On 03/21/2011 02:20 AM, Daniel Veillard wrote:
On Fri, Mar 18, 2011 at 08:31:22PM -0600, Eric Blake wrote:
Valgrind caught that our log wrap-around was going 1 past the end. Regression introduced in commit b16f47a; previously the buffer was static and size+1 bytes, but now it is dynamic and exactly size bytes.
* src/util/logging.c (virLogStr): Don't write past end of log. ---
An alternative would be to malloc one larger; but since the log is likely to be a page size multiple and large enough to be worth malloc using mmap, going one larger is likely to waste the bulk of a page. Also, I like always NUL-terminating the current end of the log (without including that NUL in the log length).
src/util/logging.c | 4 ++-- 1 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/src/util/logging.c b/src/util/logging.c index b972f8a..f4910ad 100644 --- a/src/util/logging.c +++ b/src/util/logging.c @@ -326,7 +326,7 @@ static void virLogStr(const char *str, int len) { return; if (len <= 0) len = strlen(str); - if (len > virLogSize) + if (len >= virLogSize) return; virLogLock();
@@ -336,13 +336,13 @@ static void virLogStr(const char *str, int len) { if (virLogEnd + len >= virLogSize) { tmp = virLogSize - virLogEnd; memcpy(&virLogBuffer[virLogEnd], str, tmp); - virLogBuffer[virLogSize] = 0; memcpy(&virLogBuffer[0], &str[tmp], len - tmp); virLogEnd = len - tmp; } else { memcpy(&virLogBuffer[virLogEnd], str, len); virLogEnd += len; } + virLogBuffer[virLogEnd] = 0; /* * Update the log length, and if full move the start index */
Well, I tend to prefer having a 0 at the end of character arrays in C, this can be useful for example when debugging, so slightly preferring one extra byte malloc for safety, either way not a big deal, but let's fix this,
I see two ways to do things - either malloc an extra byte (which will always be NUL from the malloc, so deleting 'virLogBuffer[virLogSize] = 0' is still okay), or by touching the rest of the code to always leave virLogBuffer[virLogSize-1] as NUL (more invasive, and caps the useful log to virLogSize-1). Do you want me to prepare a followup patch, and if so, for which of those two options?
ACK
I went ahead and pushed this as-is to avoid the invalid write; we can do further cleanup based on how we answer the above question if we want to guarantee a NUL byte at the end of the array for debugging purposes. -- Eric Blake eblake@redhat.com +1-801-349-2682 Libvirt virtualization library http://libvirt.org