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

ksmbd: reject undersized decompressed SMB2 requests

2026-07-22T14:54:10Z

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

2026-07-22T14:54:10Z

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

2026-07-22T14:54:10Z

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

2026-07-22T14:54:10Z

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

2026-07-22T14:54:10Z

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

2026-07-22T14:54:10Z

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

2026-07-22T14:54:03Z

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

ksmbd: preserve VFS inherited POSIX ACL mask

2026-07-22T14:54:01Z

The VFS initializes a child's POSIX ACL from the parent's default ACL and the requested creation mode. Do not mutate the parent ACL or overwrite the child's VFS-computed access and default ACLs afterwards. This preserves restrictive ACL_MASK entries and prevents SMB object creation from widening effective permissions. Reported-by: Charles Vosburgh Signed-off-by: Namjae Jeon Signed-off-by: Steve French

Merge tag 'v7.2-rc3-smb3-server-fixes' of git://git.samba.org/ksmbd

2026-07-18T04:41:54Z

Pull smb server fixes from Steve French: "ksmbd server fixes, mostly addressing malformed SMB request handling and connection/session lifetime issues, including two information-disclosure or memory-safety bugs in the SMB2 request/response paths. - validate FILE_ALLOCATION_INFORMATION before block rounding to prevent a client-controlled overflow from truncating a file. - pin connections while asynchronous oplock and lease-break notifications are pending. - initialize compound SMB2 READ alignment padding, preventing disclosure of uninitialized heap bytes. - release the allocated alternate-stream xattr name after rename. - size multichannel binding session-key buffers for the largest permitted key, avoiding a stack buffer overflow. - remove a disconnecting connection's channels from every session, including channels whose binding state has since changed. - serialize binding preauthentication-session lookup and update against its teardown. - check that every compound request element contains StructureSize2 before reading it" * tag 'v7.2-rc3-smb3-server-fixes' of git://git.samba.org/ksmbd: ksmbd: validate compound request size before reading StructureSize2 ksmbd: lock the binding preauth session in smb3_preauth_hash_rsp ksmbd: remove stale channels from all sessions on teardown ksmbd: fix stack buffer overflow in multichannel session-key copy ksmbd: fix memory leak of xattr_stream_name in smb2_rename() ksmbd: zero the smb2_read alignment tail to avoid an infoleak ksmbd: pin conn during async oplock break notification ksmbd: fix integer overflow in set_file_allocation_info()

ksmbd: validate compound request size before reading StructureSize2

2026-07-16T15:18:25Z

When ksmbd validates a compound (chained) SMB2 request, ksmbd_smb2_check_message() reads pdu->StructureSize2 without first checking that the compound element is large enough to contain it. StructureSize2 is a 2-byte field at offset 64 (__SMB2_HEADER_STRUCTURE_SIZE) from the start of each element. The compound-walking logic only guarantees that a full 64-byte SMB2 header is present for the trailing element: when NextCommand is 0, len is reduced to the number of bytes remaining after next_smb2_rcv_hdr_off. A remote client can craft a compound request whose last element has exactly 64 bytes, so the 2-byte StructureSize2 read at offset 64 extends one byte past the receive buffer, producing a slab-out-of-bounds read. BUG: KASAN: slab-out-of-bounds in ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402) Read of size 2 at addr ffff888012ae31ac by task kworker/0:1/14 The buggy address is located 172 bytes inside of allocated 173-byte region Workqueue: ksmbd-io handle_ksmbd_work Call Trace: ... kasan_report (mm/kasan/report.c:595) ksmbd_smb2_check_message (fs/smb/server/smb2misc.c:402) handle_ksmbd_work (fs/smb/server/server.c:119) process_one_work (kernel/workqueue.c:3314) worker_thread (kernel/workqueue.c:3397) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) Reject any compound element that is too small to hold StructureSize2 before dereferencing it. Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3") Reported-by: AutonomousCodeSecurity@microsoft.com Signed-off-by: Xiang Mei (Microsoft) Acked-by: Namjae Jeon Signed-off-by: Steve French