Re: [PATCH] apparmor: avoid crash when parsed profile name is empty

[John Johansen]

On 12/28/23 08:07, Fedor Pchelkin wrote:
> 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).
>
> Fixes: 04dc715e24d0 ("apparmor: audit policy ns specified in policy load")
> Signed-off-by: Fedor Pchelkin <pchelkin@xxxxxxxxx>

thanks, I have pulled this into my tree

Acked-by: John Johansen <john.johansen@xxxxxxxxxxxxx>

> ---
>   security/apparmor/policy_unpack.c | 4 ++++
>   1 file changed, 4 insertions(+)
>
> diff --git a/security/apparmor/policy_unpack.c b/security/apparmor/policy_unpack.c
> index e0af1e9f40ee..70d448048773 100644
> --- a/security/apparmor/policy_unpack.c
> +++ b/security/apparmor/policy_unpack.c
> @@ -835,6 +835,10 @@ static struct aa_profile *unpack_profile(struct aa_ext *e, char **ns_name)
>   
>   	tmpname = aa_splitn_fqname(name, strlen(name), &tmpns, &ns_len);
>   	if (tmpns) {
> +		if (!tmpname) {
> +			info = "empty profile name";
> +			goto fail;
> +		}
>   		*ns_name = kstrndup(tmpns, ns_len, GFP_KERNEL);
>   		if (!*ns_name) {
>   			info = "out of memory";