coredump: fix error handling for replace_fd()

JIRA: https://issues.redhat.com/browse/RHEL-113598

commit 95c5f43
Author: Christian Brauner <brauner@kernel.org>
Date:   Mon, 14 Apr 2025 15:55:06 +0200

    coredump: fix error handling for replace_fd()

    The replace_fd() helper returns the file descriptor number on success
    and a negative error code on failure. The current error handling in
    umh_pipe_setup() only works because the file descriptor that is replaced
    is zero but that's pretty volatile. Explicitly check for a negative
    error code.

    Link: https://lore.kernel.org/20250414-work-coredump-v2-2-685bf231f828@kernel.org
    Tested-by: Luca Boccassi <luca.boccassi@gmail.com>
    Reviewed-by: Oleg Nesterov <oleg@redhat.com>
    Signed-off-by: Christian Brauner <brauner@kernel.org>

Signed-off-by: Waiman Long <longman@redhat.com>

Author: Waiman-Long

fs/coredump.c

@@ -507,18 +507,23 @@ static int umh_pipe_setup(struct subprocess_info *info, struct cred *new)
 {
 	struct file *files[2];
 	struct coredump_params *cp = (struct coredump_params *)info->data;
-	int err = create_pipe_files(files, 0);
+	int err;
+
+	err = create_pipe_files(files, 0);
 	if (err)
 		return err;
 
 	cp->file = files[1];
 
 	err = replace_fd(0, files[0], 0);
 	fput(files[0]);
+	if (err < 0)
+		return err;
+
 	/* and disallow core files too */
 	current->signal->rlim[RLIMIT_CORE] = (struct rlimit){1, 1};
 
-	return err;
+	return 0;
 }
 
 void do_coredump(const kernel_siginfo_t *siginfo)