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Date: Tue, 08 Oct 2013 17:49:18 -0700
From: Joe Perches <joe@...ches.com>
To: Ryan Mallon <rmallon@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, eldad@...refinery.com, Jiri
Kosina <jkosina@...e.cz>, jgunthorpe@...idianresearch.com, Dan Rosenberg
<dan.j.rosenberg@...il.com>, Kees Cook <keescook@...omium.org>, Alexander
Viro <viro@...iv.linux.org.uk>, "Eric W. Biederman"
<ebiederm@...ssion.com>, George Spelvin <linux@...izon.com>,
"kernel-hardening@...ts.openwall.com"
<kernel-hardening@...ts.openwall.com>, "linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] vsprintf: Check real user/group id for %pK
On Wed, 2013-10-09 at 11:15 +1100, Ryan Mallon wrote:
> Some setuid binaries will allow reading of files which have read
> permission by the real user id. This is problematic with files which
> use %pK because the file access permission is checked at open() time,
> but the kptr_restrict setting is checked at read() time. If a setuid
> binary opens a %pK file as an unprivileged user, and then elevates
> permissions before reading the file, then kernel pointer values may be
> leaked.
I think it should explicitly test 0.
Dan? Might this be any problem?
Otherwise, just style notes:
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
[]
> @@ -1312,10 +1312,26 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
> spec.field_width = default_width;
> return string(buf, end, "pK-error", spec);
> }
> - if (!((kptr_restrict == 0) ||
> - (kptr_restrict == 1 &&
> - has_capability_noaudit(current, CAP_SYSLOG))))
> - ptr = NULL;
> +
> + /*
> + * If kptr_restrict is set to 2, then %pK always prints as
> + * NULL. If it is set to 1, then only print the real pointer
> + * value if the current proccess has CAP_SYSLOG and is running
> + * with the same credentials it started with. This is because
> + * access to files is checked at open() time, but %pK checks
> + * permission at read() time. We don't want to leak pointer
> + * values if a binary opens a file using %pK and then elevates
> + * privileges before reading it.
> + */
> + {
> + const struct cred *cred = current_cred();
Please add #include <linux/cred.h>
> + if (kptr_restrict == 2 || (kptr_restrict == 1 &&
> + (!has_capability_noaudit(current, CAP_SYSLOG) ||
> + !uid_eq(cred->euid, cred->uid) ||
> + !gid_eq(cred->egid, cred->gid))))
> + ptr = NULL;
> + }
> break;
Also, it might be easier to read as:
if (kptr_restrict == 0)
break;
else if (kptr_restrict == 1) {
const struct cred *cred = current_cred();
if (!has_capability_noaudit(current, CAP_SYSLOG) ||
!uid_eq(cred->euid, cred->uid) ||
!gid_eq(cred->egid, cred->gid))
ptr = NULL;
} else {
ptr = NULL;
}
break;
> case 'N':
> switch (fmt[1]) {
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