[libvirt] [PATCH] Fix race condition in qemuGetProcessInfo
There is a race condition between the fopen and fscanf calls
in qemuGetProcessInfo. If fopen succeeds, there is a small
possibility that the file no longer exists before reading from it.
Now, if either fopen or fscanf calls fail, the function will behave
just as only fopen had failed.
---
src/qemu/qemu_driver.c | 43 ++++++++++++++++---------------------------
1 file changed, 16 insertions(+), 27 deletions(-)
diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index ad5f70a..9ab1a81 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -1310,9 +1310,9 @@ qemuGetProcessInfo(unsigned long long *cpuTime, int *lastCpu, long
*vm_rss,
{
char *proc;
FILE *pidinfo;
- unsigned long long usertime, systime;
- long rss;
- int cpu;
+ unsigned long long usertime = 0, systime = 0;
+ long rss = 0;
+ int cpu = 0;
int ret;
/* In general, we cannot assume pid_t fits in int; but /proc parsing
@@ -1324,33 +1324,24 @@ qemuGetProcessInfo(unsigned long long *cpuTime, int *lastCpu, long
*vm_rss,
if (ret < 0)
return -1;
- if (!(pidinfo = fopen(proc, "r"))) {
- /* VM probably shut down, so fake 0 */
- if (cpuTime)
- *cpuTime = 0;
- if (lastCpu)
- *lastCpu = 0;
- if (vm_rss)
- *vm_rss = 0;
- VIR_FREE(proc);
- return 0;
- }
+ pidinfo = fopen(proc, "r");
VIR_FREE(proc);
/* See 'man proc' for information about what all these fields are. We're
* only interested in a very few of them */
- if (fscanf(pidinfo,
- /* pid -> stime */
- "%*d %*s %*c %*d %*d %*d %*d %*d %*u %*u %*u %*u %*u %llu %llu"
- /* cutime -> endcode */
- "%*d %*d %*d %*d %*d %*d %*u %*u %ld %*u %*u %*u"
- /* startstack -> processor */
- "%*u %*u %*u %*u %*u %*u %*u %*u %*u %*u %*d %d",
- &usertime, &systime, &rss, &cpu) != 4) {
+ if (pidinfo) {
+ if (fscanf(pidinfo,
+ /* pid -> stime */
+ "%*d %*s %*c %*d %*d %*d %*d %*d %*u %*u %*u %*u %*u %llu
%llu"
+ /* cutime -> endcode */
+ "%*d %*d %*d %*d %*d %*d %*u %*u %ld %*u %*u %*u"
+ /* startstack -> processor */
+ "%*u %*u %*u %*u %*u %*u %*u %*u %*u %*u %*d %d",
+ &usertime, &systime, &rss, &cpu) != 4) {
+ VIR_WARN("cannot parse process status data");
+ usertime = systime = 0; rss = 0; cpu = 0;
+ }
VIR_FORCE_FCLOSE(pidinfo);
- VIR_WARN("cannot parse process status data");
- errno = -EINVAL;
- return -1;
}
/* We got jiffies
@@ -1374,8 +1365,6 @@ qemuGetProcessInfo(unsigned long long *cpuTime, int *lastCpu, long
*vm_rss,
VIR_DEBUG("Got status for %d/%d user=%llu sys=%llu cpu=%d rss=%ld",
(int) pid, tid, usertime, systime, cpu, rss);
- VIR_FORCE_FCLOSE(pidinfo);
-
return 0;
}
--
1.7.9.5