linux-kernel - [PATCH RESEND for-al-viro] splice: allow direct splicing with chardevs

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Date:   Fri, 24 Jun 2022 14:48:52 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     linux-kernel@...r.kernel.org, viro@...iv.linux.org.uk
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH RESEND for-al-viro] splice: allow direct splicing with chardevs

The original direct splicing mechanism from Jens required the input to
be a regular file because it was avoiding the special socket case. It
also recognized blkdevs as being close enough to a regular file. But it
forgot about chardevs, which behave the same way and work fine here.

This commit adds the missing S_ISCHR condition so that chardevs such as
/dev/urandom can be directly spliced without strangely returning
-EINVAL.

Fixes: b92ce5589374 ("[PATCH] splice: add direct fd <-> fd splicing support")
Reviewed-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
---
Resending this with Jens' reviewed-by attached (he wrote the original
code this patch modifies). The prior submission seems to have been
buried/forgotten. This is presumably for Al's tree, though if somebody
else wants to take it, I'd be happy to get it in anywhere. The prior
forgotten thread is here for reference:
https://lore.kernel.org/lkml/20220520095747.123748-1-Jason@zx2c4.com/T/#u

 fs/splice.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/splice.c b/fs/splice.c
index 047b79db8eb5..7e673b1786fb 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -824,7 +824,7 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
 	 * piped splicing for that!
 	 */
 	i_mode = file_inode(in)->i_mode;
-	if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
+	if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode) && !S_ISCHR(i_mode)))
 		return -EINVAL;
 
 	/*
-- 
2.35.1