On Tue, 2022-11-22 at 14:39 -0500, Mimi Zohar wrote:
> Hi Roberto,
>
> On Fri, 2022-11-04 at 13:20 +0100, Roberto Sassu wrote:
> > From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> >
> > Commit ac4e97abce9b8 ("scatterlist: sg_set_buf() argument must be in linear
> > mapping") requires that both the signature and the digest resides in the
> > linear mapping area.
> >
> > However, more recently commit ba14a194a434c ("fork: Add generic vmalloced
> > stack support"), made it possible to move the stack in the vmalloc area,
> > which could make the requirement of the first commit not satisfied anymore.
> >
> > If CONFIG_SG=y and CONFIG_VMAP_STACK=y, the following BUG() is triggered:
>
> ^CONFIG_DEBUG_SG
>
> > [ 467.077359] kernel BUG at include/linux/scatterlist.h:163!
> > [ 467.077939] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
> >
> > [...]
> >
> > [ 467.095225] Call Trace:
> > [ 467.096088] <TASK>
> > [ 467.096928] ? rcu_read_lock_held_common+0xe/0x50
> > [ 467.097569] ? rcu_read_lock_sched_held+0x13/0x70
> > [ 467.098123] ? trace_hardirqs_on+0x2c/0xd0
> > [ 467.098647] ? public_key_verify_signature+0x470/0x470
> > [ 467.099237] asymmetric_verify+0x14c/0x300
> > [ 467.099869] evm_verify_hmac+0x245/0x360
> > [ 467.100391] evm_inode_setattr+0x43/0x190
> >
> > The failure happens only for the digest, as the pointer comes from the
> > stack, and not for the signature, which instead was allocated by
> > vfs_getxattr_alloc().
>
> Only after enabling CONFIG_DEBUG_SG does EVM fail.
>
> > Fix this by making a copy of both in asymmetric_verify(), so that the
> > linear mapping requirement is always satisfied, regardless of the caller.
>
> As only EVM is affected, it would make more sense to limit the change
> to EVM.
I found another occurrence:
static int xattr_verify(enum ima_hooks func, struct integrity_iint_cache *iint,
struct evm_ima_xattr_data *xattr_value, int xattr_len,
enum integrity_status *status, const char **cause)
{
[...]
rc = integrity_digsig_verify(INTEGRITY_KEYRING_IMA,
(const char *)xattr_value,
xattr_len, hash.digest,
hash.hdr.length);
Should I do two patches?
Thanks
Roberto
