pussuw commented on code in PR #16326:
URL: https://github.com/apache/nuttx/pull/16326#discussion_r2076153514
##########
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):
Yes I know this very well. open/close/dup is a minefield of race conditions
and there is no known good way to handle it. My motivation was to prevent the
kernel from crashing if the user app is poorly made. I did this with the
minimal effort to the current implementation. This removes a kernel crash when
using dup & close. I can leave this downstream if the solution is not
acceptable.
> and shouldn't return the error code(e.g. -EBUSY) in this case.
As per the -EBUSY return value, we could handle EBUSY in libc, so the user
doesn't see this. This would be a completely POSIX compliant solution.
> and shouldn't return the error code
Btw, a newer POSIX spec allows returning -1 to user, but doesn't mention
EBUSY. We could return -1 and not touch errno ?
`If the close operation fails to close fildes2, dup2() shall return -1
without changing the open file description to which fildes2 refers. [1]`
[1] https://pubs.opengroup.org/onlinepubs/9699919799/functions/dup.html
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