Issue

• NFS3 クライアントが、以下のコールチェイン内で readdir 応答を処理する際にクラッシュします。nfs_readdir_page_filler -> nfs3_decode_dirent -> xdr_inline_decode -> memcpy

BUG: unable to handle kernel NULL pointer dereference at (null)

• クラッシュにより、vmcore と以下のバックトレースが作成されました。

RIP:0010:[<ffffffff812830cb>]  [<ffffffff812830cb>] memcpy+0xb/0x120
RSP:0018:ffff883d57e9bad0  EFLAGS:00010246
RAX: ffff880497efc000 RBX: ffff883d57e9bc08 RCX:000000000afd37a1
RDX:0000000000000000 RSI:0000000000000000 RDI: ffff880497efc000
RBP: ffff883d57e9baf8 R08:0000000000000000 R09:0000000000000000
R10:0000000000000000 R11:0000000000000400 R12:0000000000000004
R13: ffff880497efc000 R14: ffff883d57e9bd08 R15: ffff881064f7d780
FS:00007f6b174507a0(0000) GS:ffff880028360000(0000) knlGS:0000000000000000
CS:0010 DS:0000 ES:0000 CR0:000000008005003b
CR2:0000000000000000 CR3:0000001e3025e000 CR4:00000000000407e0
DR0:0000000000000000 DR1:0000000000000000 DR2:0000000000000000
DR3:0000000000000000 DR6:00000000ffff0ff0 DR7:0000000000000400
Process ls (pid:49211, threadinfo ffff883d57e9a000, task ffff883511c26aa0)
Stack:
 ffffffffa047aa71 ffff883d57e9bcc8 ffff883d57e9bc08 000000009d1deb58
<d> ffff88102da79080 ffff883d57e9bb78 ffffffffa04f8aa6 ffff88000001aec0
<d> ffffffffa046f0b0 0000001057e9bce8 0000000000000000 0000000000000000
Call Trace:
 [<ffffffffa047aa71>] ? xdr_inline_decode+0xb1/0x120 [sunrpc]
 [<ffffffffa04f8aa6>] nfs3_decode_dirent+0x66/0x3d0 [nfs]
 [<ffffffffa046f0b0>] ? rpc_do_put_task+0x30/0x40 [sunrpc]
 [<ffffffffa04df26a>] nfs_readdir_page_filler+0x11a/0x580 [nfs]
 [<ffffffffa04df8d8>] nfs_readdir_xdr_to_array+0x208/0x2b0 [nfs]
 [<ffffffffa04df9a6>] nfs_readdir_filler+0x26/0xa0 [nfs]
 [<ffffffff8111a33e>] ? add_to_page_cache_lru+0x3e/0x50
 [<ffffffff8111bd2b>] do_read_cache_page+0x7b/0x180
 [<ffffffffa04df980>] ? nfs_readdir_filler+0x0/0xa0 [nfs]
 [<ffffffff811961e0>] ? filldir+0x0/0xe0
 [<ffffffff8111be79>] read_cache_page_async+0x19/0x20
 [<ffffffff8111be8e>] read_cache_page+0xe/0x20
 [<ffffffffa04dfb92>] nfs_readdir+0x172/0x5f0 [nfs]
 [<ffffffffa04f8a40>] ? nfs3_decode_dirent+0x0/0x3d0 [nfs]
 [<ffffffff811961e0>] ? filldir+0x0/0xe0
 [<ffffffff81196460>] vfs_readdir+0xc0/0xe0
 [<ffffffff811965e9>] sys_getdents+0x89/0xf0
 [<ffffffff8100b072>] system_call_fastpath+0x16/0x1b
Code:49 89 70 50 19 c0 49 89 70 58 41 c6 40 4c 04 83 e0 fc 83 c0 08 41 88 40 4d c9 c3 90 90 90 90 90 48 89 f8 89 d1 c1 e9 03 83 e2 07 <f3> 48 a5 89 d1 f3 a4 c3 20 48 83 ea 20 4c 8b 06 4c 8b 4e 08 4c 
RIP  [<ffffffff812830cb>] memcpy+0xb/0x120
 RSP <ffff883d57e9bad0>
CR2:0000000000000000