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: ? 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).

Weakness

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.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/0a12db736edbb4933e4274932aeea594b5876fa4
• https://git.kernel.org/stable/c/1d8e62b5569cc1466ceb8a7e4872cf10160a9dcf
• https://git.kernel.org/stable/c/55a8210c9e7d21ff2644809699765796d4bfb200
• https://git.kernel.org/stable/c/5c0392fdafb0a2321311900be83ffa572bef8203
• https://git.kernel.org/stable/c/5ff00408e5029d3550ee77f62dc15f1e15c47f87
• https://git.kernel.org/stable/c/77ab09b92f16c8439a948d1af489196953dc4a0e
• https://git.kernel.org/stable/c/9286ee97aa4803d99185768735011d0d65827c9e
• https://git.kernel.org/stable/c/9d4fa5fe2b1d56662afd14915a73b4d0783ffa45
• https://git.kernel.org/stable/c/0a12db736edbb4933e4274932aeea594b5876fa4
• https://git.kernel.org/stable/c/1d8e62b5569cc1466ceb8a7e4872cf10160a9dcf
• https://git.kernel.org/stable/c/55a8210c9e7d21ff2644809699765796d4bfb200
• https://git.kernel.org/stable/c/5c0392fdafb0a2321311900be83ffa572bef8203
• https://git.kernel.org/stable/c/5ff00408e5029d3550ee77f62dc15f1e15c47f87
• https://git.kernel.org/stable/c/77ab09b92f16c8439a948d1af489196953dc4a0e
• https://git.kernel.org/stable/c/9286ee97aa4803d99185768735011d0d65827c9e
• https://git.kernel.org/stable/c/9d4fa5fe2b1d56662afd14915a73b4d0783ffa45
• https://lists.debian.org/debian-lts-announce/2024/06/msg00016.html
• https://lists.debian.org/debian-lts-announce/2024/06/msg00020.html