backing-file: use credential guards for splice write

Use credential guards for scoped credential override with automatic
restoration on scope exit.

Link: https://patch.msgid.link/20251103-work-creds-guards-simple-v1-6-a3e156839e7f@kernel.org
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/fs/backing-file.c b/fs/backing-file.c
index 4d4edf906ef34a30b669fe4d21c225ae431529c5..87ff918320c54add19a6960ee402e52f877fc368 100644 (file)
--- a/fs/backing-file.c
+++ b/fs/backing-file.c
@@ -303,7 +303,6 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
                                  size_t len, unsigned int flags,
                                  struct backing_file_ctx *ctx)
 {
-       const struct cred *old_cred;
        ssize_t ret;
 
        if (WARN_ON_ONCE(!(out->f_mode & FMODE_BACKING)))
@@ -316,11 +315,11 @@ ssize_t backing_file_splice_write(struct pipe_inode_info *pipe,
        if (ret)
                return ret;
 
-       old_cred = override_creds(ctx->cred);
-       file_start_write(out);
-       ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags);
-       file_end_write(out);
-       revert_creds(old_cred);
+       scoped_with_creds(ctx->cred) {
+               file_start_write(out);
+               ret = out->f_op->splice_write(pipe, out, &iocb->ki_pos, len, flags);
+               file_end_write(out);
+       }
 
        if (ctx->end_write)
                ctx->end_write(iocb, ret);