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Re: [libvirt] [PATCH] avoid a probable EINVAL from lseek



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 redhat com>
> 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 veillard com  | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library  http://libvirt.org/


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