6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Samuel Page <redacted>
commit 35d1ea92c7d946e2ebdbe36cdb2c969c8704bebd upstream.
ni_read_frame() decompresses an LZNT $DATA frame into the vmapped target
pages and then trusts decompress_lznt()'s return value:
unc_size = decompress_lznt(frame_ondisk, ondisk_size, frame_mem,
frame_size);
if ((ssize_t)unc_size < 0) err = unc_size;
else if (!unc_size || unc_size > frame_size) err = -EINVAL;
decompress_lznt() stops as soon as the compressed stream is exhausted
(e.g. a zero chunk header) and returns the number of bytes it actually
wrote, which may be far less than frame_size. The bytes between unc_size
and frame_size are never written. The only memset() that follows zeroes
the region beyond i_valid; when the frame lies entirely within the file's
valid size that memset() does not run, so the gap retains whatever was in
the just-vmapped pages. All pages are then marked uptodate and returned
to userspace, disclosing uninitialized (recently-freed) kernel page
memory. A crafted compressed file whose stream decompresses to only a few
bytes leaks the remainder of every frame on a plain read(2), which is
enough to recover kernel pointers and defeat KASLR.
Zero the [unc_size, frame_size) tail immediately after a successful LZNT
decompress so the remainder reads back as zero.
Fixes: 4342306f0f0d ("fs/ntfs3: Add file operations and implementation")
Cc: <redacted>
Assisted-by: Bynario AI
Signed-off-by: Samuel Page <redacted>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/ntfs3/frecord.c | 9 +++++++++
1 file changed, 9 insertions(+)
--- a/fs/ntfs3/frecord.c
+++ b/fs/ntfs3/frecord.c
@@ -2781,6 +2781,15 @@ int ni_read_frame(struct ntfs_inode *ni,
err = unc_size;
else if (!unc_size || unc_size > frame_size)
err = -EINVAL;
+ else if (unc_size < frame_size) {
+ /*
+ * Partial decompress: zero the [unc_size, frame_size)
+ * tail. decompress_lznt() leaves it untouched, so
+ * without this the freshly vmapped pages would expose
+ * uninitialized kernel memory to userspace.
+ */
+ memset(frame_mem + unc_size, 0, frame_size - unc_size);
+ }
}
if (!err && valid_size < frame_vbo + frame_size) {
size_t ok = valid_size - frame_vbo;