[PATCH AUTOSEL 6.18-5.15] ksmbd: fix credit charge calculation for SMB2 QUERY_INFO

[Sasha Levin <sashal@kernel.org>]

From: Namjae Jeon <linkinjeon@kernel.org>

[ Upstream commit 284dc80ff529a0b454f11b6c2fea0d5daf6f315f ]

smb2_validate_credit_charge() computes the credit charge a request is
allowed to consume from the payload size:

  CreditCharge = (max(SendPayloadSize, ResponsePayloadSize) - 1)/65536 + 1

For SMB2 QUERY_INFO, the server must validate CreditCharge based on the
*maximum* of InputBufferLength and OutputBufferLength. ksmbd instead
summed the two lengths, which overestimates the required charge.

As a result a single-credit QUERY_INFO whose InputBufferLength and
OutputBufferLength each fit in 64KB but whose sum exceeds 64KB is
rejected with STATUS_INVALID_PARAMETER, even though it is a valid
request. IOCTL already uses max() of the request and response sizes;
make QUERY_INFO consistent by feeding InputBufferLength as the request
length and OutputBufferLength as the expected response length so that
smb2_validate_credit_charge() takes their maximum.

Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

The `git log -S "smb2_query_info_resp_len"` search finished with no
results — that helper from the fix commit isn’t in this tree’s history,
which confirms the patch hasn’t landed on this branch yet. That’s
consistent with the earlier **YES** backport recommendation for 6.18.44.

 fs/smb/server/smb2misc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/smb/server/smb2misc.c b/fs/smb/server/smb2misc.c
index d8913d2008748..efbbf7ea48094 100644
--- a/fs/smb/server/smb2misc.c
+++ b/fs/smb/server/smb2misc.c
@@ -262,8 +262,12 @@ static int smb2_calc_size(void *buf, unsigned int *len)
 
 static inline int smb2_query_info_req_len(struct smb2_query_info_req *h)
 {
-	return le32_to_cpu(h->InputBufferLength) +
-		le32_to_cpu(h->OutputBufferLength);
+	return le32_to_cpu(h->InputBufferLength);
+}
+
+static inline int smb2_query_info_resp_len(struct smb2_query_info_req *h)
+{
+	return le32_to_cpu(h->OutputBufferLength);
 }
 
 static inline int smb2_set_info_req_len(struct smb2_set_info_req *h)
@@ -310,6 +314,7 @@ static int smb2_validate_credit_charge(struct ksmbd_work *work,
 	switch (hdr->Command) {
 	case SMB2_QUERY_INFO:
 		req_len = smb2_query_info_req_len(__hdr);
+		expect_resp_len = smb2_query_info_resp_len(__hdr);
 		break;
 	case SMB2_SET_INFO:
 		req_len = smb2_set_info_req_len(__hdr);
-- 
2.53.0