From: ChenXiaoSong <chenxiaosong@chenxiaosong.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-cifs@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, Steve French <sfrench@samba.org>,
Paulo Alcantara <pc@manguebit.org>,
Ronnie Sahlberg <ronniesahlberg@gmail.com>,
Shyam Prasad N <sprasad@microsoft.com>,
Tom Talpey <tom@talpey.com>, Bharath SM <bharathsm@microsoft.com>,
samba-technical@lists.samba.org, stable <stable@kernel.org>
Subject: Re: [PATCH 1/2] smb: client: fix off-by-8 bounds check in check_wsl_eas()
Date: Wed, 8 Apr 2026 10:51:12 +0800 [thread overview]
Message-ID: <d998240c-aca9-420d-9dbd-f5ba24af19e0@chenxiaosong.com> (raw)
In-Reply-To: <2026040636-unsigned-jackal-e239@gregkh>
Sashiko reported another out-of-bounds issue:
https://sashiko.dev/#/patchset/2026040635-banking-unsoiled-3250@gregkh
Should we add the following checks in check_wsl_eas()?
```
--- a/fs/smb/client/smb2inode.c
+++ b/fs/smb/client/smb2inode.c
@@ -121,6 +121,9 @@ static int check_wsl_eas(struct kvec *rsp_iov)
ea = (void *)((u8 *)rsp_iov->iov_base +
le16_to_cpu(rsp->OutputBufferOffset));
end = (u8 *)rsp_iov->iov_base + rsp_iov->iov_len;
+ if (ea + outlen > end)
+ return -EINVAL;
+
for (;;) {
if ((u8 *)ea > end - sizeof(*ea))
return -EINVAL;
```
On 4/6/26 21:49, Greg Kroah-Hartman wrote:
> The bounds check uses (u8 *)ea + nlen + 1 + vlen as the end of the EA
> name and value, but ea_data sits at offset sizeof(struct
> smb2_file_full_ea_info) = 8 from ea, not at offset 0. The strncmp()
> later reads ea->ea_data[0..nlen-1] and the value bytes follow at
> ea_data[nlen+1..nlen+vlen], so the actual end is ea->ea_data + nlen + 1
> + vlen. Isn't pointer math fun?
>
> The earlier check (u8 *)ea > end - sizeof(*ea) only guarantees the
> 8-byte header is in bounds, but since the last EA is placed within 8
> bytes of the end of the response, the name and value bytes are read past
> the end of iov.
>
> Fix this mess all up by using ea->ea_data as the base for the bounds
> check.
>
> An "untrusted" server can use this to leak up to 8 bytes of kernel heap
> into the EA name comparison and influence which WSL xattr the data is
> interpreted as.
>
> Cc: Steve French <sfrench@samba.org>
> Cc: Paulo Alcantara <pc@manguebit.org>
> Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
> Cc: Shyam Prasad N <sprasad@microsoft.com>
> Cc: Tom Talpey <tom@talpey.com>
> Cc: Bharath SM <bharathsm@microsoft.com>
> Cc: linux-cifs@vger.kernel.org
> Cc: samba-technical@lists.samba.org
> Cc: stable <stable@kernel.org>
> Assisted-by: gregkh_clanker_t1000
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
> fs/smb/client/smb2inode.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/smb/client/smb2inode.c b/fs/smb/client/smb2inode.c
> index 364bdcff9c9d..fe1c9d776580 100644
> --- a/fs/smb/client/smb2inode.c
> +++ b/fs/smb/client/smb2inode.c
> @@ -128,7 +128,7 @@ static int check_wsl_eas(struct kvec *rsp_iov)
> nlen = ea->ea_name_length;
> vlen = le16_to_cpu(ea->ea_value_length);
> if (nlen != SMB2_WSL_XATTR_NAME_LEN ||
> - (u8 *)ea + nlen + 1 + vlen > end)
> + (u8 *)ea->ea_data + nlen + 1 + vlen > end)
> return -EINVAL;
>
> switch (vlen) {
--
ChenXiaoSong <chenxiaosong@kylinos.cn>
Chinese Homepage: chenxiaosong.com
English Homepage: chenxiaosong.com/en
next prev parent reply other threads:[~2026-04-08 2:52 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-06 13:49 [PATCH 0/2] smb: some potential bugfixes Greg Kroah-Hartman
2026-04-06 13:49 ` [PATCH 1/2] smb: client: fix off-by-8 bounds check in check_wsl_eas() Greg Kroah-Hartman
2026-04-08 2:51 ` ChenXiaoSong [this message]
2026-04-08 5:39 ` Greg Kroah-Hartman
2026-04-08 5:58 ` ChenXiaoSong
2026-04-08 6:15 ` Greg Kroah-Hartman
2026-04-08 6:19 ` ChenXiaoSong
2026-04-08 6:40 ` Greg Kroah-Hartman
2026-04-08 6:52 ` ChenXiaoSong
2026-04-08 6:56 ` Greg Kroah-Hartman
2026-04-09 3:09 ` ChenXiaoSong
2026-04-08 9:39 ` Yuanfu Xie
2026-04-06 13:49 ` [PATCH 2/2] smb: client: fix OOB reads parsing symlink error response Greg Kroah-Hartman
2026-04-08 9:01 ` ChenXiaoSong
2026-04-07 3:03 ` [PATCH 0/2] smb: some potential bugfixes Paulo Alcantara
[not found] ` <CAH2r5mvXFzWxs70Jmg=yWddmcHs+Bpf8eiBUvyc4oOMLzdCY7w@mail.gmail.com>
2026-04-08 5:45 ` Greg Kroah-Hartman
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