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Wed, 09 Feb 2022 14:29:32 -0800 (PST) MIME-Version: 1.0 References: <20220209214048.GF1708086@madcap2.tricolour.ca> In-Reply-To: <20220209214048.GF1708086@madcap2.tricolour.ca> From: Paul Moore Date: Wed, 9 Feb 2022 17:29:21 -0500 Message-ID: Subject: Re: [PATCH v4 2/3] audit: add support for the openat2 syscall To: Richard Guy Briggs Cc: Jeff Mahoney , Linux-Audit Mailing List , LKML , linux-fsdevel@vger.kernel.org, Eric Paris , Steve Grubb , Alexander Viro , Eric Paris , Tony Jones Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 9, 2022 at 4:41 PM Richard Guy Briggs wrote: > On 2022-02-09 10:57, Paul Moore wrote: > > On Tue, Feb 8, 2022 at 10:44 PM Jeff Mahoney 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 > > > > Link: https://lore.kernel.org/r/f5f1a4d8699613f8c02ce762807228c841c2e26f.1621363275.git.rgb@redhat.com > > > > --- > > > > > > [...] > > > > > > > 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 > > > > #include > > > > #include > > > > +#include > > > > > > > > #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. > > Agreed. It would have been more awkward with the original order of the > patches. > > The syscalls_file test in the audit-testsuite should have caught this. > https://github.com/rgbriggs/audit-testsuite/commit/1c99021ae27ea23eccce2bb1861df4c9c665cd5b > The test provided does essentially the same thing. I would have thought so, but I've now run this multiple times on both affected and patched kernels but I don't see the page fault on my test system. Anyway, that test has now been merged with the audit-testsuite as well as some cleanup on top to test for the new OPENAT2 record when applicable. -- paul-moore.com