fat: fix uninitialized field in nostale filehandles

[ Upstream commit fde2497d2bc3a063d8af88b258dbadc86bd7b57c ]

When fat_encode_fh_nostale() encodes file handle without a parent it
stores only first 10 bytes of the file handle. However the length of the
file handle must be a multiple of 4 so the file handle is actually 12
bytes long and the last two bytes remain uninitialized. This is not
great at we potentially leak uninitialized information with the handle
to userspace. Properly initialize the full handle length.

Link: https://lkml.kernel.org/r/20240205122626.13701-1-jack@suse.cz
Reported-by: syzbot+3ce5dea5b1539ff36769@syzkaller.appspotmail.com
Fixes: ea3983ace6b7 ("fat: restructure export_operations")
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: Amir Goldstein <amir73il@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/fs/fat/nfs.c b/fs/fat/nfs.c
index eb192656fba2787a682acefbc9c6d9bed5c1fa2c..f442a8d2f114b86d5ad6e73866f2c3e6ec14c739 100644 (file)
--- a/fs/fat/nfs.c
+++ b/fs/fat/nfs.c
@@ -139,6 +139,12 @@ fat_encode_fh_nostale(struct inode *inode, __u32 *fh, int *lenp,
                fid->parent_i_gen = parent->i_generation;
                type = FILEID_FAT_WITH_PARENT;
                *lenp = FAT_FID_SIZE_WITH_PARENT;
+       } else {
+               /*
+                * We need to initialize this field because the fh is actually
+                * 12 bytes long
+                */
+               fid->parent_i_pos_hi = 0;
        }
 
        return type;