On 5/24/26 22:37, Zhang Cen wrote:
> f2fs_acl_count() only validates the aggregate ACL xattr length. A
> malformed ACL can still place ACL_USER or ACL_GROUP in a slot that only
> contains struct f2fs_acl_entry_short bytes, and f2fs_acl_from_disk()
> then reads entry->e_id before verifying that a full entry fits.
>
> Require a short entry before reading e_tag and e_perm, and require a
> full entry before reading e_id for ACL_USER and ACL_GROUP. This keeps
> corrupted ACL xattrs on the existing -EINVAL path without reading past
> the copied xattr value.
>
> Validation reproduced this kernel report:
> KASAN slab-out-of-bounds in __f2fs_get_acl+0x6fb/0x7e0
> RIP: 0033:0x7f4b835ea7aa
> The buggy address belongs to the object at ffff888114589960 which belongs
> to the cache kmalloc-8 of size 8
> The buggy address is located 0 bytes to the right of allocated 8-byte
> region [ffff888114589960, ffff888114589968)
> Read of size 4
> Call trace:
> dump_stack_lvl+0x66/0xa0 (?:?)
> print_report+0xce/0x630 (?:?)
> __f2fs_get_acl+0x6fb/0x7e0 (fs/f2fs/acl.c:169)
> srso_alias_return_thunk+0x5/0xfbef5 (?:?)
> __virt_addr_valid+0x224/0x430 (?:?)
> kasan_report+0xe0/0x110 (?:?)
> __f2fs_get_acl+0x5/0x7e0 (fs/f2fs/acl.c:169)
> __get_acl+0x281/0x380 (?:?)
> vfs_get_acl+0x10b/0x190 (?:?)
> do_get_acl+0x2a/0x410 (?:?)
> do_get_acl+0x9/0x410 (?:?)
> do_getxattr+0xe8/0x260 (?:?)
> filename_getxattr+0xd1/0x140 (?:?)
> do_getname+0x2d/0x2d0 (?:?)
> path_getxattrat+0x16c/0x200 (?:?)
> lock_release+0xc8/0x290 (?:?)
> cgroup_update_frozen+0x9d/0x320 (?:?)
> lockdep_hardirqs_on_prepare+0xea/0x1a0 (?:?)
> trace_hardirqs_on+0x1a/0x170 (?:?)
> _raw_spin_unlock_irq+0x28/0x50 (?:?)
> do_syscall_64+0x115/0x6a0 (arch/x86/entry/syscall_64.c:87)
> entry_SYSCALL_64_after_hwframe+0x77/0x7f (?:?)
>
> Fixes: af48b85b8cd3 ("f2fs: add xattr and acl functionalities")
> Assisted-by: Codex:gpt-5.5
> Signed-off-by: Zhang Cen <[email protected]>
> ---
> fs/f2fs/acl.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/fs/f2fs/acl.c b/fs/f2fs/acl.c
> index fa8d81a30fb9..290fee451637 100644
> --- a/fs/f2fs/acl.c
> +++ b/fs/f2fs/acl.c
> @@ -70,7 +70,7 @@ static struct posix_acl *f2fs_acl_from_disk(const char
> *value, size_t size)
>
> for (i = 0; i < count; i++) {
>
> - if ((char *)entry > end)
> + if ((char *)entry + sizeof(struct f2fs_acl_entry_short) > end)
unlikely()?
Should return -EFSCORRUPTED instead of -EINVAL?
> goto fail;
>
> acl->a_entries[i].e_tag = le16_to_cpu(entry->e_tag);
> @@ -86,6 +86,8 @@ static struct posix_acl *f2fs_acl_from_disk(const char
> *value, size_t size)
> break;
>
> case ACL_USER:
> + if ((char *)entry + sizeof(struct f2fs_acl_entry) > end)
Ditto,
> + goto fail;
> acl->a_entries[i].e_uid =
> make_kuid(&init_user_ns,
> le32_to_cpu(entry->e_id));
> @@ -93,6 +95,8 @@ static struct posix_acl *f2fs_acl_from_disk(const char
> *value, size_t size)
> sizeof(struct f2fs_acl_entry));
> break;
> case ACL_GROUP:
> + if ((char *)entry + sizeof(struct f2fs_acl_entry) > end)
Ditto,
Thanks,
> + goto fail;
> acl->a_entries[i].e_gid =
> make_kgid(&init_user_ns,
> le32_to_cpu(entry->e_id));
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