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(a)redhat.com&gt; > 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,