Linux: >> Linux Kernel >> 5.15.106 Security Vulnerabilities
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: require minimum ACE size in smb_check_perm_dacl()
Both ACE-walk loops in smb_check_perm_dacl() only guard against an
under-sized remaining buffer, not against an ACE whose declared
`ace->size` is smaller than the struct it claims to describe:
if (offsetof(struct smb_ace, access_req) > aces_size)
break;
ace_size = le16_to_cpu(ace->size);
if (ace_size > aces_size)
break;
The first check only requires the 4-byte ACE header to be in bounds;
it does not require access_req (4 bytes at offset 4) to be readable.
An attacker who has set a crafted DACL on a file they own can declare
ace->size == 4 with aces_size == 4, pass both checks, and then
granted |= le32_to_cpu(ace->access_req); /* upper loop */
compare_sids(&sid, &ace->sid); /* lower loop */
reads access_req at offset 4 (OOB by up to 4 bytes) and ace->sid at
offset 8 (OOB by up to CIFS_SID_BASE_SIZE + SID_MAX_SUB_AUTHORITIES
* 4 bytes).
Tighten both loops to require
ace_size >= offsetof(struct smb_ace, sid) + CIFS_SID_BASE_SIZE
which is the smallest valid on-wire ACE layout (4-byte header +
4-byte access_req + 8-byte sid base with zero sub-auths). Also
reject ACEs whose sid.num_subauth exceeds SID_MAX_SUB_AUTHORITIES
before letting compare_sids() dereference sub_auth[] entries.
parse_sec_desc() already enforces an equivalent check (lines 441-448);
smb_check_perm_dacl() simply grew weaker validation over time.
Reachability: authenticated SMB client with permission to set an ACL
on a file. On a subsequent CREATE against that file, the kernel
walks the stored DACL via smb_check_perm_dacl() and triggers the
OOB read. Not pre-auth, and the OOB read is not reflected to the
attacker, but KASAN reports and kernel state corruption are
possible.
CVSS Score
8.3
EPSS Score
0.003
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix UAF caused by decrementing sbi->nr_pages[] in f2fs_write_end_io()
The xfstests case "generic/107" and syzbot have both reported a NULL
pointer dereference.
The concurrent scenario that triggers the panic is as follows:
F2FS_WB_CP_DATA write callback umount
- f2fs_write_checkpoint
- f2fs_wait_on_all_pages(sbi, F2FS_WB_CP_DATA)
- blk_mq_end_request
- bio_endio
- f2fs_write_end_io
: dec_page_count(sbi, F2FS_WB_CP_DATA)
: wake_up(&sbi->cp_wait)
- kill_f2fs_super
- kill_block_super
- f2fs_put_super
: iput(sbi->node_inode)
: sbi->node_inode = NULL
: f2fs_in_warm_node_list
- is_node_folio // sbi->node_inode is NULL and panic
The root cause is that f2fs_put_super() calls iput(sbi->node_inode) and
sets sbi->node_inode to NULL after sbi->nr_pages[F2FS_WB_CP_DATA] is
decremented to zero. As a result, f2fs_in_warm_node_list() may
dereference a NULL node_inode when checking whether a folio belongs to
the node inode, leading to a panic.
This patch fixes the issue by calling f2fs_in_warm_node_list() before
decrementing sbi->nr_pages[F2FS_WB_CP_DATA], thus preventing the
use-after-free condition.
CVSS Score
7.8
EPSS Score
0.001
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
fs/ntfs3: validate rec->used in journal-replay file record check
check_file_record() validates rec->total against the record size but
never validates rec->used. The do_action() journal-replay handlers read
rec->used from disk and use it to compute memmove lengths:
DeleteAttribute: memmove(attr, ..., used - asize - roff)
CreateAttribute: memmove(..., attr, used - roff)
change_attr_size: memmove(..., used - PtrOffset(rec, next))
When rec->used is smaller than the offset of a validated attribute, or
larger than the record size, these subtractions can underflow allowing
us to copy huge amounts of memory in to a 4kb buffer, generally
considered a bad idea overall.
This requires a corrupted filesystem, which isn't a threat model the
kernel really needs to worry about, but checking for such an obvious
out-of-bounds value is good to keep things robust, especially on journal
replay
Fix this up by bounding rec->used correctly.
This is much like commit b2bc7c44ed17 ("fs/ntfs3: Fix slab-out-of-bounds
read in DeleteIndexEntryRoot") which checked different values in this
same switch statement.
CVSS Score
7.8
EPSS Score
0.001
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
f2fs: fix use-after-free of sbi in f2fs_compress_write_end_io()
In f2fs_compress_write_end_io(), dec_page_count(sbi, type) can bring
the F2FS_WB_CP_DATA counter to zero, unblocking
f2fs_wait_on_all_pages() in f2fs_put_super() on a concurrent unmount
CPU. The unmount path then proceeds to call
f2fs_destroy_page_array_cache(sbi), which destroys
sbi->page_array_slab via kmem_cache_destroy(), and eventually
kfree(sbi). Meanwhile, the bio completion callback is still executing:
when it reaches page_array_free(sbi, ...), it dereferences
sbi->page_array_slab — a destroyed slab cache — to call
kmem_cache_free(), causing a use-after-free.
This is the same class of bug as CVE-2026-23234 (which fixed the
equivalent race in f2fs_write_end_io() in data.c), but in the
compressed writeback completion path that was not covered by that fix.
Fix this by moving dec_page_count() to after page_array_free(), so
that all sbi accesses complete before the counter decrement that can
unblock unmount. For non-last folios (where atomic_dec_return on
cic->pending_pages is nonzero), dec_page_count is called immediately
before returning — page_array_free is not reached on this path, so
there is no post-decrement sbi access. For the last folio,
page_array_free runs while the F2FS_WB_CP_DATA counter is still
nonzero (this folio has not yet decremented it), keeping sbi alive,
and dec_page_count runs as the final operation.
CVSS Score
7.8
EPSS Score
0.001
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: use check_add_overflow() to prevent u16 DACL size overflow
set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes
in u16 variables. When a file has many POSIX ACL entries, the
accumulated size can wrap past 65535, causing the pointer arithmetic
(char *)pndace + *size to land within already-written ACEs. Subsequent
writes then overwrite earlier entries, and pndacl->size gets a
truncated value.
Use check_add_overflow() at each accumulation point to detect the
wrap before it corrupts the buffer, consistent with existing
check_mul_overflow() usage elsewhere in smbacl.c.
CVSS Score
5.5
EPSS Score
0.001
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate num_aces and harden ACE walk in smb_inherit_dacl()
smb_inherit_dacl() trusts the on-disk num_aces value from the parent
directory's DACL xattr and uses it to size a heap allocation:
aces_base = kmalloc(sizeof(struct smb_ace) * num_aces * 2, ...);
num_aces is a u16 read from le16_to_cpu(parent_pdacl->num_aces)
without checking that it is consistent with the declared pdacl_size.
An authenticated client whose parent directory's security.NTACL is
tampered (e.g. via offline xattr corruption or a concurrent path that
bypasses parse_dacl()) can present num_aces = 65535 with minimal
actual ACE data. This causes a ~8 MB allocation (not kzalloc, so
uninitialized) that the subsequent loop only partially populates, and
may also overflow the three-way size_t multiply on 32-bit kernels.
Additionally, the ACE walk loop uses the weaker
offsetof(struct smb_ace, access_req) minimum size check rather than
the minimum valid on-wire ACE size, and does not reject ACEs whose
declared size is below the minimum.
Reproduced on UML + KASAN + LOCKDEP against the real ksmbd code path.
A legitimate mount.cifs client creates a parent directory over SMB
(ksmbd writes a valid security.NTACL xattr), then the NTACL blob on
the backing filesystem is rewritten to set num_aces = 0xFFFF while
keeping the posix_acl_hash bytes intact so ksmbd_vfs_get_sd_xattr()'s
hash check still passes. A subsequent SMB2 CREATE of a child under
that parent drives smb2_open() into smb_inherit_dacl() (share has
"vfs objects = acl_xattr" set), which fails the page allocator:
WARNING: mm/page_alloc.c:5226 at __alloc_frozen_pages_noprof+0x46c/0x9c0
Workqueue: ksmbd-io handle_ksmbd_work
__alloc_frozen_pages_noprof+0x46c/0x9c0
___kmalloc_large_node+0x68/0x130
__kmalloc_large_node_noprof+0x24/0x70
__kmalloc_noprof+0x4c9/0x690
smb_inherit_dacl+0x394/0x2430
smb2_open+0x595d/0xabe0
handle_ksmbd_work+0x3d3/0x1140
With the patch applied the added guard rejects the tampered value
with -EINVAL before any large allocation runs, smb2_open() falls back
to smb2_create_sd_buffer(), and the child is created with a default
SD. No warning, no splat.
Fix by:
1. Validating num_aces against pdacl_size using the same formula
applied in parse_dacl().
2. Replacing the raw kmalloc(sizeof * num_aces * 2) with
kmalloc_array(num_aces * 2, sizeof(...)) for overflow-safe
allocation.
3. Tightening the per-ACE loop guard to require the minimum valid
ACE size (offsetof(smb_ace, sid) + CIFS_SID_BASE_SIZE) and
rejecting under-sized ACEs, matching the hardening in
smb_check_perm_dacl() and parse_dacl().
v1 -> v2:
- Replace the synthetic test-module splat in the changelog with a
real-path UML + KASAN reproduction driven through mount.cifs and
SMB2 CREATE; Namjae flagged the kcifs3_test_inherit_dacl_old name
in v1 since it does not exist in ksmbd.
- Drop the commit-hash citation from the code comment per Namjae's
review; keep the parse_dacl() pointer.
CVSS Score
8.8
EPSS Score
0.004
Published
2026-05-01
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.
CVSS Score
7.1
EPSS Score
0.001
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix OOB read in smb2_ioctl_query_info QUERY_INFO path
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.
CVSS Score
8.1
EPSS Score
0.003
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
smb: client: validate the whole DACL before rewriting it in cifsacl
build_sec_desc() and id_mode_to_cifs_acl() derive a DACL pointer from a
server-supplied dacloffset and then use the incoming ACL to rebuild the
chmod/chown security descriptor.
The original fix only checked that the struct smb_acl header fits before
reading dacl_ptr->size or dacl_ptr->num_aces. That avoids the immediate
header-field OOB read, but the rewrite helpers still walk ACEs based on
pdacl->num_aces with no structural validation of the incoming DACL body.
A malicious server can return a truncated DACL that still contains a
header, claims one or more ACEs, and then drive
replace_sids_and_copy_aces() or set_chmod_dacl() past the validated
extent while they compare or copy attacker-controlled ACEs.
Factor the DACL structural checks into validate_dacl(), extend them to
validate each ACE against the DACL bounds, and use the shared validator
before the chmod/chown rebuild paths. parse_dacl() reuses the same
validator so the read-side parser and write-side rewrite paths agree on
what constitutes a well-formed incoming DACL.
CVSS Score
8.8
EPSS Score
0.003
Published
2026-05-01
In the Linux kernel, the following vulnerability has been resolved:
fuse: reject oversized dirents in page cache
fuse_add_dirent_to_cache() computes a serialized dirent size from the
server-controlled namelen field and copies the dirent into a single
page-cache page. The existing logic only checks whether the dirent fits
in the remaining space of the current page and advances to a fresh page
if not. It never checks whether the dirent itself exceeds PAGE_SIZE.
As a result, a malicious FUSE server can return a dirent with
namelen=4095, producing a serialized record size of 4120 bytes. On 4 KiB
page systems this causes memcpy() to overflow the cache page by 24 bytes
into the following kernel page.
Reject dirents that cannot fit in a single page before copying them into
the readdir cache.
CVSS Score
7.8
EPSS Score
0.001
Published
2026-05-01