fs/inode: Add shared permission helpers and pseudoFS open checks

Add fs_checkmode() and fs_checkopenperm() for reuse across filesystems.
Enforce pseudoFS mode bits in inode_checkperm() and allow world-readable
open of passwd/group entries so getpwnam() works after seteuid().

Signed-off-by: Abhishek Mishra <mishra.abhishek2808@gmail.com>

fs/inode/inode.h

@@ -422,6 +422,24 @@ void inode_release(FAR struct inode *inode);
  * Name: inode_checkperm
  *
  * Description:
+ *   Check 'inode' for 'amode' access on pseudo-filesystem inodes.
+ *   NULL 'inode' (root) and mountpoints are exempt.
+ *
+ * Input Parameters:
+ *   inode - Inode to check, or NULL for a root-level path
+ *   amode - Access mode bitmask (R_OK / W_OK / X_OK)
+ *
+ * Returned Value:
+ *   Zero (OK) on success, or -EACCES if permission is denied.
+ *
+ ****************************************************************************/
+
+int inode_checkperm(FAR struct inode *inode, int amode);
+
+/****************************************************************************
+ * Name: inode_checkopenperm
+ *
+ * Description:
  *   Validate open access to 'inode' for 'oflags'.  Checks driver operation
  *   support, then pseudo-filesystem mode bits when enabled.  Mountpoints
  *   are exempt from mode checks.
@@ -435,25 +453,13 @@ void inode_release(FAR struct inode *inode);
  *
  ****************************************************************************/
 
-int inode_checkperm(FAR struct inode *inode, int oflags);
+int inode_checkopenperm(FAR struct inode *inode, int oflags);
 
-/****************************************************************************
- * Name: inode_checkdirperm
- *
- * Description:
- *   Check parent directory 'dir' for 'amode' access on pseudo-filesystem
- *   inodes.  NULL 'dir' (root) and mountpoints are exempt.
- *
- * Input Parameters:
- *   dir   - Parent directory inode, or NULL for a root-level path
- *   amode - Access mode bitmask (R_OK / W_OK / X_OK)
- *
- * Returned Value:
- *   Zero (OK) on success, or -EACCES if permission is denied.
- *
- ****************************************************************************/
-
-int inode_checkdirperm(FAR struct inode *dir, int amode);
+#ifdef CONFIG_FS_PERMISSION
+int fs_checkmode(uid_t owner, gid_t group, mode_t mode, int amode);
+int fs_open_amode(int oflags);
+int fs_checkopenperm(uid_t owner, gid_t group, mode_t mode, int oflags);
+#endif
 
 /****************************************************************************
  * Name: foreach_inode

fs/vfs/fs_mkdir.c

@@ -142,7 +142,7 @@ int mkdir(const char *pathname, mode_t mode)
        * both W_OK and X_OK to create a directory entry.
        */
 
-      ret = inode_checkdirperm(desc.parent, W_OK | X_OK);
+      ret = inode_checkperm(desc.parent, W_OK | X_OK);
       if (ret < 0)
         {
           errcode = -ret;

fs/vfs/fs_open.c

@@ -172,7 +172,7 @@ static int file_vopen(FAR struct file *filep, FAR const char *path,
 
   /* Validate operation support and pseudo-filesystem permissions */
 
-  ret = inode_checkperm(inode, oflags);
+  ret = inode_checkopenperm(inode, oflags);
   if (ret < 0)
     {
       goto errout_with_inode;

fs/vfs/fs_rename.c

@@ -86,7 +86,7 @@ static int pseudorename(FAR const char *oldpath, FAR struct inode *oldinode,
 
   /* Verify source parent write permission. */
 
-  ret = inode_checkdirperm(oldparent, W_OK);
+  ret = inode_checkperm(oldparent, W_OK);
   if (ret < 0)
     {
       goto errout;
@@ -177,7 +177,7 @@ static int pseudorename(FAR const char *oldpath, FAR struct inode *oldinode,
   inode_find(&pardesc);   /* pardesc.parent valid even if node not found */
   parnode = pardesc.node;
 
-  ret = inode_checkdirperm(pardesc.parent, W_OK);
+  ret = inode_checkperm(pardesc.parent, W_OK);
 
   /* inode_find() holds a reference on parnode; RELEASE_SEARCH() only
    * frees pardesc.buffer.

fs/vfs/fs_unlink.c

@@ -123,7 +123,7 @@ int nx_unlink(FAR const char *pathname)
 
       /* Verify parent-directory write permission before unlink. */
 
-      ret = inode_checkdirperm(desc.parent, W_OK);
+      ret = inode_checkperm(desc.parent, W_OK);
       if (ret < 0)
         {
           goto errout_with_inode;