fuse: Initialize beyond-EOF page contents before setting uptodate

3c0da3d1 · Jann Horn <[email protected]> · 2024-08-06 21:51:42 +02:00

fuse_notify_store(), unlike fuse_do_readpage(), does not enable page
zeroing (because it can be used to change partial page contents).

So fuse_notify_store() must be more careful to fully initialize page
contents (including parts of the page that are beyond end-of-file)
before marking the page uptodate.

The current code can leave beyond-EOF page contents uninitialized, which
makes these uninitialized page contents visible to userspace via mmap().

This is an information leak, but only affects systems which do not
enable init-on-alloc (via CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y or the
corresponding kernel command line parameter).

Link: https://bugs.chromium.org/p/project-zero/issues/detail?id=2574
Cc: [email protected]
Fixes: a1d75f258230 ("fuse: add store request")
Signed-off-by: Jann Horn <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 3c0da3d163eb32f1f91891efaade027fa9b245b9
Parents: c3f2d783

Changes

1 files changed · +4 −2

File	Status	Add	Del	Content
fs/fuse/dev.c	modified	+4	−2	View file

fs/fuse/dev.c

View file

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 9eb191b..7146038 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -1618,9 +1618,11 @@ static int fuse_notify_store(struct fuse_conn *fc, unsigned int size,
 
 		this_num = min_t(unsigned, num, PAGE_SIZE - offset);
 		err = fuse_copy_page(cs, &page, offset, this_num, 0);
-		if (!err && offset == 0 &&
-		    (this_num == PAGE_SIZE || file_size == end))
+		if (!PageUptodate(page) && !err && offset == 0 &&
+		    (this_num == PAGE_SIZE || file_size == end)) {
+			zero_user_segment(page, this_num, PAGE_SIZE);
 			SetPageUptodate(page);
+		}
 		unlock_page(page);
 		put_page(page);
 