rbd: make coverity happy

A recent coverity run found two "defects" in rbd.cc:

** CID 1138367:  Time of check time of use  (TOCTOU)
/rbd.cc: 2024 in do_kernel_rm(const char *)()

2019   const char *fname = "/sys/bus/rbd/remove_single_major";
2020   if (stat(fname, &sbuf)) {
2021     fname = "/sys/bus/rbd/remove";
2022   }
2023
2024   int fd = open(fname, O_WRONLY);
2025   if (fd < 0) {

** CID 1138368:  Time of check time of use  (TOCTOU)
/rbd.cc: 1735 in do_kernel_add(const char *, const char *, const char *)()

same as above, s/remove/add

There is nothing racey going on here, and this is not an instance of
TOCTOU, but, instead of silencing coverity with annotatations, redo
this with two open() calls.

Signed-off-by: Ilya Dryomov <ilya.dryomov@inktank.com>

diff --git a/src/rbd.cc b/src/rbd.cc
index f9d3b65dac79782f3b9e08b5d87ecb6c9669a71d..6a8e6029a262dd03887e56702c1c1f609489809f 100644 (file)
--- a/src/rbd.cc
+++ b/src/rbd.cc
@@ -1720,27 +1720,29 @@ static int do_kernel_add(const char *poolname, const char *imgname,
     }
   }
 
-  // 'add' interface is deprecated, see if 'add_single_major' is
-  // available and use it if it is
+  // 'add' interface is deprecated, use 'add_single_major' if it's
+  // available
   //
   // ('add' and 'add_single_major' interfaces are identical, except
   // that if rbd kernel module is new enough and is configured to use
   // single-major scheme, 'add' is disabled in order to prevent old
   // userspace from doing weird things at unmap time)
-  const char *fname = "/sys/bus/rbd/add_single_major";
-  if (stat(fname, &sb)) {
-    fname = "/sys/bus/rbd/add";
-  }
-
-  int fd = open(fname, O_WRONLY);
+  int fd = open("/sys/bus/rbd/add_single_major", O_WRONLY);
   if (fd < 0) {
-    r = -errno;
-    if (r == -ENOENT) {
-      cerr << "rbd: /sys/bus/rbd/add does not exist!" << std::endl
-          << "Did you run 'modprobe rbd' or is your rbd module too old?"
-          << std::endl;
+    if (errno == ENOENT) {
+      fd = open("/sys/bus/rbd/add", O_WRONLY);
+      if (fd < 0) {
+        r = -errno;
+        if (r == -ENOENT) {
+          cerr << "rbd: /sys/bus/rbd/add does not exist!" << std::endl
+               << "Did you run 'modprobe rbd' or is your rbd module too old?"
+               << std::endl;
+        }
+        return r;
+      }
+    } else {
+      return -errno;
     }
-    return r;
   }
 
   string add = oss.str();
@@ -2016,14 +2018,15 @@ static int do_kernel_rm(const char *dev)
 
   // see comment in do_kernel_add(), same goes for 'remove' vs
   // 'remove_single_major'
-  const char *fname = "/sys/bus/rbd/remove_single_major";
-  if (stat(fname, &sbuf)) {
-    fname = "/sys/bus/rbd/remove";
-  }
-
-  int fd = open(fname, O_WRONLY);
+  int fd = open("/sys/bus/rbd/remove_single_major", O_WRONLY);
   if (fd < 0) {
-    return -errno;
+    if (errno == ENOENT) {
+      fd = open("/sys/bus/rbd/remove", O_WRONLY);
+      if (fd < 0)
+        return -errno;
+    } else {
+      return -errno;
+    }
   }
 
   r = safe_write(fd, seq_num.c_str(), seq_num.size());