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criu/log: properly handle truncated length from vsnprintf

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vsnprintf does not always return the number of bytes actually written to
the buffer.

If the output was truncated due to the buffer limit, the return value is
the total number of bytes which WOULD have been written to the final
string if enough space had been available.

This means we must cap the return value to the buffer size excluding the
terminating null byte to correctly calculate the log entry size.

Signed-off-by: Andrei Vagin <avagin@google.com>
This commit is contained in:
Andrei Vagin 2025-11-11 15:21:09 -08:00 • committed by Andrei Vagin
parent 6344e8d71c
commit e689d902b3
1 changed files with 11 additions and 5 deletions
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16
criu/log.c
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@ -202,7 +202,7 @@ void flush_early_log_buffer(int fd)
}
pos += hdr->len;
}
if (early_log_buf_off == EARLY_LOG_BUF_LEN)
if ((early_log_buf_off + sizeof(struct early_log_hdr)) >= EARLY_LOG_BUF_LEN)
pr_warn("The early log buffer is full, some messages may have been lost\n");
early_log_buf_off = 0;
}
@ -320,7 +320,7 @@ unsigned int log_get_loglevel(void)
static void early_vprint(const char *format, unsigned int loglevel, va_list params)
{
unsigned int log_size = 0;
int log_size = 0, log_space;
struct early_log_hdr *hdr;
if ((early_log_buf_off + sizeof(hdr)) >= EARLY_LOG_BUF_LEN)
@ -332,6 +332,7 @@ static void early_vprint(const char *format, unsigned int loglevel, va_list para
hdr->level = loglevel;
/* Skip the log entry size */
early_log_buf_off += sizeof(hdr);
log_space = EARLY_LOG_BUF_LEN - early_log_buf_off;
if (loglevel >= LOG_TIMESTAMP) {
/*
* If logging is not yet setup we just write zeros
@ -339,12 +340,17 @@ static void early_vprint(const char *format, unsigned int loglevel, va_list para
* keep the same format as the other messages on
* log levels with timestamps (>=LOG_TIMESTAMP).
*/
log_size = snprintf(early_log_buffer + early_log_buf_off, sizeof(early_log_buffer) - early_log_buf_off,
log_size = snprintf(early_log_buffer + early_log_buf_off, log_space,
"(00.000000) ");
}
log_size += vsnprintf(early_log_buffer + early_log_buf_off + log_size,
sizeof(early_log_buffer) - early_log_buf_off - log_size, format, params);
if (log_size < log_space)
log_size += vsnprintf(early_log_buffer + early_log_buf_off + log_size,
log_space - log_size, format, params);
if (log_size > log_space) {
/* vsnprintf always add the terminating null byte. */
log_size = log_space - 1;
}
/* Save log entry size */
hdr->len = log_size;