From 79b496ebe382866e3a05090b7dc9ae95e85e65b2 Mon Sep 17 00:00:00 2001 From: Daehyeon Ko <4ncienth@gmail.com> Date: Sun, 18 Oct 2026 14:17:08 +0900 Subject: [PATCH] splice: avoid stale f_pos writeback on error do_splice() snapshots an implicit file position before calling the splice helper. Since splice does not take f_pos_lock, another operation on the same open file description can update f_pos while the helper is blocked. If the helper then fails, the unconditional writeback restores the stale snapshot. For a directory without ->splice_read, a file-to-pipe splice fails with -EINVAL. A concurrent directory mutation and getdents() call can advance f_pos and refresh the filesystem's revalidation cookie before that failure restores only the old position. The next ext2 readdir can then trust an offset inside a directory entry and copy data from the adjacent page to userspace. Only update an implicit file position when splice returns a non-negative result, matching read and write. Keep explicit offset updates unchanged. Fixes: 7995bd287134 ("splice: don't pass the address of ->f_pos to methods") Cc: stable@vger.kernel.org Signed-off-by: Daehyeon Ko <4ncienth@gmail.com> Link: https://patch.msgid.link/20261018051708.2422394-1-4ncienth@gmail.com Signed-off-by: Christian Brauner (Amutable) --- fs/splice.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/fs/splice.c b/fs/splice.c index bc243ab8dc43..f4bce3589067 100644 --- a/fs/splice.c +++ b/fs/splice.c @@ -1377,10 +1377,10 @@ ssize_t do_splice(struct file *in, loff_t *off_in, struct file *out, ret = do_splice_from(ipipe, out, &offset, len, flags); file_end_write(out); - if (!off_out) - out->f_pos = offset; - else + if (off_out) *off_out = offset; + else if (ret >= 0) + out->f_pos = offset; } else if (opipe) { if (off_out) return -ESPIPE; @@ -1401,10 +1401,10 @@ ssize_t do_splice(struct file *in, loff_t *off_in, struct file *out, ret = splice_file_to_pipe(in, opipe, &offset, len, flags); - if (!off_in) - in->f_pos = offset; - else + if (off_in) *off_in = offset; + else if (ret >= 0) + in->f_pos = offset; } else { ret = -EINVAL; }