xiaoxiang781216 commented on code in PR #16326:
URL: https://github.com/apache/nuttx/pull/16326#discussion_r2075885368
##########
fs/inode/fs_files.c:
##########
@@ -317,11 +331,36 @@ static int nx_dup3_from_tcb(FAR struct tcb_s *tcb, int
fd1, int fd2,
return -EBADF;
}
+ /* dup3() and dup2() dictate that fd2 must be closed prior to reuse */
+
+ filep = files_fget(list, fd2);
+ if (filep)
+ {
+ /* The file exists and is open, close it here */
+
+ fs_putfilep(filep);
+ file_close_wait(filep);
+ }
+
+ /* This should not fail now */
+
filep = files_fget_by_index(list,
fd2 / CONFIG_NFILE_DESCRIPTORS_PER_BLOCK,
fd2 % CONFIG_NFILE_DESCRIPTORS_PER_BLOCK,
&new);
+ /* If return value is NULL, it means the file is partially open. This means
+ * the userspace is racing against itself. To prevent the kernel from
+ * crashing due to access to invalid file pointer, just make the user try
Review Comment:
but the spec require that open/close is
atomic(https://man7.org/linux/man-pages/man2/dup.2.html):
```
If the file descriptor newfd was previously open, it is closed
before being reused; the close is performed silently (i.e., any
errors during the close are not reported by dup2()).
The steps of closing and reusing the file descriptor newfd are
performed atomically. This is important, because trying to
implement equivalent functionality using
[close(2)](https://man7.org/linux/man-pages/man2/close.2.html) and dup() would
be subject to race conditions, whereby newfd might be reused
between the two steps. Such reuse could happen because the main
program is interrupted by a signal handler that allocates a file
descriptor, or because a parallel thread allocates a file
descriptor.
```
and shouldn't return the error code(e.g. -EBUSY) in this case.
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