Re: [Libguestfs] [PATCH 2/2] daemon: Always reflect command stderr to stderr when debugging.
Richard W.M. Jones wrote:
Subject: [PATCH 2/2] daemon: Always reflect command stderr to stderr
when debugging.
When debugging (ie. LIBGUESTFS_DEBUG=1 & verbose flag set in daemon)
always reflect any stderr output from commands that we run to
stderr of the daemon, so it is visible.
Previously if stderror == NULL in command*, stderr output was
just eaten and discarded which meant useful error messages could
be lost.
---
daemon/guestfsd.c | 25 ++++++++++++++++---------
1 files changed, 16 insertions(+), 9 deletions(-)
diff --git a/daemon/guestfsd.c b/daemon/guestfsd.c
index bf06c73..370eea8 100644
--- a/daemon/guestfsd.c
+++ b/daemon/guestfsd.c
@@ -38,6 +38,8 @@
#include <printf.h>
#include "c-ctype.h"
+#include "ignore-value.h"
+
#include "daemon.h"
static char *read_cmdline (void);
@@ -742,15 +744,20 @@ commandrvf (char **stdoutput, char **stderror, int flags,
}
if (r == 0) { FD_CLR (se_fd[0], &rset); quit++; }
- if (r > 0 && stderror) {
- se_size += r;
- p = realloc (*stderror, se_size);
- if (p == NULL) {
- perror ("realloc");
- goto quit;
- }
- *stderror = p;
- memcpy (*stderror + se_size - r, buf, r);
+ if (r > 0) {
+ if (verbose)
+ ignore_value (write (2, buf, r));
+
+ if (stderror) {
+ se_size += r;
+ p = realloc (*stderror, se_size);
+ if (p == NULL) {
+ perror ("realloc");
+ goto quit;
+ }
+ *stderror = p;
+ memcpy (*stderror + se_size - r, buf, r);
Hi Rich,
This change looks fine.
However, there's an unrelated problem:
if stderr is very large, incrementing se_size by "r"
could result in a smaller total size (overflow).
Then, the following memcpy would clobber the heap
by writing a potentially very large amount of data
into a much smaller (or even 0-length) buffer.
One way to avoid it:
size_t new_size = se_size + r;
if (new_size < se_size) {
perror ("standard error too large");
goto quit;
}
se_size = new_size;
Or perhaps better: limit the buffer size to say 1MiB,
and warn if truncation is required.