unimore/kernel-hacking-2024-linux-steffo
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fuse: Initialize beyond-EOF page contents before setting uptodate

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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: a1d75f2582 ("fuse: add store request")
Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Jann Horn 2024-08-06 21:51:42 +02:00 committed by Linus Torvalds
parent c3f2d783a4
commit 3c0da3d163
1 changed files with 4 additions and 2 deletions
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6
fs/fuse/dev.c
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@ -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);