On Mon, Feb 01, 2010 at 10:18:27PM +0100, Jim Meyering wrote:
>
> In src/qemu/qemu_driver.c, coverity reports this:
>
> Event negative_return_fn: Called negative-returning function "lseek(logfile, 0L, 2)"
> Event var_assign: NEGATIVE return value of "lseek" assigned to signed variable "pos"
> At conditional (1): "(pos = lseek(logfile, 0L, 2)) < 0" taking true path
> 2877 if ((pos = lseek(logfile, 0, SEEK_END)) < 0)
> 2878 VIR_WARN(_("Unable to seek to end of logfile: %s"),
> 2879 virStrerror(errno, ebuf, sizeof ebuf));
>
> since later in that same function, a negative "pos" may
> be used like this:
>
> Event negative_returns: Tracked variable "pos" was passed to a negative sink. [details]
> 2930 if (qemudWaitForMonitor(conn, driver, vm, pos) < 0)
> 2931 goto abort;
> 2932
>
> which is a legitimate problem, since
> qemudWaitForMonitor calls qemudLogReadFD, which calls lseek
> with that same "pos" value:
>
> Event neg_sink_parm_call: Parameter "pos" passed to negative sink "lseek"
> 560 if (lseek(fd, pos, SEEK_SET) < 0) {
> 561 virReportSystemError(conn, errno,
> 562 _("Unable to seek to %lld in %s"),
> 563 (long long) pos, logfile);
> 564 close(fd);
> 565 }
>
>
> One approach is to detect the negative offset in that final bit
> of code and skip the lseek:
>
> >From 0ef617935462c314ed0b44bcaa3dd5bf58ccbc1b Mon Sep 17 00:00:00 2001
> From: Jim Meyering <meyering@xxxxxxxxxx>
> Date: Mon, 1 Feb 2010 22:17:44 +0100
> Subject: [PATCH] avoid a probable EINVAL from lseek
>
> * src/qemu/qemu_driver.c (qemudLogReadFD): Don't pass a negative
> offset (from a preceding failed attempt to seek to EOF) to this use
> of lseek.
> ---
> src/qemu/qemu_driver.c | 4 ++--
> 1 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 22593bf..676a27b 100644
> --- a/src/qemu/qemu_driver.c
> +++ b/src/qemu/qemu_driver.c
> @@ -558,8 +558,8 @@ qemudLogReadFD(virConnectPtr conn, const char* logDir, const char* name, off_t p
> close(fd);
> return -1;
> }
> - if (lseek(fd, pos, SEEK_SET) < 0) {
> - virReportSystemError(conn, errno,
> + if (pos < 0 || lseek(fd, pos, SEEK_SET) < 0) {
> + virReportSystemError(conn, pos < 0 ? 0 : errno,
> _("Unable to seek to %lld in %s"),
> (long long) pos, logfile);
> close(fd);
I was wondering if it wasn't simpler to abort earlier on when
pos < 0 was returned from lseek, but after rereading the code I
agree with your patch,
ACK,
Daniel
--
Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
daniel@xxxxxxxxxxxx | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library http://libvirt.org/
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