[PATCH RESEND 10/11] splice: file->pipe: -EINVAL for non-regular files w/o FMODE_NOWAIT

[Ahelenia Ziemiańska]

We request non-blocking I/O in the generic implementation, but some
files ‒ ttys ‒ only check O_NONBLOCK. Refuse them here, lest we
risk sleeping with the pipe locked for indeterminate lengths of
time.

This also masks inconsistent wake-ups (usually every second line)
when splicing from ttys in icanon mode.

Regular files don't /have/ a distinct O_NONBLOCK mode,
because they always behave non-blockingly, and for them FMODE_NOWAIT is
used in the purest sense of
  /* File is capable of returning -EAGAIN if I/O will block */
which is not set by the vast majority of filesystems,
and it's not the semantic we want here.

Link: https://lore.kernel.org/linux-fsdevel/qk6hjuam54khlaikf2ssom6custxf5is2ekkaequf4hvode3ls@zgf7j5j4ubvw/t/#u
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@xxxxxxxxxxxxxxxxxx>
---
 fs/splice.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/splice.c b/fs/splice.c
index 9d29664f23ee..81788bf7daa1 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -1300,6 +1300,8 @@ long do_splice(struct file *in, loff_t *off_in, struct file *out,
 	} else if (opipe) {
 		if (off_out)
 			return -ESPIPE;
+		if (!((in->f_mode & FMODE_NOWAIT) || S_ISREG(in->f_inode->i_mode)))
+			return -EINVAL;
 		if (off_in) {
 			if (!(in->f_mode & FMODE_PREAD))
 				return -EINVAL;
-- 
2.39.2

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