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: ? 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 —[ 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).
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Linux_kernel | Linux | * | 4.19.306 (excluding) |
| Linux_kernel | Linux | 4.20 (including) | 5.4.268 (excluding) |
| Linux_kernel | Linux | 5.5.0 (including) | 5.10.209 (excluding) |
| Linux_kernel | Linux | 5.11.0 (including) | 5.15.148 (excluding) |
| Linux_kernel | Linux | 5.16.0 (including) | 6.1.75 (excluding) |
| Linux_kernel | Linux | 6.2.0 (including) | 6.6.14 (excluding) |
| Linux_kernel | Linux | 6.7.0 (including) | 6.7.2 (excluding) |