Search Results (24075 CVEs found)

CVE Vendors Products Updated CVSS v3.1
CVE-2026-72130 1 Linux 1 Linux Kernel 2026-10-30 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: nvmet-auth: reject short AUTH_RECEIVE buffers nvmet_execute_auth_receive() trusts the AUTH_RECEIVE allocation length after checking only that it is nonzero and matches the transfer length. In the SUCCESS1 and FAILURE1/default states, that lets a remote NVMe-oF initiator reach the fixed-size DH-HMAC-CHAP response builders with a kmalloc() buffer shorter than the response, so nvmet_auth_success1() and nvmet_auth_failure1() write past the allocation; both only WARN_ON the short length and then format the message anyway. Impact: A remote NVMe-oF initiator with access to an auth-enabled target can trigger a 16-byte heap out-of-bounds write via a one-byte AUTH_RECEIVE allocation length. Compute the minimum response length for the current DH-HMAC-CHAP step in nvmet_auth_receive_data_len() and report a zero data length when the host-supplied allocation length is shorter, so the existing zero-length check in nvmet_execute_auth_receive() rejects the command before any builder runs. The SUCCESS1 minimum is sizeof(struct nvmf_auth_dhchap_success1_data) plus the HMAC hash length, because the response hash is written into the rval[] flexible-array tail, so the minimum is state dependent rather than a flat sizeof. CHALLENGE keeps its existing variable-length guard in nvmet_auth_challenge(). This is reachable only when in-band DH-HMAC-CHAP authentication is configured on the target.
CVE-2026-72098 1 Linux 1 Linux Kernel 2026-10-30 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: dm-verity: fix buffer overflow in FEC calculation There's a buffer overflow in dm-verity-fec: if (neras && *neras <= v->fec->roots) fio->erasures[(*neras)++] = i; This allows *neras to reach roots + 1 (the post-increment pushes it past roots). This value is then passed as no_eras to decode_rs8(). Inside the RS decoder (lib/reed_solomon/decode_rs.c:113-121), the erasure locator polynomial loop writes lambda[j] where j can reach nroots + 1 — one element past the end of lambda[] (which is sized nroots + 1, valid indices 0..nroots). The out-of-bounds write lands on syn[0], corrupting the syndrome buffer.
CVE-2026-72028 1 Linux 1 Linux Kernel 2026-10-30 5.5 Medium
In the Linux kernel, the following vulnerability has been resolved: riscv: probes: save original sp in rethook trampoline Reading a word from the stack in a kretprobe crashes a risc-v kernel. $ cd /sys/kernel/tracing/ $ echo 'r n_tty_write $stack0' > dynamic_events $ echo 1 > events/kprobes/enable Unable to handle kernel paging request at virtual address 0000000200000128 ... [<ffffffff80016d16>] regs_get_kernel_stack_nth+0x26/0x38 [<ffffffff80177196>] process_fetch_insn+0x3ee/0x760 [<ffffffff80177836>] kretprobe_trace_func+0x116/0x1f0 [<ffffffff8017795a>] kretprobe_dispatcher+0x4a/0x58 [<ffffffff8013572e>] kretprobe_rethook_handler+0x5e/0x90 [<ffffffff80180838>] rethook_trampoline_handler+0x70/0x108 [<ffffffff8001ba32>] arch_rethook_trampoline_callback+0x12/0x1c [<ffffffff8001ba84>] arch_rethook_trampoline+0x48/0x94 [<ffffffff8067872a>] tty_write+0x1a/0x30 In regs_get_kernel_stack_nth, regs->sp contains an arbitrary value. arch_rethook_trampoline saves the registers from the probed function in a struct pt_regs. sp is not saved. Instead, sp is decremented for arch_rethook_trampoline's local stack. Fix this crash and save the original sp along with the other registers. Use a0 as a temporary register, it is overwritten anyway. [pjw@kernel.org: added Fixes tag; cc'ed stable]
CVE-2026-68401 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: firmware: arm_ffa: Fix out-of-bound writes in ffa_setup_and_transmit() Sashiko (locally) reports multiple out-of-bound issues in ffa_setup_and_transmit: 1) Writing ep_mem_access->reserved can write out of bounds for FFA versions < 1.2 as ffa_emad_size_get() returns 16 bytes in that case while reserved has an offset of 24. Instead of zeroing fields, memset the struct to zero first based on the FFA version. 2) Make sure there is enough size to write constituents. While at it, convert the only sizeof() in the driver that uses a type instead of variable.
CVE-2026-68258 1 Linux 1 Linux Kernel 2026-10-30 7.1 High
In the Linux kernel, the following vulnerability has been resolved: drm/amdkfd: Check bounds on CRIU restore queue type and mqd size We weren't checking whether the values provided in the private data in kfd CRIU restore were within bounds. For queue type, add a KFD_QUEUE_TYPE_MAX and ensure the provided type is less than it. For mqd_size, add new function mqd_size_from_queue_type and confirm that the provided mqd_size matches expectations. (cherry picked from commit f19d8086f6644083c913d70bfdeee20e1b6f46a5)
CVE-2026-64036 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: cgroup/rstat: validate cpu before css_rstat_cpu() access css_rstat_updated() is exposed as a BPF kfunc and accepts a caller-provided cpu argument. The function uses cpu for per-cpu rstat lookups without checking whether it refers to a valid possible CPU. A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu == 0x7fffffff triggers: UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9 index 2147483647 is out of range for type 'long unsigned int [64]' Call Trace: css_rstat_updated bpf_iter_run_prog cgroup_iter_seq_show bpf_seq_read Add cpu validation to the BPF-facing css_rstat_updated() kfunc and move the common implementation to __css_rstat_updated() for in-kernel callers.
CVE-2026-63825 1 Linux 1 Linux Kernel 2026-10-30 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: gcov: use atomic counter updates to fix concurrent access crashes GCC's GCOV instrumentation can merge global branch counters with loop induction variables as an optimization. In inflate_fast(), the inner copy loops get transformed so that the GCOV counter value is loaded multiple times to compute the loop base address, start index, and end bound. Since GCOV counters are global (not per-CPU), concurrent execution on different CPUs causes the counter to change between loads, producing inconsistent values and out-of-bounds memory writes. The crash manifests during IPComp (IP Payload Compression) processing when inflate_fast() runs concurrently on multiple CPUs: BUG: unable to handle page fault for address: ffffd0a3c0902ffa RIP: inflate_fast+1431 Call Trace: zlib_inflate __deflate_decompress crypto_comp_decompress ipcomp_decompress [xfrm_ipcomp] ipcomp_input [xfrm_ipcomp] xfrm_input At the crash point, the compiler generated three loads from the same global GCOV counter (__gcov0.inflate_fast+216) to compute base, start, and end for an indexed loop. Another CPU modified the counter between loads, making the values inconsistent - the write went 3.4 MB past a 65 KB buffer. Add -fprofile-update=prefer-atomic to CFLAGS_GCOV at the global level in the top-level Makefile, guarded by a try-run compile test. The test compiles a minimal program with and without -fprofile-update=prefer-atomic using the full KBUILD_CFLAGS, then compares undefined symbols in the resulting object files. If prefer-atomic introduces new undefined references (such as __atomic_fetch_add_8 on i386 or __aarch64_ldadd8_relax on arm64 with outline-atomics), the flag is not added -- the kernel does not link against libatomic. On architectures where GCC inlines 64-bit atomic counter updates (x86_64, s390, ...) the test passes and the flag is enabled, preventing the compiler from merging counters with loop induction variables and fixing the observed concurrent-access crash. On architectures where the flag would introduce libatomic dependencies, it is silently omitted and behaviour is no worse than before this patch. Move the CFLAGS_GCOV block from its original position (before the arch Makefile include) to after the core KBUILD_CFLAGS assignments but before the scripts/Makefile.gcc-plugins include. This placement ensures the try-run test sees arch-specific flags (-m32, -march=, -mno-outline-atomics) while avoiding GCC plugin flags (-fplugin=) that would break the test on clean builds when plugin shared objects do not yet exist.
CVE-2026-53267 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: netfilter: nft_ct: bail out on template ct in get eval I noticed this issue while looking at a historic syzbot report [1]. A rule like the one below is enough to trigger the bug: table ip t { chain pre { type filter hook prerouting priority raw; ct zone set 1 ct original saddr 1.2.3.4 accept } } The first expression attaches a per-cpu template ct via nft_ct_set_zone_eval() (nf_ct_tmpl_alloc -> kzalloc, tuple is all zero, nf_ct_l3num(ct) == 0). The next expression then calls nft_ct_get_eval() on the same skb, treats the template as a real ct and hits the 16-byte memcpy path. With dreg at NFT_REG32_15 this overflows past struct nft_regs on the kernel stack; with smaller dreg values it silently clobbers adjacent registers. Reject template ct at the eval entry and in nft_ct_get_fast_eval(), mirroring the check nft_ct_set_eval() already has. Additionally, bound the address copy in NFT_CT_SRC / NFT_CT_DST by priv->len instead of by nf_ct_l3num(ct): nf_ct_get_tuple() zeroes the tuple before pkt_to_tuple() fills in only the protocol-relevant leading bytes, so the trailing bytes of tuple->{src,dst}.u3.all are well-defined zero. priv->len is validated at rule load, so the copy size is now bounded by the destination register rather than by an untrusted field on the conntrack. [1]: https://syzkaller.appspot.com/bug?id=389cf09cb72926114fce90dc85a2c3231dcb647c
CVE-2026-53230 1 Linux 1 Linux Kernel 2026-10-30 8.7 High
In the Linux kernel, the following vulnerability has been resolved: net/mlx5: Fix slab-out-of-bounds in mlx5_query_nic_vport_mac_list mlx5_query_nic_vport_mac_list() sizes its firmware command buffer using the PF's log_max_current_uc/mc_list capabilities. When querying a VF vport with a larger configured max (via devlink), the firmware response can overflow this buffer: BUG: KASAN: slab-out-of-bounds in mlx5_query_nic_vport_mac_list+0x453/0x4c0 [mlx5_core] Read of size 4 at addr ff1100013ffc8a12 by task kworker/u96:2/385 CPU: 12 UID: 0 PID: 385 Comm: kworker/u96:2 Not tainted 7.0.0-rc6+ #1 PREEMPT Hardware name: QEMU Standard PC (Q35 + ICH9, 2009) Workqueue: mlx5_esw_wq esw_vport_change_handler [mlx5_core] Call Trace: <TASK> dump_stack_lvl+0x69/0xa0 print_report+0x176/0x4e4 kasan_report+0xc8/0x100 mlx5_query_nic_vport_mac_list+0x453/0x4c0 [mlx5_core] esw_update_vport_addr_list+0x2e3/0xda0 [mlx5_core] esw_vport_change_handle_locked+0xa1f/0x1060 [mlx5_core] esw_vport_change_handler+0x6a/0x90 [mlx5_core] process_one_work+0x87f/0x15e0 worker_thread+0x62b/0x1020 kthread+0x375/0x490 ret_from_fork+0x4dc/0x810 ret_from_fork_asm+0x11/0x20 </TASK> Fix by querying the vport's own HCA caps to size the buffer correctly. Refactor the function to allocate and return the MAC list internally, removing the caller's dependency on knowing the correct max.
CVE-2026-43490 1 Linux 1 Linux Kernel 2026-10-30 8.8 High
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate inherited ACE SID length smb_inherit_dacl() walks the parent directory DACL loaded from the security descriptor xattr. It verifies that each ACE contains the fixed SID header before using it, but does not verify that the variable-length SID described by sid.num_subauth is fully contained in the ACE. A malformed inheritable ACE can advertise more subauthorities than are present in the ACE. compare_sids() may then read past the ACE. smb_set_ace() also clamps the copied destination SID, but used the unchecked source SID count to compute the inherited ACE size. That could advance the temporary inherited ACE buffer pointer and nt_size accounting past the allocated buffer. Fix this by validating the parent ACE SID count and SID length before using the SID during inheritance. Compute the inherited ACE size from the copied SID so the size matches the bounded destination SID. Reject the inherited DACL if size accumulation would overflow smb_acl.size or the security descriptor allocation size.
CVE-2026-43258 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: alpha: fix user-space corruption during memory compaction Alpha systems can suffer sporadic user-space crashes and heap corruption when memory compaction is enabled. Symptoms include SIGSEGV, glibc allocator failures (e.g. "unaligned tcache chunk"), and compiler internal errors. The failures disappear when compaction is disabled or when using global TLB invalidation. The root cause is insufficient TLB shootdown during page migration. Alpha relies on ASN-based MM context rollover for instruction cache coherency, but this alone is not sufficient to prevent stale data or instruction translations from surviving migration. Fix this by introducing a migration-specific helper that combines: - MM context invalidation (ASN rollover), - immediate per-CPU TLB invalidation (TBI), - synchronous cross-CPU shootdown when required. The helper is used only by migration/compaction paths to avoid changing global TLB semantics. Additionally, update flush_tlb_other(), pte_clear(), to use READ_ONCE()/WRITE_ONCE() for correct SMP memory ordering. This fixes observed crashes on both UP and SMP Alpha systems.
CVE-2026-43250 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: usb: chipidea: udc: fix DMA and SG cleanup in _ep_nuke() The ChipIdea UDC driver can encounter "not page aligned sg buffer" errors when a USB device is reconnected after being disconnected during an active transfer. This occurs because _ep_nuke() returns requests to the gadget layer without properly unmapping DMA buffers or cleaning up scatter-gather bounce buffers. Root cause: When a disconnect happens during a multi-segment DMA transfer, the request's num_mapped_sgs field and sgt.sgl pointer remain set with stale values. The request is returned to the gadget driver with status -ESHUTDOWN but still has active DMA state. If the gadget driver reuses this request on reconnect without reinitializing it, the stale DMA state causes _hardware_enqueue() to skip DMA mapping (seeing non-zero num_mapped_sgs) and attempt to use freed/invalid DMA addresses, leading to alignment errors and potential memory corruption. The normal completion path via _hardware_dequeue() properly calls usb_gadget_unmap_request_by_dev() and sglist_do_debounce() before returning the request. The _ep_nuke() path must do the same cleanup to ensure requests are returned in a clean, reusable state. Fix: Add DMA unmapping and bounce buffer cleanup to _ep_nuke() to mirror the cleanup sequence in _hardware_dequeue(): - Call usb_gadget_unmap_request_by_dev() if num_mapped_sgs is set - Call sglist_do_debounce() with copy=false if bounce buffer exists This ensures that when requests are returned due to endpoint shutdown, they don't retain stale DMA mappings. The 'false' parameter to sglist_do_debounce() prevents copying data back (appropriate for shutdown path where transfer was aborted).
CVE-2026-43248 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: vhost: move vdpa group bound check to vhost_vdpa Remove duplication by consolidating these here. This reduces the posibility of a parent driver missing them. While we're at it, fix a bug in vdpa_sim where a valid ASID can be assigned to a group equal to ngroups, causing an out of bound write.
CVE-2026-43125 1 Linux 1 Linux Kernel 2026-10-30 9.8 Critical
In the Linux kernel, the following vulnerability has been resolved: dlm: validate length in dlm_search_rsb_tree The len parameter in dlm_dump_rsb_name() is not validated and comes from network messages. When it exceeds DLM_RESNAME_MAXLEN, it can cause out-of-bounds write in dlm_search_rsb_tree(). Add length validation to prevent potential buffer overflow.
CVE-2026-43091 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: xfrm: Wait for RCU readers during policy netns exit xfrm_policy_fini() frees the policy_bydst hash tables after flushing the policy work items and deleting all policies, but it does not wait for concurrent RCU readers to leave their read-side critical sections first. The policy_bydst tables are published via rcu_assign_pointer() and are looked up through rcu_dereference_check(), so netns teardown must also wait for an RCU grace period before freeing the table memory. Fix this by adding synchronize_rcu() before freeing the policy hash tables.
CVE-2026-43048 1 Linux 1 Linux Kernel 2026-10-30 8.8 High
In the Linux kernel, the following vulnerability has been resolved: HID: core: Mitigate potential OOB by removing bogus memset() The memset() in hid_report_raw_event() has the good intention of clearing out bogus data by zeroing the area from the end of the incoming data string to the assumed end of the buffer. However, as we have previously seen, doing so can easily result in OOB reads and writes in the subsequent thread of execution. The current suggestion from one of the HID maintainers is to remove the memset() and simply return if the incoming event buffer size is not large enough to fill the associated report. Suggested-by Benjamin Tissoires <bentiss@kernel.org> [bentiss: changed the return value]
CVE-2026-31707 1 Linux 1 Linux Kernel 2026-10-30 7.1 High
In the Linux kernel, the following vulnerability has been resolved: ksmbd: validate response sizes in ipc_validate_msg() ipc_validate_msg() computes the expected message size for each response type by adding (or multiplying) attacker-controlled fields from the daemon response to a fixed struct size in unsigned int arithmetic. Three cases can overflow: KSMBD_EVENT_RPC_REQUEST: msg_sz = sizeof(struct ksmbd_rpc_command) + resp->payload_sz; KSMBD_EVENT_SHARE_CONFIG_REQUEST: msg_sz = sizeof(struct ksmbd_share_config_response) + resp->payload_sz; KSMBD_EVENT_LOGIN_REQUEST_EXT: msg_sz = sizeof(struct ksmbd_login_response_ext) + resp->ngroups * sizeof(gid_t); resp->payload_sz is __u32 and resp->ngroups is __s32. Each addition can wrap in unsigned int; the multiplication by sizeof(gid_t) mixes signed and size_t, so a negative ngroups is converted to SIZE_MAX before the multiply. A wrapped value of msg_sz that happens to equal entry->msg_sz bypasses the size check on the next line, and downstream consumers (smb2pdu.c:6742 memcpy using rpc_resp->payload_sz, kmemdup in ksmbd_alloc_user using resp_ext->ngroups) then trust the unverified length. Use check_add_overflow() on the RPC_REQUEST and SHARE_CONFIG_REQUEST paths to detect integer overflow without constraining functional payload size; userspace ksmbd-tools grows NDR responses in 4096-byte chunks for calls like NetShareEnumAll, so a hard transport cap is unworkable on the response side. For LOGIN_REQUEST_EXT, reject resp->ngroups outside the signed [0, NGROUPS_MAX] range up front and report the error from ipc_validate_msg() so it fires at the IPC boundary; with that bound the subsequent multiplication and addition stay well below UINT_MAX. The now-redundant ngroups check and pr_err in ksmbd_alloc_user() are removed. This is the response-side analogue of aab98e2dbd64 ("ksmbd: fix integer overflows on 32 bit systems"), which hardened the request side.
CVE-2026-31675 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_netem: fix out-of-bounds access in packet corruption In netem_enqueue(), the packet corruption logic uses get_random_u32_below(skb_headlen(skb)) to select an index for modifying skb->data. When an AF_PACKET TX_RING sends fully non-linear packets over an IPIP tunnel, skb_headlen(skb) evaluates to 0. Passing 0 to get_random_u32_below() takes the variable-ceil slow path which returns an unconstrained 32-bit random integer. Using this unconstrained value as an offset into skb->data results in an out-of-bounds memory access. Fix this by verifying skb_headlen(skb) is non-zero before attempting to corrupt the linear data area. Fully non-linear packets will silently bypass the corruption logic.
CVE-2026-31505 1 Linux 1 Linux Kernel 2026-10-30 7.8 High
In the Linux kernel, the following vulnerability has been resolved: iavf: fix out-of-bounds writes in iavf_get_ethtool_stats() iavf incorrectly uses real_num_tx_queues for ETH_SS_STATS. Since the value could change in runtime, we should use num_tx_queues instead. Moreover iavf_get_ethtool_stats() uses num_active_queues while iavf_get_sset_count() and iavf_get_stat_strings() use real_num_tx_queues, which triggers out-of-bounds writes when we do "ethtool -L" and "ethtool -S" simultaneously [1]. For example when we change channels from 1 to 8, Thread 3 could be scheduled before Thread 2, and out-of-bounds writes could be triggered in Thread 3: Thread 1 (ethtool -L) Thread 2 (work) Thread 3 (ethtool -S) iavf_set_channels() ... iavf_alloc_queues() -> num_active_queues = 8 iavf_schedule_finish_config() iavf_get_sset_count() real_num_tx_queues: 1 -> buffer for 1 queue iavf_get_ethtool_stats() num_active_queues: 8 -> out-of-bounds! iavf_finish_config() -> real_num_tx_queues = 8 Use immutable num_tx_queues in all related functions to avoid the issue. [1] BUG: KASAN: vmalloc-out-of-bounds in iavf_add_one_ethtool_stat+0x200/0x270 Write of size 8 at addr ffffc900031c9080 by task ethtool/5800 CPU: 1 UID: 0 PID: 5800 Comm: ethtool Not tainted 6.19.0-enjuk-08403-g8137e3db7f1c #241 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 Call Trace: <TASK> dump_stack_lvl+0x6f/0xb0 print_report+0x170/0x4f3 kasan_report+0xe1/0x180 iavf_add_one_ethtool_stat+0x200/0x270 iavf_get_ethtool_stats+0x14c/0x2e0 __dev_ethtool+0x3d0c/0x5830 dev_ethtool+0x12d/0x270 dev_ioctl+0x53c/0xe30 sock_do_ioctl+0x1a9/0x270 sock_ioctl+0x3d4/0x5e0 __x64_sys_ioctl+0x137/0x1c0 do_syscall_64+0xf3/0x690 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f7da0e6e36d ... </TASK> The buggy address belongs to a 1-page vmalloc region starting at 0xffffc900031c9000 allocated at __dev_ethtool+0x3cc9/0x5830 The buggy address belongs to the physical page: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88813a013de0 pfn:0x13a013 flags: 0x200000000000000(node=0|zone=2) raw: 0200000000000000 0000000000000000 dead000000000122 0000000000000000 raw: ffff88813a013de0 0000000000000000 00000001ffffffff 0000000000000000 page dumped because: kasan: bad access detected Memory state around the buggy address: ffffc900031c8f80: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900031c9000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 >ffffc900031c9080: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ^ ffffc900031c9100: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 ffffc900031c9180: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8
CVE-2026-31432 1 Linux 1 Linux Kernel 2026-10-30 8.8 High
In the Linux kernel, the following vulnerability has been resolved: ksmbd: fix OOB write in QUERY_INFO for compound requests When a compound request such as READ + QUERY_INFO(Security) is received, and the first command (READ) consumes most of the response buffer, ksmbd could write beyond the allocated buffer while building a security descriptor. The root cause was that smb2_get_info_sec() checked buffer space using ppntsd_size from xattr, while build_sec_desc() often synthesized a significantly larger descriptor from POSIX ACLs. This patch introduces smb_acl_sec_desc_scratch_len() to accurately compute the final descriptor size beforehand, performs proper buffer checking with smb2_calc_max_out_buf_len(), and uses exact-sized allocation + iov pinning.