Ocfs2 devel - Mar 2023 - ocfs2 xattr

On Mon, 2023-03-06 at 11:45 +0100, Valentin Vidi? wrote:
> On Mon, Mar 06, 2023 at 10:13:45AM +0100, Roberto Sassu wrote:
> > which LSMs are you running?
> 
> This is on Debian, so AppArmor is on by default. It seems like
> only SELinux and SMACK have hooks for inode_init_security so
> for other LSMs 'const char **name' would not get set?
If there is no hook registering to inode_init_security, theoretically
the LSM infrastructure should return -EOPNOTSUPP, which causes ocfs2 to
set si->enable to zero, and not execute the line that causes the kernel
to panic.

The problem would arise if somehow the LSM infrastructure returns zero,
without setting the xattr. That would explain the panic.

Not sure, I will think more.

Roberto

On Mon, Mar 06, 2023 at 05:58:30PM +0100, Roberto Sassu
wrote:
> If there is no hook registering to inode_init_security, theoretically
> the LSM infrastructure should return -EOPNOTSUPP, which causes ocfs2 to
> set si->enable to zero, and not execute the line that causes the kernel
> to panic.
> 
> The problem would arise if somehow the LSM infrastructure returns zero,
> without setting the xattr. That would explain the panic.
> 
> Not sure, I will think more.
Seems you are right. First of all, there is more than one LSM active:

[    0.048241] LSM: initializing
lsm=lockdown,capability,landlock,yama,integrity,apparmor,tomoyo,bpf
[    0.048250] landlock: Up and running.
[    0.048250] Yama: becoming mindful.
[    0.048293] AppArmor: AppArmor initialized
[    0.048295] TOMOYO Linux initialized
[    0.048300] LSM support for eBPF active

But from the source it seems that eBPF creates all hooks and returns the
default value of 0 for inode_init_security:

include/linux/lsm_hook_defs.h:LSM_HOOK(int, 0, inode_init_security, struct inode
*inode,

kernel/bpf/bpf_lsm.c:#define LSM_HOOK(RET, DEFAULT, NAME, ...)  \
kernel/bpf/bpf_lsm.c:noinline RET bpf_lsm_##NAME(__VA_ARGS__)   \
kernel/bpf/bpf_lsm.c:{                                          \
kernel/bpf/bpf_lsm.c:   return DEFAULT;                         \
kernel/bpf/bpf_lsm.c:}

I suppose the fix would be to change the default value to -EOPNOTSUPP?

-- 
Valentin