Vegard Nossum wrote: > kmemcheck knows how to memcpy() the shadow memory state between two > slab-allocated objects, but it doesn't track memory state for the > stack so if you're copying partially uninitialised object to the stack > (which I'm guessing is the case here?) then it will produce the > warning Tetsuo Handa saw. > > BTW as soon as msan/kmsan support for the kernel [1] is merged I am > planning to nuke kmemcheck from the kernel. msan/kmsan should handle > it properly. > > [1]: https://github.com/google/kmsan I think kmemcheck is correct and msan/kmsan must as well splat here, for they won't be able to know that this unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */ field is interpreted as "only bytes up to first '\0' are valid". ---------- >From c4fe364445f7b2490209aba90b289f0543b3cfa8 Mon Sep 17 00:00:00 2001 From: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> Date: Wed, 13 Sep 2017 18:47:50 +0900 Subject: [PATCH] dentry: Fix kmemcheck splat at take_dentry_name_snapshot() 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 Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx> --- fs/dcache.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index f901413..ad6d328 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -291,7 +291,8 @@ void take_dentry_name_snapshot(struct name_snapshot *name, struct dentry *dentry 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; } -- 1.8.3.1
