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fs: check FMODE_LSEEK to control internal pipe splicing

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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 is an okayish heuristic, but it doesn't totally work. For example,
a few chardevs should be spliceable here. And a few regular files
shouldn't. This patch fixes this by instead checking whether FMODE_LSEEK
is set, which represents decently enough what we need rewinding for when
splicing to internal pipes.

Fixes: b92ce55893 ("[PATCH] splice: add direct fd <-> fd splicing support")
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Jason A. Donenfeld 2022-06-29 15:06:58 +02:00 committed by Al Viro
parent 54ef7a47f6
commit 97ef77c52b
1 changed files with 4 additions and 6 deletions
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10
fs/splice.c
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@ -814,17 +814,15 @@ ssize_t splice_direct_to_actor(struct file *in, struct splice_desc *sd,
{
struct pipe_inode_info *pipe;
long ret, bytes;
umode_t i_mode;
size_t len;
int i, flags, more;
/*
* We require the input being a regular file, as we don't want to
* randomly drop data for eg socket -> socket splicing. Use the
* piped splicing for that!
* We require the input to be seekable, as we don't want to randomly
* drop data for eg socket -> socket splicing. Use the piped splicing
* for that!
*/
i_mode = file_inode(in)->i_mode;
if (unlikely(!S_ISREG(i_mode) && !S_ISBLK(i_mode)))
if (unlikely(!(in->f_mode & FMODE_LSEEK)))
return -EINVAL;
/*