cachefiles: Fix the incorrect return value in __cachefiles_write()

[ Upstream commit 6b89819b06d8d339da414f06ef3242f79508be5e ]

In __cachefiles_write(), if the return value of the write operation > 0, it
is set to 0. This makes it impossible to distinguish scenarios where a
partial write has occurred, and will affect the outer calling functions:

 1) cachefiles_write_complete() will call "term_func" such as
netfs_write_subrequest_terminated(). When "ret" in __cachefiles_write()
is used as the "transferred_or_error" of this function, it can not
distinguish the amount of data written, makes the WARN meaningless.

 2) cachefiles_ondemand_fd_write_iter() can only assume all writes were
successful by default when "ret" is 0, and unconditionally return the full
length specified by user space.

Fix it by modifying "ret" to reflect the actual number of bytes written.
Furthermore, returning a value greater than 0 from __cachefiles_write()
does not affect other call paths, such as cachefiles_issue_write() and
fscache_write().

Fixes: 047487c947e8 ("cachefiles: Implement the I/O routines")
Signed-off-by: Zizhi Wo <wozizhi@huawei.com>
Link: https://lore.kernel.org/20250703024418.2809353-1-wozizhi@huaweicloud.com
Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/cachefiles/io.c b/fs/cachefiles/io.c
index 009d23cd435b544d2b7176c86a0f42eb4d2e2a4a..239a6002083d701f4e46b944942d7e02891fa453 100644 (file)
--- a/fs/cachefiles/io.c
+++ b/fs/cachefiles/io.c
@@ -346,8 +346,6 @@ int __cachefiles_write(struct cachefiles_object *object,
        default:
                ki->was_async = false;
                cachefiles_write_complete(&ki->iocb, ret);
-               if (ret > 0)
-                       ret = 0;
                break;
        }
 

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 3389a373faf6807db76b6681492d71a19f12f1d6..cfa8f23fdfb6558ed93755a9aeb3ddcd02053ed9 100644 (file)
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -84,10 +84,8 @@ static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
 
        trace_cachefiles_ondemand_fd_write(object, file_inode(file), pos, len);
        ret = __cachefiles_write(object, file, pos, iter, NULL, NULL);
-       if (!ret) {
-               ret = len;
+       if (ret > 0)
                kiocb->ki_pos += ret;
-       }
 
 out:
        fput(file);