[PATCH 4.18 061/197] fs/dcache.c: fix kmemcheck splat at take_dentry_name_snapshot()

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 6cd00a01f0c1ae6a852b09c59b8dd55cc6c35d1d ]

Since only dentry->d_name.len + 1 bytes out of DNAME_INLINE_LEN bytes
are initialized at __d_alloc(), we can't copy the whole size
unconditionally.

 WARNING: kmemcheck: Caught 32-bit read from uninitialized memory (ffff8fa27465ac50)
 636f6e66696766732e746d70000000000010000000000000020000000188ffff
  i i i i i i i i i i i i i u u u u u u u u u u i i i i i u u u u
                                  ^
 RIP: 0010:take_dentry_name_snapshot+0x28/0x50
 RSP: 0018:ffffa83000f5bdf8 EFLAGS: 00010246
 RAX: 0000000000000020 RBX: ffff8fa274b20550 RCX: 0000000000000002
 RDX: ffffa83000f5be40 RSI: ffff8fa27465ac50 RDI: ffffa83000f5be60
 RBP: ffffa83000f5bdf8 R08: ffffa83000f5be48 R09: 0000000000000001
 R10: ffff8fa27465ac00 R11: ffff8fa27465acc0 R12: ffff8fa27465ac00
 R13: ffff8fa27465acc0 R14: 0000000000000000 R15: 0000000000000000
 FS:  00007f79737ac8c0(0000) GS:ffffffff8fc30000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: ffff8fa274c0b000 CR3: 0000000134aa7002 CR4: 00000000000606f0
  take_dentry_name_snapshot+0x28/0x50
  vfs_rename+0x128/0x870
  SyS_rename+0x3b2/0x3d0
  entry_SYSCALL_64_fastpath+0x1a/0xa4
  0xffffffffffffffff

Link: http://lkml.kernel.org/r/201709131912.GBG39012.QMJLOVFSFFOOtH@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
Cc: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 fs/dcache.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -292,7 +292,8 @@ void take_dentry_name_snapshot(struct na
 		spin_unlock(&dentry->d_lock);
 		name->name = p->name;
 	} else {
-		memcpy(name->inline_name, dentry->d_iname, DNAME_INLINE_LEN);
+		memcpy(name->inline_name, dentry->d_iname,
+		       dentry->d_name.len + 1);
 		spin_unlock(&dentry->d_lock);
 		name->name = name->inline_name;
 	}