From: David Howells dhowells@redhat.com
[ Upstream commit 6c77676645ad42993e0a8bdb8dafa517851a352a ]
The maths at the end of iter_xarray_get_pages() to calculate the actual size doesn't work under some circumstances, such as when it's been asked to extract a partial single page. Various terms of the equation cancel out and you end up with actual == offset. The same issue exists in iter_xarray_get_pages_alloc().
Fix these to just use min() to select the lesser amount from between the amount of page content transcribed into the buffer, minus the offset, and the size limit specified.
This doesn't appear to have caused a problem yet upstream because network filesystems aren't getting the pages from an xarray iterator, but rather passing it directly to the socket, which just iterates over it. Cachefiles *does* do DIO from one to/from ext4/xfs/btrfs/etc. but it always asks for whole pages to be written or read.
Fixes: 7ff5062079ef ("iov_iter: Add ITER_XARRAY") Reported-by: Jeff Layton jlayton@kernel.org Signed-off-by: David Howells dhowells@redhat.com cc: Alexander Viro viro@zeniv.linux.org.uk cc: Dominique Martinet asmadeus@codewreck.org cc: Mike Marshall hubcap@omnibond.com cc: Gao Xiang xiang@kernel.org cc: linux-afs@lists.infradead.org cc: v9fs-developer@lists.sourceforge.net cc: devel@lists.orangefs.org cc: linux-erofs@lists.ozlabs.org cc: linux-cachefs@redhat.com cc: linux-fsdevel@vger.kernel.org Signed-off-by: Al Viro viro@zeniv.linux.org.uk Signed-off-by: Sasha Levin sashal@kernel.org --- lib/iov_iter.c | 20 ++++---------------- 1 file changed, 4 insertions(+), 16 deletions(-)
diff --git a/lib/iov_iter.c b/lib/iov_iter.c index 6d146f77601d..be07eb24ab2f 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -1436,7 +1436,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, { unsigned nr, offset; pgoff_t index, count; - size_t size = maxsize, actual; + size_t size = maxsize; loff_t pos;
if (!size || !maxpages) @@ -1463,13 +1463,7 @@ static ssize_t iter_xarray_get_pages(struct iov_iter *i, if (nr == 0) return 0;
- actual = PAGE_SIZE * nr; - actual -= offset; - if (nr == count && size > 0) { - unsigned last_offset = (nr > 1) ? 0 : offset; - actual -= PAGE_SIZE - (last_offset + size); - } - return actual; + return min(nr * PAGE_SIZE - offset, maxsize); }
/* must be done on non-empty ITER_IOVEC one */ @@ -1604,7 +1598,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i, struct page **p; unsigned nr, offset; pgoff_t index, count; - size_t size = maxsize, actual; + size_t size = maxsize; loff_t pos;
if (!size) @@ -1633,13 +1627,7 @@ static ssize_t iter_xarray_get_pages_alloc(struct iov_iter *i, if (nr == 0) return 0;
- actual = PAGE_SIZE * nr; - actual -= offset; - if (nr == count && size > 0) { - unsigned last_offset = (nr > 1) ? 0 : offset; - actual -= PAGE_SIZE - (last_offset + size); - } - return actual; + return min(nr * PAGE_SIZE - offset, maxsize); }
ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,