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



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);
--
1.7.0.rc1.149.g0b0b7


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