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security: add trace event for cap_capable

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In cases where we want a stable way to observe/trace
cap_capable (e.g. protection from inlining and API updates)
add a tracepoint that passes:
- The credentials used
- The user namespace of the resource being accessed
- The user namespace in which the credential provides the
capability to access the targeted resource
- The capability to check for
- The return value of the check

Signed-off-by: Jordan Rome <linux@jordanrome.com>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Paul Moore <paul@paul-moore.com>
Reviewed-by: Serge Hallyn <serge@hallyn.com>
Link: https://lore.kernel.org/r/20241204155911.1817092-1-linux@jordanrome.com
Signed-off-by: Serge Hallyn <sergeh@kernel.org>
This commit is contained in:
Jordan Rome 2024-12-04 07:59:11 -08:00 committed by Serge Hallyn
parent 3f4f1f8a1a
commit d48da4d5ed
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GPG Key ID: 3570DA17270ACE24
3 changed files with 99 additions and 13 deletions
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1
MAINTAINERS
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@ -5147,6 +5147,7 @@ M: Serge Hallyn <serge@hallyn.com>
L: linux-security-module@vger.kernel.org
S: Supported
F: include/linux/capability.h
F: include/trace/events/capability.h
F: include/uapi/linux/capability.h
F: kernel/capability.c
F: security/commoncap.c

57
include/trace/events/capability.h Normal file
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@ -0,0 +1,57 @@
/* SPDX-License-Identifier: GPL-2.0 */
#undef TRACE_SYSTEM
#define TRACE_SYSTEM capability
#if !defined(_TRACE_CAPABILITY_H) || defined(TRACE_HEADER_MULTI_READ)
#define _TRACE_CAPABILITY_H
#include <linux/cred.h>
#include <linux/tracepoint.h>
#include <linux/user_namespace.h>
/**
* cap_capable - called after it's determined if a task has a particular
* effective capability
*
* @cred: The credentials used
* @target_ns: The user namespace of the resource being accessed
* @capable_ns: The user namespace in which the credential provides the
* capability to access the targeted resource.
* This will be NULL if ret is not 0.
* @cap: The capability to check for
* @ret: The return value of the check: 0 if it does, -ve if it does not
*
* Allows to trace calls to cap_capable in commoncap.c
*/
TRACE_EVENT(cap_capable,
TP_PROTO(const struct cred *cred, struct user_namespace *target_ns,
const struct user_namespace *capable_ns, int cap, int ret),
TP_ARGS(cred, target_ns, capable_ns, cap, ret),
TP_STRUCT__entry(
__field(const struct cred *, cred)
__field(struct user_namespace *, target_ns)
__field(const struct user_namespace *, capable_ns)
__field(int, cap)
__field(int, ret)
),
TP_fast_assign(
__entry->cred = cred;
__entry->target_ns = target_ns;
__entry->capable_ns = ret == 0 ? capable_ns : NULL;
__entry->cap = cap;
__entry->ret = ret;
),
TP_printk("cred %p, target_ns %p, capable_ns %p, cap %d, ret %d",
__entry->cred, __entry->target_ns, __entry->capable_ns, __entry->cap,
__entry->ret)
);
#endif /* _TRACE_CAPABILITY_H */
/* This part must be outside protection */
#include <trace/define_trace.h>

54
security/commoncap.c
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@ -27,6 +27,9 @@
#include <linux/mnt_idmapping.h>
#include <uapi/linux/lsm.h>
#define CREATE_TRACE_POINTS
#include <trace/events/capability.h>
/*
* If a non-root user executes a setuid-root binary in
* !secure(SECURE_NOROOT) mode, then we raise capabilities.
@ -50,24 +53,24 @@ static void warn_setuid_and_fcaps_mixed(const char *fname)
}
/**
* cap_capable - Determine whether a task has a particular effective capability
* cap_capable_helper - Determine whether a task has a particular effective
* capability.
* @cred: The credentials to use
* @targ_ns: The user namespace in which we need the capability
* @target_ns: The user namespace of the resource being accessed
* @cred_ns: The user namespace of the credentials
* @cap: The capability to check for
* @opts: Bitmask of options defined in include/linux/security.h
*
* Determine whether the nominated task has the specified capability amongst
* its effective set, returning 0 if it does, -ve if it does not.
*
* NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
* and has_capability() functions. That is, it has the reverse semantics:
* cap_has_capability() returns 0 when a task has a capability, but the
* kernel's capable() and has_capability() returns 1 for this case.
* See cap_capable for more details.
*/
int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
int cap, unsigned int opts)
static inline int cap_capable_helper(const struct cred *cred,
struct user_namespace *target_ns,
const struct user_namespace *cred_ns,
int cap)
{
struct user_namespace *ns = targ_ns;
struct user_namespace *ns = target_ns;
/* See if cred has the capability in the target user namespace
* by examining the target user namespace and all of the target
@ -75,21 +78,21 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
*/
for (;;) {
/* Do we have the necessary capabilities? */
if (ns == cred->user_ns)
if (likely(ns == cred_ns))
return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
/*
* If we're already at a lower level than we're looking for,
* we're done searching.
*/
if (ns->level <= cred->user_ns->level)
if (ns->level <= cred_ns->level)
return -EPERM;
/*
* The owner of the user namespace in the parent of the
* user namespace has all caps.
*/
if ((ns->parent == cred->user_ns) && uid_eq(ns->owner, cred->euid))
if ((ns->parent == cred_ns) && uid_eq(ns->owner, cred->euid))
return 0;
/*
@ -102,6 +105,31 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
/* We never get here */
}
/**
* cap_capable - Determine whether a task has a particular effective capability
* @cred: The credentials to use
* @target_ns: The user namespace of the resource being accessed
* @cap: The capability to check for
* @opts: Bitmask of options defined in include/linux/security.h (unused)
*
* Determine whether the nominated task has the specified capability amongst
* its effective set, returning 0 if it does, -ve if it does not.
*
* NOTE WELL: cap_has_capability() cannot be used like the kernel's capable()
* and has_capability() functions. That is, it has the reverse semantics:
* cap_has_capability() returns 0 when a task has a capability, but the
* kernel's capable() and has_capability() returns 1 for this case.
*/
int cap_capable(const struct cred *cred, struct user_namespace *target_ns,
int cap, unsigned int opts)
{
const struct user_namespace *cred_ns = cred->user_ns;
int ret = cap_capable_helper(cred, target_ns, cred_ns, cap);
trace_cap_capable(cred, target_ns, cred_ns, cap, ret);
return ret;
}
/**
* cap_settime - Determine whether the current process may set the system clock
* @ts: The time to set