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 aasplitnfqname().

aasplitnfqname() treats ":samba-dcerpcd" as only containing a namespace. Thus it returns NULL for tmpname, meanwhile tmpns is non-NULL. Later aaallocprofile() 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: apparmorparser 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 aapolicyinit+0x1bb/0x230 aaallocprofile+0xb1/0x480 unpackprofile+0x3bc/0x4960 aaunpack+0x309/0x15e0 aareplaceprofiles+0x213/0x33c0 policyupdate+0x261/0x370 profilereplace+0x20e/0x2a0 vfswrite+0x2af/0xe00 ksyswrite+0x126/0x250 dosyscall64+0x46/0xf0 entrySYSCALL64after_hwframe+0x6e/0x76 </TASK> ---[ end trace 0000000000000000 ]--- RIP: 0010:strlen+0x1e/0xa0

It seems such behaviour of aasplitnfqname() is expected and checked in other places where it is called (e.g. aaremoveprofiles). 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).