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serialize: don#t allocate 1M on the stack just like that

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Prompted by: https://github.com/systemd/systemd/pull/27890#issuecomment-1712841117
This commit is contained in:
Lennart Poettering 2023-09-11 12:21:14 +02:00 committed by Luca Boccassi
parent e4aab5cf1a
commit f96a32c7f0
1 changed files with 27 additions and 9 deletions
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36
src/shared/serialize.c
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@ -24,10 +24,8 @@ int serialize_item(FILE *f, const char *key, const char *value) {
/* Make sure that anything we serialize we can also read back again with read_line() with a maximum line size
* of LONG_LINE_MAX. This is a safety net only. All code calling us should filter this out earlier anyway. */
if (strlen(key) + 1 + strlen(value) + 1 > LONG_LINE_MAX) {
log_warning("Attempted to serialize overly long item '%s', refusing.", key);
return -EINVAL;
}
if (strlen(key) + 1 + strlen(value) + 1 > LONG_LINE_MAX)
return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Attempted to serialize overly long item '%s', refusing.", key);
fputs(key, f);
fputc('=', f);
@ -54,7 +52,10 @@ int serialize_item_escaped(FILE *f, const char *key, const char *value) {
}
int serialize_item_format(FILE *f, const char *key, const char *format, ...) {
char buf[LONG_LINE_MAX];
_cleanup_free_ char *allocated = NULL;
char buf[256]; /* Something resonably short that fits nicely on any stack (i.e. is considerably less
* than LONG_LINE_MAX (1MiB!) */
const char *b;
va_list ap;
int k;
@ -62,18 +63,35 @@ int serialize_item_format(FILE *f, const char *key, const char *format, ...) {
assert(key);
assert(format);
/* First, let's try to format this into a stack buffer */
va_start(ap, format);
k = vsnprintf(buf, sizeof(buf), format, ap);
va_end(ap);
if (k < 0 || (size_t) k >= sizeof(buf) || strlen(key) + 1 + k + 1 > LONG_LINE_MAX) {
log_warning("Attempted to serialize overly long item '%s', refusing.", key);
return -EINVAL;
if (k < 0)
return log_warning_errno(errno, "Failed to serialize item '%s', ignoring: %m", key);
if (strlen(key) + 1 + k + 1 > LONG_LINE_MAX) /* See above */
return log_warning_errno(SYNTHETIC_ERRNO(EINVAL), "Attempted to serialize overly long item '%s', refusing.", key);
if ((size_t) k < sizeof(buf))
b = buf; /* Yay, it fit! */
else {
/* So the string didn't fit in the short buffer above, but was not above our total limit,
* hence let's format it via dynamic memory */
va_start(ap, format);
k = vasprintf(&allocated, format, ap);
va_end(ap);
if (k < 0)
return log_warning_errno(errno, "Failed to serialize item '%s', ignoring: %m", key);
b = allocated;
}
fputs(key, f);
fputc('=', f);
fputs(buf, f);
fputs(b, f);
fputc('\n', f);
return 1;