Re: [PATCH v4 2/3] audit: add support for the openat2 syscall

On 2022-02-09 16:18, Paul Moore wrote: > On Wed, Feb 9, 2022 at 10:57 AM Paul Moore <paul(a)paul-moore.com&gt; wrote: > > On Tue, Feb 8, 2022 at 10:44 PM Jeff Mahoney <jeffm(a)suse.com&gt; wrote: > > > > > > Hi Richard - > > > > > > On 5/19/21 16:00, Richard Guy Briggs wrote: > > > > The openat2(2) syscall was added in kernel v5.6 with commit fddb5d430ad9 > > > > ("open: introduce openat2(2) syscall") > > > > > > > > Add the openat2(2) syscall to the audit syscall classifier. > > > > > > > > Link: https://github.com/linux-audit/audit-kernel/issues/67 > > > > Signed-off-by: Richard Guy Briggs <rgb(a)redhat.com&gt; > > > > Link: https://lore.kernel.org/r/f5f1a4d8699613f8c02ce762807228c841c2e26f.162136... > > > > --- > > > > > > [...] > > > > > > > diff --git a/kernel/auditsc.c b/kernel/auditsc.c > > > > index d775ea16505b..3f59ab209dfd 100644 > > > > --- a/kernel/auditsc.c > > > > +++ b/kernel/auditsc.c > > > > @@ -76,6 +76,7 @@ > > > > #include <linux/fsnotify_backend.h> > > > > #include <uapi/linux/limits.h> > > > > #include <uapi/linux/netfilter/nf_tables.h> > > > > +#include <uapi/linux/openat2.h> > > > > > > > > #include "audit.h" > > > > > > > > @@ -196,6 +197,8 @@ static int audit_match_perm(struct audit_context *ctx, int mask) > > > > return ((mask & AUDIT_PERM_WRITE) && ctx->argv[0] == SYS_BIND); > > > > case AUDITSC_EXECVE: > > > > return mask & AUDIT_PERM_EXEC; > > > > + case AUDITSC_OPENAT2: > > > > + return mask & ACC_MODE((u32)((struct open_how *)ctx->argv[2])->flags); > > > > default: > > > > return 0; > > > > } > > > > > > ctx->argv[2] holds a userspace pointer and can't be dereferenced like this. > > > > > > I'm getting oopses, like so: > > > BUG: unable to handle page fault for address: 00007fff961bbe70 > > > > Thanks Jeff. > > > > Yes, this is obviously the wrong thing to being doing; I remember > > checking to make sure we placed the audit_openat2_how() hook after the > > open_how was copied from userspace, but I missed the argv dereference > > in the syscall exit path when reviewing the code. > > > > Richard, as we are already copying the open_how info into > > audit_context::openat2 safely, the obvious fix is to convert > > audit_match_perm() to use the previously copied value instead of argv. > > If you can't submit a patch for this today please let me know. > > I haven't heard anything from Richard so I put together a patch which > should fix the problem (link below). It's currently untested, but > I've got a kernel building now with the patch ... Well, the day wasn't over yet... I've compiled and tested it.