On 17.04.23 06:46, Hugh Dickins wrote:
generic_file_splice_read() makes a couple of preliminary checks (for
s_maxbytes and zero len), but shmem_file_splice_read() is called without
those: so check them inside it. (But shmem does not support O_DIRECT,
so no need for that one here - and even if O_DIRECT support were stubbed
in, it would still just be using the page cache.)
HWPoison: my reading of folio_test_hwpoison() is that it only tests the
head page of a large folio, whereas splice_folio_into_pipe() will splice
as much of the folio as it can: so for safety we should also check the
has_hwpoisoned flag, set if any of the folio's pages are hwpoisoned.
(Perhaps that ugliness can be improved at the mm end later.)
The call to splice_zeropage_into_pipe() risked overrunning past EOF:
ask it for "part" not "len".
Fixes: b81d7b89becc ("shmem: Implement splice-read")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
Thank you, David, for attending to tmpfs in your splice update:
yes, I too wish it could have just used the generic, but I'm sure
you're right that there's a number of reasons it needs its own.
mm/shmem.c | 14 +++++++++++---
1 file changed, 11 insertions(+), 3 deletions(-)
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -2902,6 +2902,11 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
loff_t isize;
int error = 0;
+ if (unlikely(*ppos >= MAX_LFS_FILESIZE))
+ return 0;
+ if (unlikely(!len))
+ return 0;
+
/* Work out how much data we can actually add into the pipe */
used = pipe_occupancy(pipe->head, pipe->tail);
npages = max_t(ssize_t, pipe->max_usage - used, 0);
@@ -2911,7 +2916,8 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
if (*ppos >= i_size_read(inode))
break;
- error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio, SGP_READ);
+ error = shmem_get_folio(inode, *ppos / PAGE_SIZE, &folio,
+ SGP_READ);
if (error) {
if (error == -EINVAL)
error = 0;
@@ -2920,7 +2926,9 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
if (folio) {
folio_unlock(folio);
- if (folio_test_hwpoison(folio)) {
+ if (folio_test_hwpoison(folio) ||
+ (folio_test_large(folio) &&
+ folio_test_has_hwpoisoned(folio))) {
error = -EIO;
break;
}
@@ -2956,7 +2964,7 @@ static ssize_t shmem_file_splice_read(struct file *in, loff_t *ppos,
folio_put(folio);
folio = NULL;
} else {
- n = splice_zeropage_into_pipe(pipe, *ppos, len);
+ n = splice_zeropage_into_pipe(pipe, *ppos, part);
}
if (!n)
FWIW, looks good to me.
--
Thanks,
David / dhildenb
