coredump: move elf parsing utilities to src/shared/elf-util

3 files changed, 551 insertions, 0 deletions

diff --git a/src/shared/elf-util.c b/src/shared/elf-util.c
new file mode 100644
index 0000000000..12b42bf90f
--- /dev/null
+++ b/src/shared/elf-util.c
@@ -0,0 +1,535 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#include <dwarf.h>
+#include <elfutils/libdwelf.h>
+#include <elfutils/libdwfl.h>
+#include <libelf.h>
+#include <sys/prctl.h>
+#include <sys/resource.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include "alloc-util.h"
+#include "elf-util.h"
+#include "errno-util.h"
+#include "fileio.h"
+#include "fd-util.h"
+#include "format-util.h"
+#include "hexdecoct.h"
+#include "io-util.h"
+#include "macro.h"
+#include "process-util.h"
+#include "rlimit-util.h"
+#include "string-util.h"
+#include "util.h"
+
+#define FRAMES_MAX 64
+#define THREADS_MAX 64
+#define ELF_PACKAGE_METADATA_ID 0xcafe1a7e
+
+typedef struct StackContext {
+        FILE *f;
+        Dwfl *dwfl;
+        Elf *elf;
+        unsigned n_thread;
+        unsigned n_frame;
+        JsonVariant **package_metadata;
+        Set **modules;
+} StackContext;
+
+static StackContext* stack_context_destroy(StackContext *c) {
+        if (!c)
+                return NULL;
+
+        c->f = safe_fclose(c->f);
+
+        if (c->dwfl) {
+                dwfl_end(c->dwfl);
+                c->dwfl = NULL;
+        }
+
+        if (c->elf) {
+                elf_end(c->elf);
+                c->elf = NULL;
+        }
+
+        return NULL;
+}
+
+DEFINE_TRIVIAL_CLEANUP_FUNC_FULL(Elf *, elf_end, NULL);
+
+static int frame_callback(Dwfl_Frame *frame, void *userdata) {
+        StackContext *c = userdata;
+        Dwarf_Addr pc, pc_adjusted, bias = 0;
+        _cleanup_free_ Dwarf_Die *scopes = NULL;
+        const char *fname = NULL, *symbol = NULL;
+        Dwfl_Module *module;
+        bool is_activation;
+        uint64_t module_offset = 0;
+
+        assert(frame);
+        assert(c);
+
+        if (c->n_frame >= FRAMES_MAX)
+                return DWARF_CB_ABORT;
+
+        if (!dwfl_frame_pc(frame, &pc, &is_activation))
+                return DWARF_CB_ABORT;
+
+        pc_adjusted = pc - (is_activation ? 0 : 1);
+
+        module = dwfl_addrmodule(c->dwfl, pc_adjusted);
+        if (module) {
+                Dwarf_Die *s, *cudie;
+                int n;
+                Dwarf_Addr start;
+
+                cudie = dwfl_module_addrdie(module, pc_adjusted, &bias);
+                if (cudie) {
+                        n = dwarf_getscopes(cudie, pc_adjusted - bias, &scopes);
+                        if (n > 0)
+                                for (s = scopes; s && s < scopes + n; s++) {
+                                        if (IN_SET(dwarf_tag(s), DW_TAG_subprogram, DW_TAG_inlined_subroutine, DW_TAG_entry_point)) {
+                                                Dwarf_Attribute *a, space;
+
+                                                a = dwarf_attr_integrate(s, DW_AT_MIPS_linkage_name, &space);
+                                                if (!a)
+                                                        a = dwarf_attr_integrate(s, DW_AT_linkage_name, &space);
+                                                if (a)
+                                                        symbol = dwarf_formstring(a);
+                                                if (!symbol)
+                                                        symbol = dwarf_diename(s);
+
+                                                if (symbol)
+                                                        break;
+                                        }
+                                }
+                }
+
+                if (!symbol)
+                        symbol = dwfl_module_addrname(module, pc_adjusted);
+
+                fname = dwfl_module_info(module, NULL, &start, NULL, NULL, NULL, NULL, NULL);
+                module_offset = pc - start;
+        }
+
+        if (c->f)
+                fprintf(c->f, "#%-2u 0x%016" PRIx64 " %s (%s + 0x%" PRIx64 ")\n", c->n_frame, (uint64_t) pc, strna(symbol), strna(fname), module_offset);
+        c->n_frame++;
+
+        return DWARF_CB_OK;
+}
+
+static int thread_callback(Dwfl_Thread *thread, void *userdata) {
+        StackContext *c = userdata;
+        pid_t tid;
+
+        assert(thread);
+        assert(c);
+
+        if (c->n_thread >= THREADS_MAX)
+                return DWARF_CB_ABORT;
+
+        if (c->n_thread != 0 && c->f)
+                fputc('\n', c->f);
+
+        c->n_frame = 0;
+
+        if (c->f) {
+                tid = dwfl_thread_tid(thread);
+                fprintf(c->f, "Stack trace of thread " PID_FMT ":\n", tid);
+        }
+
+        if (dwfl_thread_getframes(thread, frame_callback, c) < 0)
+                return DWARF_CB_ABORT;
+
+        c->n_thread++;
+
+        return DWARF_CB_OK;
+}
+
+static int parse_package_metadata(const char *name, JsonVariant *id_json, Elf *elf, StackContext *c) {
+        size_t n_program_headers;
+        int r;
+
+        assert(name);
+        assert(elf);
+        assert(c);
+
+        /* When iterating over PT_LOAD we will visit modules more than once */
+        if (set_contains(*c->modules, name))
+                return 0;
+
+        r = elf_getphdrnum(elf, &n_program_headers);
+        if (r < 0) /* Not the handle we are looking for - that's ok, skip it */
+                return 0;
+
+        /* Iterate over all program headers in that ELF object. These will have been copied by
+         * the kernel verbatim when the core file is generated. */
+        for (size_t i = 0; i < n_program_headers; ++i) {
+                size_t note_offset = 0, name_offset, desc_offset;
+                GElf_Phdr mem, *program_header;
+                GElf_Nhdr note_header;
+                Elf_Data *data;
+
+                /* Package metadata is in PT_NOTE headers. */
+                program_header = gelf_getphdr(elf, i, &mem);
+                if (!program_header || program_header->p_type != PT_NOTE)
+                        continue;
+
+                /* Fortunately there is an iterator we can use to walk over the
+                 * elements of a PT_NOTE program header. We are interested in the
+                 * note with type. */
+                data = elf_getdata_rawchunk(elf,
+                                            program_header->p_offset,
+                                            program_header->p_filesz,
+                                            ELF_T_NHDR);
+                if (!data)
+                        continue;
+
+                while (note_offset < data->d_size &&
+                       (note_offset = gelf_getnote(data, note_offset, &note_header, &name_offset, &desc_offset)) > 0) {
+                        const char *note_name = (const char *)data->d_buf + name_offset;
+                        const char *payload = (const char *)data->d_buf + desc_offset;
+
+                        if (note_header.n_namesz == 0 || note_header.n_descsz == 0)
+                                continue;
+
+                        /* Package metadata might have different owners, but the
+                         * magic ID is always the same. */
+                        if (note_header.n_type == ELF_PACKAGE_METADATA_ID) {
+                                _cleanup_(json_variant_unrefp) JsonVariant *v = NULL, *w = NULL;
+
+                                r = json_parse(payload, 0, &v, NULL, NULL);
+                                if (r < 0)
+                                        return log_error_errno(r, "json_parse on %s failed: %m", payload);
+
+                                /* First pretty-print to the buffer, so that the metadata goes as
+                                 * plaintext in the journal. */
+                                if (c->f) {
+                                        fprintf(c->f, "Metadata for module %s owned by %s found: ",
+                                                name, note_name);
+                                        json_variant_dump(v, JSON_FORMAT_NEWLINE|JSON_FORMAT_PRETTY, c->f, NULL);
+                                        fputc('\n', c->f);
+                                }
+
+                                /* Secondly, if we have a build-id, merge it in the same JSON object
+                                 * so that it appears all nicely together in the logs/metadata. */
+                                if (id_json) {
+                                        r = json_variant_merge(&v, id_json);
+                                        if (r < 0)
+                                                return log_error_errno(r, "json_variant_merge of package meta with buildid failed: %m");
+                                }
+
+                                /* Then we build a new object using the module name as the key, and merge it
+                                 * with the previous parses, so that in the end it all fits together in a single
+                                 * JSON blob. */
+                                r = json_build(&w, JSON_BUILD_OBJECT(JSON_BUILD_PAIR(name, JSON_BUILD_VARIANT(v))));
+                                if (r < 0)
+                                        return log_error_errno(r, "Failed to build JSON object: %m");
+                                r = json_variant_merge(c->package_metadata, w);
+                                if (r < 0)
+                                        return log_error_errno(r, "json_variant_merge of package meta with buildid failed: %m");
+
+                                /* Finally stash the name, so we avoid double visits. */
+                                r = set_put_strdup(c->modules, name);
+                                if (r < 0)
+                                        return log_error_errno(r, "set_put_strdup failed: %m");
+
+                                return 1;
+                        }
+                }
+        }
+
+        /* Didn't find package metadata for this module - that's ok, just go to the next. */
+        return 0;
+}
+
+static int module_callback(Dwfl_Module *mod, void **userdata, const char *name, Dwarf_Addr start, void *arg) {
+        _cleanup_(json_variant_unrefp) JsonVariant *id_json = NULL;
+        StackContext *c = arg;
+        size_t n_program_headers;
+        GElf_Addr id_vaddr, bias;
+        const unsigned char *id;
+        int id_len, r;
+        Elf *elf;
+
+        assert(mod);
+        assert(c);
+
+        if (!name)
+                name = "(unnamed)"; /* For logging purposes */
+
+        /* We are iterating on each "module", which is what dwfl calls ELF objects contained in the
+         * core file, and extracting the build-id first and then the package metadata.
+         * We proceed in a best-effort fashion - not all ELF objects might contain both or either.
+         * The build-id is easy, as libdwfl parses it during the dwfl_core_file_report() call and
+         * stores it separately in an internal library struct. */
+        id_len = dwfl_module_build_id(mod, &id, &id_vaddr);
+        if (id_len <= 0) {
+                /* If we don't find a build-id, note it in the journal message, and try
+                 * anyway to find the package metadata. It's unlikely to have the latter
+                 * without the former, but there's no hard rule. */
+                if (c->f)
+                        fprintf(c->f, "Found module %s without build-id.\n", name);
+        } else {
+                JsonVariant *build_id;
+
+                /* We will later parse package metadata json and pass it to our caller. Prepare the
+                * build-id in json format too, so that it can be appended and parsed cleanly. It
+                * will then be added as metadata to the journal message with the stack trace. */
+                r = json_build(&id_json, JSON_BUILD_OBJECT(JSON_BUILD_PAIR("buildId", JSON_BUILD_HEX(id, id_len))));
+                if (r < 0) {
+                        log_error_errno(r, "json_build on build-id failed: %m");
+                        return DWARF_CB_ABORT;
+                }
+
+                build_id = json_variant_by_key(id_json, "buildId");
+                assert_se(build_id);
+                if (c->f)
+                        fprintf(c->f, "Found module %s with build-id: %s\n", name, json_variant_string(build_id));
+        }
+
+        /* The .note.package metadata is more difficult. From the module, we need to get a reference
+         * to the ELF object first. We might be lucky and just get it from elfutils. */
+        elf = dwfl_module_getelf(mod, &bias);
+        if (elf) {
+                r = parse_package_metadata(name, id_json, elf, c);
+                if (r < 0)
+                        return DWARF_CB_ABORT;
+                if (r > 0)
+                        return DWARF_CB_OK;
+        } else
+                elf = c->elf;
+
+        /* We did not get the ELF object, or it's just a reference to the core. That is likely
+         * because we didn't get direct access to the executable, and the version of elfutils does
+         * not yet support parsing it out of the core file directly.
+         * So fallback to manual extraction - get the PT_LOAD section from the core,
+         * and if it's the right one we can interpret it as an Elf object, and parse
+         * its notes manually. */
+
+        r = elf_getphdrnum(elf, &n_program_headers);
+        if (r < 0) {
+                log_warning("Could not parse number of program headers from core file: %s",
+                            elf_errmsg(-1)); /* -1 retrieves the most recent error */
+                return DWARF_CB_OK;
+        }
+
+        for (size_t i = 0; i < n_program_headers; ++i) {
+                GElf_Phdr mem, *program_header;
+                Elf_Data *data;
+
+                /* The core file stores the ELF files in the PT_LOAD segment. */
+                program_header = gelf_getphdr(elf, i, &mem);
+                if (!program_header || program_header->p_type != PT_LOAD)
+                        continue;
+
+                /* Now get a usable Elf reference, and parse the notes from it. */
+                data = elf_getdata_rawchunk(elf,
+                                            program_header->p_offset,
+                                            program_header->p_filesz,
+                                            ELF_T_NHDR);
+                if (!data)
+                        continue;
+
+                _cleanup_(elf_endp) Elf *memelf = elf_memory(data->d_buf, data->d_size);
+                if (!memelf)
+                        continue;
+                r = parse_package_metadata(name, id_json, memelf, c);
+                if (r < 0)
+                        return DWARF_CB_ABORT;
+                if (r > 0)
+                        break;
+        }
+
+        return DWARF_CB_OK;
+}
+
+static int parse_core(int fd, const char *executable, char **ret, JsonVariant **ret_package_metadata) {
+
+        static const Dwfl_Callbacks callbacks = {
+                .find_elf = dwfl_build_id_find_elf,
+                .section_address = dwfl_offline_section_address,
+                .find_debuginfo = dwfl_standard_find_debuginfo,
+        };
+
+        _cleanup_(json_variant_unrefp) JsonVariant *package_metadata = NULL;
+        _cleanup_(set_freep) Set *modules = NULL;
+        _cleanup_free_ char *buf = NULL; /* buf should be freed last, c.f closed first (via stack_context_destroy) */
+        _cleanup_(stack_context_destroy) StackContext c = {
+                .package_metadata = &package_metadata,
+                .modules = &modules,
+        };
+        size_t sz = 0;
+        int r;
+
+        assert(fd >= 0);
+
+        if (lseek(fd, 0, SEEK_SET) == (off_t) -1)
+                return log_warning_errno(errno, "Failed to seek to beginning of the core file: %m");
+
+        if (ret) {
+                c.f = open_memstream_unlocked(&buf, &sz);
+                if (!c.f)
+                        return log_oom();
+        }
+
+        elf_version(EV_CURRENT);
+
+        c.elf = elf_begin(fd, ELF_C_READ_MMAP, NULL);
+        if (!c.elf)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, elf_begin() failed: %s", elf_errmsg(elf_errno()));
+
+        c.dwfl = dwfl_begin(&callbacks);
+        if (!c.dwfl)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_begin() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (dwfl_core_file_report(c.dwfl, c.elf, executable) < 0)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_core_file_report() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (dwfl_report_end(c.dwfl, NULL, NULL) != 0)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_report_end() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (dwfl_getmodules(c.dwfl, &module_callback, &c, 0) < 0)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_getmodules() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (dwfl_core_file_attach(c.dwfl, c.elf) < 0)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_core_file_attach() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (dwfl_getthreads(c.dwfl, thread_callback, &c) < 0)
+                return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Could not parse core file, dwfl_getthreads() failed: %s", dwfl_errmsg(dwfl_errno()));
+
+        if (ret) {
+                r = fflush_and_check(c.f);
+                if (r < 0)
+                        return log_warning_errno(r, "Could not parse core file, flushing file buffer failed: %m");
+
+                c.f = safe_fclose(c.f);
+                *ret = TAKE_PTR(buf);
+        }
+        if (ret_package_metadata)
+                *ret_package_metadata = TAKE_PTR(package_metadata);
+
+        return 0;
+}
+
+int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, char **ret, JsonVariant **ret_package_metadata) {
+        _cleanup_close_pair_ int error_pipe[2] = { -1, -1 }, return_pipe[2] = { -1, -1 }, json_pipe[2] = { -1, -1 };
+        _cleanup_(json_variant_unrefp) JsonVariant *package_metadata = NULL;
+        _cleanup_free_ char *buf = NULL;
+        int r;
+
+        r = RET_NERRNO(pipe2(error_pipe, O_CLOEXEC|O_NONBLOCK));
+        if (r < 0)
+                return r;
+
+        if (ret) {
+                r = RET_NERRNO(pipe2(return_pipe, O_CLOEXEC));
+                if (r < 0)
+                        return r;
+        }
+
+        if (ret_package_metadata) {
+                r = RET_NERRNO(pipe2(json_pipe, O_CLOEXEC));
+                if (r < 0)
+                        return r;
+        }
+
+        /* Parsing possibly malformed data is crash-happy, so fork. In case we crash,
+         * the core file will not be lost, and the messages will still be attached to
+         * the journal. Reading the elf object might be slow, but it still has an upper
+         * bound since the core files have an upper size limit. It's also not doing any
+         * system call or interacting with the system in any way, besides reading from
+         * the file descriptor and writing into these four pipes. */
+        r = safe_fork_full("(sd-parse-elf)",
+                           (int[]){ fd, error_pipe[1], return_pipe[1], json_pipe[1] },
+                           4,
+                           FORK_RESET_SIGNALS|FORK_CLOSE_ALL_FDS|FORK_NEW_MOUNTNS|FORK_MOUNTNS_SLAVE|FORK_NEW_USERNS|FORK_WAIT|FORK_REOPEN_LOG,
+                           NULL);
+        if (r < 0) {
+                if (r == -EPROTO) { /* We should have the errno from the child, but don't clobber original error */
+                        int e, k;
+
+                        k = read(error_pipe[0], &e, sizeof(e));
+                        if (k < 0 && errno != EAGAIN) /* Pipe is non-blocking, EAGAIN means there's nothing */
+                                return -errno;
+                        if (k == sizeof(e))
+                                return e; /* propagate error sent to us from child */
+                        if (k != 0)
+                                return -EIO;
+                }
+
+                return r;
+        }
+        if (r == 0) {
+                /* We want to avoid loops, given this can be called from systemd-coredump */
+                if (fork_disable_dump)
+                        prctl(PR_SET_DUMPABLE, 0);
+
+                r = parse_core(fd, executable, ret ? &buf : NULL, ret_package_metadata ? &package_metadata : NULL);
+                if (r < 0)
+                        goto child_fail;
+
+                if (buf) {
+                        r = loop_write(return_pipe[1], buf, strlen(buf), false);
+                        if (r < 0)
+                                goto child_fail;
+
+                        return_pipe[1] = safe_close(return_pipe[1]);
+                }
+
+                if (package_metadata) {
+                        _cleanup_fclose_ FILE *json_out = NULL;
+
+                        json_out = take_fdopen(&json_pipe[1], "w");
+                        if (!json_out) {
+                                r = -errno;
+                                goto child_fail;
+                        }
+
+                        json_variant_dump(package_metadata, JSON_FORMAT_FLUSH, json_out, NULL);
+                }
+
+                _exit(EXIT_SUCCESS);
+
+        child_fail:
+                (void) write(error_pipe[1], &r, sizeof(r));
+                _exit(EXIT_FAILURE);
+        }
+
+        error_pipe[1] = safe_close(error_pipe[1]);
+        return_pipe[1] = safe_close(return_pipe[1]);
+        json_pipe[1] = safe_close(json_pipe[1]);
+
+        if (ret) {
+                _cleanup_fclose_ FILE *in = NULL;
+
+                in = take_fdopen(&return_pipe[0], "r");
+                if (!in)
+                        return -errno;
+
+                r = read_full_stream(in, &buf, NULL);
+                if (r < 0)
+                        return r;
+        }
+
+        if (ret_package_metadata) {
+                _cleanup_fclose_ FILE *json_in = NULL;
+
+                json_in = take_fdopen(&json_pipe[0], "r");
+                if (!json_in)
+                        return -errno;
+
+                r = json_parse_file(json_in, NULL, 0, &package_metadata, NULL, NULL);
+                if (r < 0 && r != -EINVAL) /* EINVAL: json was empty, so we got nothing, but that's ok */
+                        return r;
+        }
+
+        if (ret)
+                *ret = TAKE_PTR(buf);
+        if (ret_package_metadata)
+                *ret_package_metadata = TAKE_PTR(package_metadata);
+
+        return 0;
+}
diff --git a/src/shared/elf-util.h b/src/shared/elf-util.h
new file mode 100644
index 0000000000..429fb5c912
--- /dev/null
+++ b/src/shared/elf-util.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+#pragma once
+
+#include "json.h"
+
+/* Parse an ELF object in a forked process, so that errors while iterating over
+ * untrusted and potentially malicious data do not propagate to the main caller's process.
+ * If fork_disable_dump, the child process will not dump core if it crashes. */
+int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, char **ret, JsonVariant **ret_package_metadata);
diff --git a/src/shared/meson.build b/src/shared/meson.build
index 130c03ec99..2187cc6205 100644
--- a/src/shared/meson.build
+++ b/src/shared/meson.build
@@ -388,6 +388,12 @@ if conf.get('ENABLE_NSCD') == 1
         shared_sources += files('nscd-flush.c')
 endif
 
+if conf.get('HAVE_ELFUTILS') == 1
+        shared_sources += files(
+                'elf-util.c',
+                'elf-util.h')
+endif
+
 generate_ip_protocol_list = find_program('generate-ip-protocol-list.sh')
 ip_protocol_list_txt = custom_target(
         'ip-protocol-list.txt',
@@ -436,6 +442,7 @@ libshared_deps = [threads,
                   libcap,
                   libcrypt,
                   libdl,
+                  libdw,
                   libgcrypt,
                   libiptc,
                   libkmod,