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.

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1169055

Signed-off-by: Eric Blake <eblake@redhat.com>

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index a956c5928de5c388175b3fe0b1d614e39909b330..ec93191d2cd64dbfdb4a3089a5865b6bea0e1888 100644 (file)
--- 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
@@ -1324,22 +1324,13 @@ 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,
+    if (!pidinfo ||
+        fscanf(pidinfo,
                /* pid -> stime */
                "%*d %*s %*c %*d %*d %*d %*d %*d %*u %*u %*u %*u %*u %llu %llu"
                /* cutime -> endcode */
@@ -1347,10 +1338,7 @@ qemuGetProcessInfo(unsigned long long *cpuTime, int *lastCpu, long *vm_rss,
                /* startstack -> processor */
                "%*u %*u %*u %*u %*u %*u %*u %*u %*u %*u %*d %d",
                &usertime, &systime, &rss, &cpu) != 4) {
-        VIR_FORCE_FCLOSE(pidinfo);
         VIR_WARN("cannot parse process status data");
-        errno = -EINVAL;
-        return -1;
     }
 
     /* We got jiffies
@@ -1359,7 +1347,8 @@ qemuGetProcessInfo(unsigned long long *cpuTime, int *lastCpu, long *vm_rss,
      * So calculate thus....
      */
     if (cpuTime)
-        *cpuTime = 1000ull * 1000ull * 1000ull * (usertime + systime) / (unsigned long long)sysconf(_SC_CLK_TCK);
+        *cpuTime = 1000ull * 1000ull * 1000ull * (usertime + systime)
+            / (unsigned long long)sysconf(_SC_CLK_TCK);
     if (lastCpu)
         *lastCpu = cpu;