[PATCH v2] smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path

[Michael Bommarito <michael.bommarito@gmail.com>]

smb2_ioctl_query_info() has two response-copy branches: PASSTHRU_FSCTL
and the default QUERY_INFO path.  The QUERY_INFO branch clamps
qi.input_buffer_length to the server-reported OutputBufferLength and then
copies qi.input_buffer_length bytes from qi_rsp->Buffer to userspace, but
it never verifies that the flexible-array payload actually fits within
rsp_iov[1].iov_len.

A malicious server can return OutputBufferLength larger than the actual
QUERY_INFO response, causing copy_to_user() to walk past the response
buffer and expose adjacent kernel heap to userspace.

Guard the QUERY_INFO copy with a bounds check on the actual Buffer
payload.  Use struct_size(qi_rsp, Buffer, qi.input_buffer_length)
rather than an open-coded addition so the guard cannot overflow on
32-bit builds.

Fixes: f5778c398713 ("SMB3: Allow SMB3 FSCTL queries to be sent to server from tools")
Cc: stable@vger.kernel.org
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
---
Changes in v2:
Use struct_size() for the new QUERY_INFO bound so the guard cannot wrap
on 32-bit builds.
Keep the check anchored to qi_rsp->Buffer, since that is what the
current copy_to_user() actually reads; OutputBufferOffset would only
matter if the copy site changed too.
Also reran the synthetic 73-byte post-fix case under UML and confirmed
the new guard still rejects it cleanly.

 fs/smb/client/smb2ops.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/smb/client/smb2ops.c b/fs/smb/client/smb2ops.c
index 509fcea28a42..3600705255f8 100644
--- a/fs/smb/client/smb2ops.c
+++ b/fs/smb/client/smb2ops.c
@@ -1783,6 +1783,12 @@ smb2_ioctl_query_info(const unsigned int xid,
 		qi_rsp = (struct smb2_query_info_rsp *)rsp_iov[1].iov_base;
 		if (le32_to_cpu(qi_rsp->OutputBufferLength) < qi.input_buffer_length)
 			qi.input_buffer_length = le32_to_cpu(qi_rsp->OutputBufferLength);
+		if (qi.input_buffer_length > 0 &&
+		    struct_size(qi_rsp, Buffer, qi.input_buffer_length) >
+		    rsp_iov[1].iov_len) {
+			rc = -EFAULT;
+			goto out;
+		}
 		if (copy_to_user(&pqi->input_buffer_length,
 				 &qi.input_buffer_length,
 				 sizeof(qi.input_buffer_length))) {
-- 
2.53.0