From 3c0da3d163eb32f1f91891efaade027fa9b245b9 Mon Sep 17 00:00:00 2001
From: Jann Horn <jannh@google.com>
Date: Tue, 6 Aug 2024 21:51:42 +0200
Subject: [PATCH] fuse: Initialize beyond-EOF page contents before setting
uptodate
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: stable@kernel.org
Fixes: a1d75f258230 ("fuse: add store request")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---
fs/fuse/dev.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index 9eb191b5c4de1..7146038b2fe7d 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);
--
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