CVE-2023-52443

In the Linux kernel, the following vulnerability has been resolved:
apparmor: avoid crash when parsed profile name is empty When processing a
packed profile in unpack_profile() described like “profile
:ns::samba-dcerpcd /usr/lib*/samba/{,samba/}samba-dcerpcd {…}” a string
“:samba-dcerpcd” is unpacked as a fully-qualified name and then passed to
aa_splitn_fqname(). aa_splitn_fqname() treats “:samba-dcerpcd” as only
containing a namespace. Thus it returns NULL for tmpname, meanwhile tmpns
is non-NULL. Later aa_alloc_profile() crashes as the new profile name is
NULL now. general protection fault, probably for non-canonical address
0xdffffc0000000000: 0000 [#1] PREEMPT SMP KASAN NOPTI KASAN: null-ptr-deref
in range [0x0000000000000000-0x0000000000000007] CPU: 6 PID: 1657 Comm:
apparmor_parser Not tainted 6.7.0-rc2-dirty #16 Hardware name: QEMU
Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.16.2-3-gd478f380-rebuilt.opensuse.org 04/01/2014 RIP:
0010:strlen+0x1e/0xa0 Call Trace: <TASK> ? strlen+0x1e/0xa0
aa_policy_init+0x1bb/0x230 aa_alloc_profile+0xb1/0x480
unpack_profile+0x3bc/0x4960 aa_unpack+0x309/0x15e0
aa_replace_profiles+0x213/0x33c0 policy_update+0x261/0x370
profile_replace+0x20e/0x2a0 vfs_write+0x2af/0xe00 ksys_write+0x126/0x250
do_syscall_64+0x46/0xf0 entry_SYSCALL_64_after_hwframe+0x6e/0x76 </TASK>
—[ end trace 0000000000000000 ]— RIP: 0010:strlen+0x1e/0xa0 It seems
such behaviour of aa_splitn_fqname() is expected and checked in other
places where it is called (e.g. aa_remove_profiles). Well, there is an
explicit comment “a ns name without a following profile is allowed” inside.
AFAICS, nothing can prevent unpacked “name” to be in form like
“:samba-dcerpcd” - it is passed from userspace. Deny the whole profile set
replacement in such case and inform user with EPROTO and an explaining
message. Found by Linux Verification Center (linuxtesting.org).

Notes