6c69 6e75 782d  /lib64/ld-linux-
000000c0: 7838 362d 3634 2e73 6f2e 3200            x86-64.so.2.
EOF
$ chmod +x program
$ gdb --args env ./program 
GNU gdb (GDB) 14.0.50.20230721-git
Copyright (C) 2023 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
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There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<https://www.gnu.org/software/gdb/bugs/>.
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    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word"...
Reading symbols from env...
(No debugging symbols found in env)
(gdb) run
Starting program: /usr/bin/env ./program
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
process 1096118 is executing new program: /home/lm978/program
warning: "/home/lm978/program": not in executable format: file format not
recognized
warning: `/home/lm978/program': can't read symbols: file format not recognized.


Fatal signal: Segmentation fault
----- Backtrace -----
0x56522c29ff90 gdb_internal_backtrace_1
    /home/lm978/gdb-14.0.50.20230721/gdb/bt-utils.c:122
0x56522c29ff90 _Z22gdb_internal_backtracev
    /home/lm978/gdb-14.0.50.20230721/gdb/bt-utils.c:168
0x56522c3c695e handle_fatal_signal
    /home/lm978/gdb-14.0.50.20230721/gdb/event-top.c:889
0x56522c3c6b18 handle_sigsegv
    /home/lm978/gdb-14.0.50.20230721/gdb/event-top.c:962
0x7fd3cf2c451f ???
    ./signal/../sysdeps/unix/sysv/linux/x86_64/libc_sigaction.c:0
0x7fd3cf41f97d ???
    ../sysdeps/x86_64/multiarch/strlen-avx2.S:74
0x56522c7bc352 xstrdup
    ./xstrdup.c:33
0x56522c57ca8d solib_find_1
    /home/lm978/gdb-14.0.50.20230721/gdb/solib.c:184
0x56522c57d71a _Z10solib_findPKcPi
    /home/lm978/gdb-14.0.50.20230721/gdb/solib.c:419
0x56522c57d842 _Z14solib_bfd_openPKc
    /home/lm978/gdb-14.0.50.20230721/gdb/solib.c:456
0x56522c57873e enable_break
    /home/lm978/gdb-14.0.50.20230721/gdb/solib-svr4.c:2444
0x56522c57873e svr4_solib_create_inferior_hook
    /home/lm978/gdb-14.0.50.20230721/gdb/solib-svr4.c:3163
0x56522c461c8e _ZNKSt8functionIFvP8inferiorS1_EEclES1_S1_
    /usr/include/c++/11/bits/std_function.h:590
0x56522c461c8e _ZNK3gdb9observers10observableIJP8inferiorS3_EE6notifyES3_S3_
    ./../gdbsupport/observable.h:166
0x56522c461c8e follow_exec
    /home/lm978/gdb-14.0.50.20230721/gdb/infrun.c:1371
0x56522c461c8e handle_inferior_event
    /home/lm978/gdb-14.0.50.20230721/gdb/infrun.c:6051
0x56522c462aca _Z20fetch_inferior_eventv
    /home/lm978/gdb-14.0.50.20230721/gdb/infrun.c:4462
0x56522c7ce755 gdb_wait_for_event
    /home/lm978/gdb-14.0.50.20230721/gdbsupport/event-loop.cc:694
0x56522c7cf1e9 gdb_wait_for_event
    /home/lm978/gdb-14.0.50.20230721/gdbsupport/event-loop.cc:593
0x56522c7cf1e9 _Z16gdb_do_one_eventi
    /home/lm978/gdb-14.0.50.20230721/gdbsupport/event-loop.cc:217
0x56522c4ade89 start_event_loop
    /home/lm978/gdb-14.0.50.20230721/gdb/main.c:412
0x56522c4ade89 captured_command_loop
    /home/lm978/gdb-14.0.50.20230721/gdb/main.c:476
0x56522c4b0394 captured_main
    /home/lm978/gdb-14.0.50.20230721/gdb/main.c:1320
0x56522c4b0394 _Z8gdb_mainP18captured_main_args
    /home/lm978/gdb-14.0.50.20230721/gdb/main.c:1339
0x56522c1e6ccf main
    /home/lm978/gdb-14.0.50.20230721/gdb/gdb.c:32
---------------------
A fatal error internal to GDB has been detected, further
debugging is not possible.  GDB will now terminate.

This is a bug, please report it.  For instructions, see:
<https://www.gnu.org/software/gdb/bugs/>.

Segmentation fault (core dumped)

System info:

$ uname -a
Linux firmament 5.15.0-75-generic #82-Ubuntu SMP Tue Jun 6 23:10:23 UTC 2023
x86_64 x86_64 x86_64 GNU/Linux
$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11.3.0-1ubuntu1~22.04.1' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-aYxV0E/gcc-11-11.3.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-aYxV0E/gcc-11-11.3.0/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.3.0 (Ubuntu 11.3.0-1ubuntu1~22.04.1)

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