linux-kernel - [PATCH] iov_iter: Four fixes for ITER

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Message-ID: <3545034.1619392490@warthog.procyon.org.uk>
Date:   Mon, 26 Apr 2021 00:14:50 +0100
From:   David Howells <dhowells@...hat.com>
To:     Alexander Viro <viro@...iv.linux.org.uk>
Cc:     dhowells@...hat.com, linux-fsdevel@...r.kernel.org,
        Dave Wysochanski <dwysocha@...hat.com>,
        Marc Dionne <marc.dionne@...istor.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Christoph Hellwig <hch@....de>, linux-mm@...ck.org,
        linux-cachefs@...hat.com, linux-afs@...ts.infradead.org,
        linux-nfs@...r.kernel.org, linux-cifs@...r.kernel.org,
        ceph-devel@...r.kernel.org, v9fs-developer@...ts.sourceforge.net,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Anna Schumaker <anna.schumaker@...app.com>,
        Steve French <sfrench@...ba.org>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Jeff Layton <jlayton@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] iov_iter: Four fixes for ITER_XARRAY

Hi Al,

I think this patch should include all the fixes necessary.  I could merge
it in, but I think it might be better to tag it on the end as an additional
patch.

David
---
iov_iter: Four fixes for ITER_XARRAY

Fix four things[1] in the patch that adds ITER_XARRAY[2]:

 (1) Remove the address_space struct predeclaration.  This is a holdover
     from when it was ITER_MAPPING.

 (2) Fix _copy_mc_to_iter() so that the xarray segment updates count and
     iov_offset in the iterator before returning.

 (3) Fix iov_iter_alignment() to not loop in the xarray case.  Because the
     middle pages are all whole pages, only the end pages need be
     considered - and this can be reduced to just looking at the start
     position in the xarray and the iteration size.

 (4) Fix iov_iter_advance() to limit the size of the advance to no more
     than the remaining iteration size.

Reported-by: Al Viro <viro@...iv.linux.org.uk>
Signed-off-by: David Howells <dhowells@...hat.com>
Link: https://lore.kernel.org/r/YIVrJT8GwLI0Wlgx@zeniv-ca.linux.org.uk [1]
Link: https://lore.kernel.org/r/161918448151.3145707.11541538916600921083.stgit@warthog.procyon.org.uk [2]
---
 include/linux/uio.h |    1 -
 lib/iov_iter.c      |    5 +++++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/uio.h b/include/linux/uio.h
index 5f5ffc45d4aa..d3ec87706d75 100644
--- a/include/linux/uio.h
+++ b/include/linux/uio.h
@@ -10,7 +10,6 @@
 #include <uapi/linux/uio.h>
 
 struct page;
-struct address_space;
 struct pipe_inode_info;
 
 struct kvec {
diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 44fa726a8323..61228a6c69f8 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -791,6 +791,8 @@ size_t _copy_mc_to_iter(const void *addr, size_t bytes, struct iov_iter *i)
 			curr_addr = (unsigned long) from;
 			bytes = curr_addr - s_addr - rem;
 			rcu_read_unlock();
+			i->iov_offset += bytes;
+			i->count -= bytes;
 			return bytes;
 		}
 		})
@@ -1147,6 +1149,7 @@ void iov_iter_advance(struct iov_iter *i, size_t size)
 		return;
 	}
 	if (unlikely(iov_iter_is_xarray(i))) {
+		size = min(size, i->count);
 		i->iov_offset += size;
 		i->count -= size;
 		return;
@@ -1346,6 +1349,8 @@ unsigned long iov_iter_alignment(const struct iov_iter *i)
 			return size | i->iov_offset;
 		return size;
 	}
+	if (unlikely(iov_iter_is_xarray(i)))
+		return (i->xarray_start + i->iov_offset) | i->count;
 	iterate_all_kinds(i, size, v,
 		(res |= (unsigned long)v.iov_base | v.iov_len, 0),
 		res |= v.bv_offset | v.bv_len,