[2/8] cachefiles: Fix incorrect length return value in cachefiles_ondemand_fd_write_iter()

Commit Message

Zizhi Wo Aug. 21, 2024, 2:42 a.m. UTC

In the current on-demand loading mode, cachefiles_ondemand_fd_write_iter()
function first aligns "pos" and "len" to block boundaries. When calling
__cachefiles_write(), the aligned "pos" is passed in, but "len" is the
original unaligned value(iter->count). Additionally, the returned length of
the write operation is the modified "len" aligned by block size, which is
unreasonable.

The alignment of "pos" and "len" is intended only to check whether the
cache has enough space in erofs ondemand mode. But the modified len should
not be used as the return value of cachefiles_ondemand_fd_write_iter().
Doing so would result in a mismatch in the data written on-demand. For
example, if the length of the user state passed in is not aligned to the
block size (the preread scene / DIO writes only need 512 alignment), the
length of the write will differ from the actual length of the return.

To solve this issue, since the __cachefiles_prepare_write() modifies the
size of "len", we pass "aligned_len" to __cachefiles_prepare_write() to
calculate the free blocks and use the original "len" as the return value of
cachefiles_ondemand_fd_write_iter().

Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie")
Signed-off-by: Zizhi Wo <[e-mail]>
---
 fs/cachefiles/ondemand.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Patch

diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
index 470c96658385..bdd321017f1c 100644
--- a/fs/cachefiles/ondemand.c
+++ b/fs/cachefiles/ondemand.c
@@ -61,7 +61,7 @@  static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
 	struct cachefiles_object *object = kiocb->ki_filp->private_data;
 	struct cachefiles_cache *cache = object->volume->cache;
 	struct file *file = object->file;
-	size_t len = iter->count;
+	size_t len = iter->count, aligned_len = len;
 	loff_t pos = kiocb->ki_pos;
 	const struct cred *saved_cred;
 	int ret;
@@ -70,7 +70,7 @@  static ssize_t cachefiles_ondemand_fd_write_iter(struct kiocb *kiocb,
 		return -ENOBUFS;
 
 	cachefiles_begin_secure(cache, &saved_cred);
-	ret = __cachefiles_prepare_write(object, file, &pos, &len, len, true);
+	ret = __cachefiles_prepare_write(object, file, &pos, &aligned_len, len, true);
 	cachefiles_end_secure(cache, saved_cred);
 	if (ret < 0)
 		return ret;