Revert "rootdev: Don't try to access /dev/block."

This breaks when built with clang
This reverts commit 4a2bdd8006a5ddf166bcc8973c135799da453e09.

Change-Id: I2f89a9c19de91d4c46dce110e36a32551134e5d5

2 files changed, 11 insertions, 8 deletions

diff --git a/rootdev.c b/rootdev.c
index 82e423f..f0de1ff 100644
--- a/rootdev.c
+++ b/rootdev.c
@@ -357,10 +357,11 @@ int rootdev_get_path(char *path, size_t size, const char *device,
   if (path_len != strlen(dev_path) + 1 + strlen(device))
     return -1;
 
-  // TODO(bsimonnet): We should check that |path| exists and is the right
-  // device. We don't do this currently as OEMs can add custom SELinux rules
-  // which may prevent us from accessing this.
-  // See b/24267261.
+  if (stat(path, &dev_statbuf) != 0)
+    return 1;
+
+  if (dev && dev != dev_statbuf.st_rdev)
+    return 2;
 
   return 0;
 }
diff --git a/rootdev.h b/rootdev.h
index 05c3da1..74a48da 100644
--- a/rootdev.h
+++ b/rootdev.h
@@ -79,12 +79,14 @@ void rootdev_get_device_slave(char *slave, size_t size, dev_t *dev,
  * @path is populated for all return codes.
  * Returns 0 on success and non-zero on error:
  * -1 on unexpected errors (@path may be invalid)
+ *  1 on no existing @path
+ *  2 @path exists but the dev_t value is mismatched.
  *
  * Nb, this function does NOT search /dev for a match.  It performs a normal
- *     string concatenation.
- *     We can't check if the device actually exists as vendors may create an
- *     SELinux context we don't know about for it (in which case, this function
- *     would always fail).
+ *     string concatenation and probes for the existence.  If udev has moved,
+ *     or otherwise renamed, the device, a positive value is returned.
+ *     The caller may then use the dev_t and @path to create the node with
+ *     mknod(2).
  */
 int rootdev_get_path(char *path, size_t size, const char *device, dev_t dev,
                      const char *dev_path);