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Fix coredump deadlock with overly long backtraces #25055

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merged 3 commits into from
Oct 19, 2022
Merged

Fix coredump deadlock with overly long backtraces #25055

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7922ead
shared/json: allow json_variant_dump() to return an error
keszybz Oct 18, 2022
87a16eb
shared/json: use different return code for empty input
keszybz Oct 19, 2022
076b807
coredump: avoid deadlock when passing processed backtrace data
keszybz Oct 18, 2022
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39 changes: 32 additions & 7 deletions src/shared/elf-util.c
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,9 @@
#define THREADS_MAX 64
#define ELF_PACKAGE_METADATA_ID 0xcafe1a7e

/* The amount of data we're willing to write to each of the output pipes. */
#define COREDUMP_PIPE_MAX (1024*1024U)

static void *dw_dl = NULL;
static void *elf_dl = NULL;

Expand Down Expand Up @@ -759,13 +762,13 @@ int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, cha
return r;

if (ret) {
r = RET_NERRNO(pipe2(return_pipe, O_CLOEXEC));
r = RET_NERRNO(pipe2(return_pipe, O_CLOEXEC|O_NONBLOCK));
if (r < 0)
return r;
}

if (ret_package_metadata) {
r = RET_NERRNO(pipe2(json_pipe, O_CLOEXEC));
r = RET_NERRNO(pipe2(json_pipe, O_CLOEXEC|O_NONBLOCK));
if (r < 0)
return r;
}
Expand Down Expand Up @@ -809,8 +812,24 @@ int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, cha
goto child_fail;

if (buf) {
r = loop_write(return_pipe[1], buf, strlen(buf), false);
if (r < 0)
size_t len = strlen(buf);

if (len > COREDUMP_PIPE_MAX) {
/* This is iffy. A backtrace can be a few hundred kilobytes, but too much is
* too much. Let's log a warning and ignore the rest. */
log_warning("Generated backtrace is %zu bytes (more than the limit of %u bytes), backtrace will be truncated.",
len, COREDUMP_PIPE_MAX);
len = COREDUMP_PIPE_MAX;
}

/* Bump the space for the returned string.
* Failure is ignored, because partial output is still useful. */
(void) fcntl(return_pipe[1], F_SETPIPE_SZ, len);

r = loop_write(return_pipe[1], buf, len, false);
if (r == -EAGAIN)
log_warning("Write failed, backtrace will be truncated.");
else if (r < 0)
goto child_fail;

return_pipe[1] = safe_close(return_pipe[1]);
Expand All @@ -819,13 +838,19 @@ int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, cha
if (package_metadata) {
_cleanup_fclose_ FILE *json_out = NULL;

/* Bump the space for the returned string. We don't know how much space we'll need in
* advance, so we'll just try to write as much as possible and maybe fail later. */
(void) fcntl(json_pipe[1], F_SETPIPE_SZ, COREDUMP_PIPE_MAX);

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);
r = json_variant_dump(package_metadata, JSON_FORMAT_FLUSH, json_out, NULL);
if (r < 0)
log_warning_errno(r, "Failed to write JSON package metadata, ignoring: %m");
}

_exit(EXIT_SUCCESS);
Expand Down Expand Up @@ -859,8 +884,8 @@ int parse_elf_object(int fd, const char *executable, bool fork_disable_dump, cha
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 (r < 0 && r != -ENODATA) /* ENODATA: json was empty, so we got nothing, but that's ok */
log_warning_errno(r, "Failed to read or parse json metadata, ignoring: %m");
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}

if (ret)
Expand Down
13 changes: 8 additions & 5 deletions src/shared/json.c
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Expand Up @@ -1785,9 +1785,9 @@ int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret) {
return (int) sz - 1;
}

void json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const char *prefix) {
int json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const char *prefix) {
if (!v)
return;
return 0;

if (!f)
f = stdout;
Expand All @@ -1813,7 +1813,8 @@ void json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const cha
fputc('\n', f); /* In case of SSE add a second newline */

if (flags & JSON_FORMAT_FLUSH)
fflush(f);
return fflush_and_check(f);
return 0;
}

int json_variant_filter(JsonVariant **v, char **to_remove) {
Expand Down Expand Up @@ -3186,7 +3187,6 @@ int json_parse_continue(const char **p, JsonParseFlags flags, JsonVariant **ret,
int json_parse_file_at(FILE *f, int dir_fd, const char *path, JsonParseFlags flags, JsonVariant **ret, unsigned *ret_line, unsigned *ret_column) {
_cleanup_(json_source_unrefp) JsonSource *source = NULL;
_cleanup_free_ char *text = NULL;
const char *p;
int r;

if (f)
Expand All @@ -3198,13 +3198,16 @@ int json_parse_file_at(FILE *f, int dir_fd, const char *path, JsonParseFlags fla
if (r < 0)
return r;

if (isempty(text))
return -ENODATA;

if (path) {
source = json_source_new(path);
if (!source)
return -ENOMEM;
}

p = text;
const char *p = text;
return json_parse_internal(&p, source, flags, ret, ret_line, ret_column, false);
}

Expand Down
2 changes: 1 addition & 1 deletion src/shared/json.h
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Original file line number Diff line number Diff line change
Expand Up @@ -197,7 +197,7 @@ typedef enum JsonFormatFlags {
} JsonFormatFlags;

int json_variant_format(JsonVariant *v, JsonFormatFlags flags, char **ret);
void json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const char *prefix);
int json_variant_dump(JsonVariant *v, JsonFormatFlags flags, FILE *f, const char *prefix);

int json_variant_filter(JsonVariant **v, char **to_remove);

Expand Down
18 changes: 18 additions & 0 deletions src/test/test-json.c
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Expand Up @@ -344,6 +344,24 @@ TEST(build) {
assert_se(json_variant_equal(a, b));
}

TEST(json_parse_file_empty) {
_cleanup_fclose_ FILE *f = NULL;
_cleanup_(json_variant_unrefp) JsonVariant *v = NULL;

assert_se(fopen_unlocked("/dev/null", "re", &f) >= 0);
assert_se(json_parse_file(f, "waldo", 0, &v, NULL, NULL) == -ENODATA);
assert_se(v == NULL);
}

TEST(json_parse_file_invalid) {
_cleanup_fclose_ FILE *f = NULL;
_cleanup_(json_variant_unrefp) JsonVariant *v = NULL;

assert_se(f = fmemopen_unlocked((void*) "kookoo", 6, "r"));
assert_se(json_parse_file(f, "waldo", 0, &v, NULL, NULL) == -EINVAL);
assert_se(v == NULL);
}

TEST(source) {
static const char data[] =
"\n"
Expand Down