[Libguestfs] [PATCH 2/2] daemon: Always reflect command stderr to stderr when debugging.
Jim Meyering
jim at meyering.net
Mon Nov 9 10:35:55 UTC 2009
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.
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