Re: [PATCH 1/2] smb: client: fix off-by-8 bounds check in check_wsl_eas()

ChenXiaoSong
2026-04-08T02:52:15Z

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>
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