linux-stable.git/fs/smb/server, branch master

ksmbd: use memcmp() to compare ClientGUIDs

2026-07-30T23:45:57+00:00

ClientGUID is a fixed-size binary value and can contain embedded NUL
bytes. strncmp() stops comparing at the first NUL byte, so different
ClientGUID values can incorrectly be treated as equal.

Use memcmp() in SMB3 multichannel session binding and
FSCTL_VALIDATE_NEGOTIATE_INFO to compare all SMB2_CLIENT_GUID_SIZE
bytes.

Fixes: f5a544e3bab7 ("ksmbd: add support for SMB3 multichannel")
Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Reported-by: Samu 
Suggested-by: Samu 
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: reject repeated SMB2 NEGOTIATE requests

2026-07-30T23:45:57+00:00

Unauthenticated client can send multiple successful SMB2 NEGOTIATE
requests on one connection before SESSION_SETUP. While the connection is
in KSMBD_SESS_NEED_SETUP, smb2_handle_negotiate() accepts another
SMB3.1.1 NEGOTIATE and overwrites conn->preauth_info with a new allocation.
Only the final allocation is freed when the connection is released, leaking
one object for every additional successful request.

A repeated SMB2 NEGOTIATE after a dialect has been selected is a protocol
violation. MS-SMB2 section 3.3.5.4 requires the server to disconnect
without replying in this case. Set the connection exiting when rejecting
the request, in addition to suppressing the response.

Reject SMB2 NEGOTIATE unless the connection is new or is waiting for the
SMB2 NEGOTIATE that follows an SMB1 multi-protocol negotiate. Serialize
both SMB1 and SMB2 negotiation paths under conn->srv_mutex, since they
update connection-wide dialect and negotiation state.

Move the locking contract to ksmbd_smb_negotiate_common(), where the state
and dialect are selected, and add ksmbd_conn_new() for consistent state
access.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Reported-by: Runa Takemoto 
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: fix use-after-free in __close_file_table_ids()

2026-07-30T23:45:57+00:00

A ksmbd_file can remain alive after logical close while another session
holds a temporary reference obtained through ksmbd_lookup_fd_inode().
ksmbd_close_fd() currently marks the file closed and drops the idr-owned
reference, but leaves the pointer published in the closing session's idr
until the final reference is dropped.

If the foreign holder performs the final ksmbd_fd_put(), __put_fd_final()
supplies the foreign session's file table to __ksmbd_close_fd(). The object
is then freed without being removed from its owner's idr, and the owner
session later dereferences the stale pointer during file-table teardown.

Remove the volatile id from the owner's idr while ksmbd_close_fd() still
holds that table's lock, and clear volatile_id before dropping
the idr-owned reference. A later foreign final put then only performs
physical destruction and cannot remove the object from the wrong table.

Fixes: 8510a043d334 ("ksmbd: increment reference count of parent fp")
Reported-by: Yunseong Kim 
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: reject undersized decompressed SMB2 requests

2026-07-22T14:54:10+00:00

ksmbd_decompress_request() bounds the decompressed size only against
the maximum request size. A compression transform can therefore
produce a buffer smaller than an SMB2 PDU and install it as
conn->request_buf.

The receive path subsequently calls ksmbd_smb_request(), which reads
the protocol ID before the normal SMB2 minimum-size check. If the
decompressed output is too short, that read can access beyond the
request allocation.

Require the decompressed output to contain at least a complete minimum
SMB2 PDU before allocating and installing the replacement request
buffer.

Fixes: a08de24c2b85 ("ksmbd: negotiate and decode SMB2 compression")
Cc: stable@vger.kernel.org
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: validate minimum PDU size for transform requests

2026-07-22T14:54:10+00:00

The receive path applies the minimum SMB2 PDU size check only when
ProtocolId is SMB2_PROTO_NUMBER. A packet carrying
SMB2_TRANSFORM_PROTO_NUM bypasses the check even when the negotiated
dialect does not provide transform handling.

On an SMB 2.1 connection, a short transform packet therefore reaches
init_smb2_rsp_hdr(), which interprets the request as a full SMB2 header
and reads beyond the request allocation. The copied fields can then be
returned to the unauthenticated client.

Compression transforms are converted to ordinary SMB2 messages before
protocol validation. After that conversion, validate ordinary SMB2
requests against SMB2_MIN_SUPPORTED_PDU_SIZE and require encryption
transform requests to contain both a transform header and an SMB2
header. This rejects truncated requests before work allocation.

Fixes: 368ba06881c3 ("ksmbd: check the validation of pdu_size in ksmbd_conn_handler_loop")
Cc: stable@vger.kernel.org
Reported-by: zdi-disclosures@trendmicro.com # ZDI-CAN-31063
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: defer destroy_previous_session() until after NTLM authentication

2026-07-22T14:54:10+00:00

In ntlm_authenticate(), destroy_previous_session() is called using a
user pointer resolved from the client-supplied NTLM blob username field
before the NTLMv2 response is validated. An authenticated attacker can
set the NTLM blob username to match a victim account and set
PreviousSessionId to the victim's session ID; destroy_previous_session()
destroys the victim's session while ksmbd_decode_ntlmssp_auth_blob()
subsequently rejects the request with -EPERM.

Move destroy_previous_session() and the prev_id assignment to after
ksmbd_decode_ntlmssp_auth_blob() returns success and use sess->user
rather than the pre-authentication lookup result. This matches the
ordering already used by krb5_authenticate(), where
destroy_previous_session() is called only after
ksmbd_krb5_authenticate() returns success.

Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/linux-cifs/20260702155449.3639773-1-james_montgomery@disroot.org/
Signed-off-by: James Montgomery 
Acked-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: validate ACE size against SID sub-authorities

2026-07-22T14:54:10+00:00

set_ntacl_dacl() validates sid.num_subauth before copying an ACE, but
does not verify that the declared ACE size contains all sub-authorities
described by that field. An undersized ACE can therefore be copied
and later make the POSIX ACL deduplication walk inspect data beyond
the copied ACE boundary.

The existing initial bound check is also too small. It only ensures
that the ACE size field is accessible before set_ntacl_dacl() reads
sid.num_subauth farther into the input buffer.

Require enough input for the fixed SID header before accessing
num_subauth, reject ACEs smaller than that header, and skip ACEs
whose declared size cannot contain the complete SID. This makes the
validation consistent with the other ACE walk paths.

Reported-by: LocalHost 
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: restore DACL size on check_add_overflow() to avoid malformed ACL

2026-07-22T14:54:10+00:00

check_add_overflow() unconditionally writes the truncated sum into *d
even on overflow, per its contract in include/linux/overflow.h.
The four check_add_overflow() guards in set_posix_acl_entries_dacl()
and set_ntacl_dacl() break out of the ACE-building loops on overflow,
but the truncated *size is then consumed downstream at the end of
set_ntacl_dacl():

    pndacl->size = cpu_to_le16(le16_to_cpu(pndacl->size) + size);

This produces an on-wire NT ACL whose pndacl->size under-reports the
bytes actually written by the preceding fill_ace_for_sid()/memcpy()
calls, yielding a malformed ACL that can trigger out-of-bounds reads
when re-parsed by clients or ksmbd itself.

Restore *size to its pre-addition value on each overflow branch (via
`*size -= ace_sz` / `size -= nt_ace_size`) so that after the break,
*size once again holds the cumulative size of the successfully-written
ACEs. The committed ACL is then truncated-but-self-consistent rather
than malformed.

The ksmbd DACL builders are the only check_add_overflow() sites found
where an overflow path breaks out of a loop and the destination value
is consumed afterward. The other nearby break-style cases either
return -EINVAL on overflow (transport_ipc.c) or break without
consuming the overflowed destination value afterward (buildid.c).

Fixes: 299f962c0b02 ("ksmbd: use check_add_overflow() to prevent u16 DACL size overflow")
Assisted-by: atomcode:glm-5.2
Assisted-by: Codex:gpt-5.5
Cc: stable@vger.kernel.org
Signed-off-by: Wentao Guan 
Acked-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: bound DACL dedup walk to copied ACEs

2026-07-22T14:54:10+00:00

set_ntacl_dacl() can stop copying ACEs before consuming the full input
DACL when size accounting overflows.

When that happens, num_aces reflects only the ACEs that were actually
copied into the output DACL, but set_posix_acl_entries_dacl() still
receives nt_num_aces and uses it to walk the existing ACE array during
dedup.

That makes the dedup walk scan past the copied ACE array and inspect
buffer tail that does not contain valid ACEs.

Split the two meanings currently carried by the NT ACE count. Pass the
number of copied NT ACEs to bound the dedup walk, and preserve the
original "input DACL had NT ACEs" state separately for the
Everyone/default ACL fallback.

This keeps the dedup walk aligned with the ACEs that are actually
present in the rebuilt DACL.

Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French

ksmbd: enforce signing required by the session

2026-07-22T14:54:03+00:00

SMB2_FLAGS_SIGNED is controlled by the incoming request and only indicates
that a signature accompanies that request. Do not use it to decide whether a
signing-required session must authenticate the request.

Reject an unsigned plaintext request before dispatch when the session
requires signing. Continue to validate signatures on signed requests,
including when signing is optional. Encrypted requests have already been
authenticated during decryption.

An OPLOCK_BREAK acknowledgment is a session request and is subject to the
same signing rule, so do not exclude it from signed-request detection.

Reported-by: Charles Vosburgh 
Tested-by: ChenXiaoSong 
Reviewed-by: ChenXiaoSong 
Signed-off-by: Namjae Jeon 
Signed-off-by: Steve French