[PATCH 6.6.y] smb: client: discard post-EOF pagecache when extending a file via zero range

[Sasha Levin <sashal@kernel.org>]

From: Paulo Alcantara <pc@manguebit.org>

[ Upstream commit da4fe97fb6c730d9c94a115c7bfa6f98e0d578d0 ]

smb3_zero_range() removed the pagecache only for the range being zeroed,
so when it extends the file the folio straddling the old EOF - which may
hold data dirtied past EOF through an mmap - was never dropped and became
visible as file content once the file was extended.

Lower the discard boundary to the smaller of the zero-range offset and the
old EOF.

Fixes: 72c419d9b073 ("cifs: fix smb3_zero_range so it can expand the file-size when required")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org
[ sashal: Adjusted context due to the missing netfs_wait_for_outstanding_io() call. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/smb/client/smb2ops.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 887ffa77aa183..a82abe2e8ce14 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -3283,8 +3283,11 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 	/*
 	 * We zero the range through ioctl, so we need remove the page caches
 	 * first, otherwise the data may be inconsistent with the server.
+	 *
+	 * Start at the old EOF when extending so the folio straddling it, which
+	 * may hold data written past EOF through an mmap, is dropped too.
 	 */
-	truncate_pagecache_range(inode, offset, offset + len - 1);
+	truncate_pagecache_range(inode, min(offset, i_size), offset + len - 1);
 
 	/* if file not oplocked can't be sure whether asking to extend size */
 	rc = -EOPNOTSUPP;
-- 
2.53.0