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authorDavid Howells <dhowells@redhat.com>2009-01-06 22:27:01 +0000
committerJames Morris <jmorris@namei.org>2009-01-07 09:38:48 +1100
commit3699c53c485bf0168e6500d0ed18bf931584dd7c (patch)
treeeee63a8ddbdb0665bc6a4a053a2405ca7a5b867f /security
parent29881c4502ba05f46bc12ae8053d4e08d7e2615c (diff)
downloadlinux-2.6.38-lt-ux500-3699c53c485bf0168e6500d0ed18bf931584dd7c.tar.gz
CRED: Fix regression in cap_capable() as shown up by sys_faccessat() [ver #3]
Fix a regression in cap_capable() due to: commit 3b11a1decef07c19443d24ae926982bc8ec9f4c0 Author: David Howells <dhowells@redhat.com> Date: Fri Nov 14 10:39:26 2008 +1100 CRED: Differentiate objective and effective subjective credentials on a task The problem is that the above patch allows a process to have two sets of credentials, and for the most part uses the subjective credentials when accessing current's creds. There is, however, one exception: cap_capable(), and thus capable(), uses the real/objective credentials of the target task, whether or not it is the current task. Ordinarily this doesn't matter, since usually the two cred pointers in current point to the same set of creds. However, sys_faccessat() makes use of this facility to override the credentials of the calling process to make its test, without affecting the creds as seen from other processes. One of the things sys_faccessat() does is to make an adjustment to the effective capabilities mask, which cap_capable(), as it stands, then ignores. The affected capability check is in generic_permission(): if (!(mask & MAY_EXEC) || execute_ok(inode)) if (capable(CAP_DAC_OVERRIDE)) return 0; This change passes the set of credentials to be tested down into the commoncap and SELinux code. The security functions called by capable() and has_capability() select the appropriate set of credentials from the process being checked. This can be tested by compiling the following program from the XFS testsuite: /* * t_access_root.c - trivial test program to show permission bug. * * Written by Michael Kerrisk - copyright ownership not pursued. * Sourced from: http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-10/6030.html */ #include <limits.h> #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <fcntl.h> #include <sys/stat.h> #define UID 500 #define GID 100 #define PERM 0 #define TESTPATH "/tmp/t_access" static void errExit(char *msg) { perror(msg); exit(EXIT_FAILURE); } /* errExit */ static void accessTest(char *file, int mask, char *mstr) { printf("access(%s, %s) returns %d\n", file, mstr, access(file, mask)); } /* accessTest */ int main(int argc, char *argv[]) { int fd, perm, uid, gid; char *testpath; char cmd[PATH_MAX + 20]; testpath = (argc > 1) ? argv[1] : TESTPATH; perm = (argc > 2) ? strtoul(argv[2], NULL, 8) : PERM; uid = (argc > 3) ? atoi(argv[3]) : UID; gid = (argc > 4) ? atoi(argv[4]) : GID; unlink(testpath); fd = open(testpath, O_RDWR | O_CREAT, 0); if (fd == -1) errExit("open"); if (fchown(fd, uid, gid) == -1) errExit("fchown"); if (fchmod(fd, perm) == -1) errExit("fchmod"); close(fd); snprintf(cmd, sizeof(cmd), "ls -l %s", testpath); system(cmd); if (seteuid(uid) == -1) errExit("seteuid"); accessTest(testpath, 0, "0"); accessTest(testpath, R_OK, "R_OK"); accessTest(testpath, W_OK, "W_OK"); accessTest(testpath, X_OK, "X_OK"); accessTest(testpath, R_OK | W_OK, "R_OK | W_OK"); accessTest(testpath, R_OK | X_OK, "R_OK | X_OK"); accessTest(testpath, W_OK | X_OK, "W_OK | X_OK"); accessTest(testpath, R_OK | W_OK | X_OK, "R_OK | W_OK | X_OK"); exit(EXIT_SUCCESS); } /* main */ This can be run against an Ext3 filesystem as well as against an XFS filesystem. If successful, it will show: [root@andromeda src]# ./t_access_root /tmp/xxx 0 4043 4043 ---------- 1 dhowells dhowells 0 2008-12-31 03:00 /tmp/xxx access(/tmp/xxx, 0) returns 0 access(/tmp/xxx, R_OK) returns 0 access(/tmp/xxx, W_OK) returns 0 access(/tmp/xxx, X_OK) returns -1 access(/tmp/xxx, R_OK | W_OK) returns 0 access(/tmp/xxx, R_OK | X_OK) returns -1 access(/tmp/xxx, W_OK | X_OK) returns -1 access(/tmp/xxx, R_OK | W_OK | X_OK) returns -1 If unsuccessful, it will show: [root@andromeda src]# ./t_access_root /tmp/xxx 0 4043 4043 ---------- 1 dhowells dhowells 0 2008-12-31 02:56 /tmp/xxx access(/tmp/xxx, 0) returns 0 access(/tmp/xxx, R_OK) returns -1 access(/tmp/xxx, W_OK) returns -1 access(/tmp/xxx, X_OK) returns -1 access(/tmp/xxx, R_OK | W_OK) returns -1 access(/tmp/xxx, R_OK | X_OK) returns -1 access(/tmp/xxx, W_OK | X_OK) returns -1 access(/tmp/xxx, R_OK | W_OK | X_OK) returns -1 I've also tested the fix with the SELinux and syscalls LTP testsuites. Signed-off-by: David Howells <dhowells@redhat.com> Tested-by: J. Bruce Fields <bfields@citi.umich.edu> Acked-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: James Morris <jmorris@namei.org>
Diffstat (limited to 'security')
-rw-r--r--security/commoncap.c29
-rw-r--r--security/security.c26
-rw-r--r--security/selinux/hooks.c16
3 files changed, 46 insertions, 25 deletions
diff --git a/security/commoncap.c b/security/commoncap.c
index 79713545cd6..f0e671dcfff 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -45,26 +45,22 @@ EXPORT_SYMBOL(cap_netlink_recv);
/**
* cap_capable - Determine whether a task has a particular effective capability
* @tsk: The task to query
+ * @cred: The credentials to use
* @cap: The capability to check for
* @audit: Whether to write an audit message or not
*
* 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_capable() cannot be used like the kernel's capable()
- * function. That is, it has the reverse semantics: cap_capable() returns 0
- * when a task has a capability, but the kernel's capable() returns 1 for this
- * case.
+ * 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(struct task_struct *tsk, int cap, int audit)
+int cap_capable(struct task_struct *tsk, const struct cred *cred, int cap,
+ int audit)
{
- __u32 cap_raised;
-
- /* Derived from include/linux/sched.h:capable. */
- rcu_read_lock();
- cap_raised = cap_raised(__task_cred(tsk)->cap_effective, cap);
- rcu_read_unlock();
- return cap_raised ? 0 : -EPERM;
+ return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
}
/**
@@ -160,7 +156,8 @@ static inline int cap_inh_is_capped(void)
/* they are so limited unless the current task has the CAP_SETPCAP
* capability
*/
- if (cap_capable(current, CAP_SETPCAP, SECURITY_CAP_AUDIT) == 0)
+ if (cap_capable(current, current_cred(), CAP_SETPCAP,
+ SECURITY_CAP_AUDIT) == 0)
return 0;
#endif
return 1;
@@ -869,7 +866,8 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
& (new->securebits ^ arg2)) /*[1]*/
|| ((new->securebits & SECURE_ALL_LOCKS & ~arg2)) /*[2]*/
|| (arg2 & ~(SECURE_ALL_LOCKS | SECURE_ALL_BITS)) /*[3]*/
- || (cap_capable(current, CAP_SETPCAP, SECURITY_CAP_AUDIT) != 0) /*[4]*/
+ || (cap_capable(current, current_cred(), CAP_SETPCAP,
+ SECURITY_CAP_AUDIT) != 0) /*[4]*/
/*
* [1] no changing of bits that are locked
* [2] no unlocking of locks
@@ -950,7 +948,8 @@ int cap_vm_enough_memory(struct mm_struct *mm, long pages)
{
int cap_sys_admin = 0;
- if (cap_capable(current, CAP_SYS_ADMIN, SECURITY_CAP_NOAUDIT) == 0)
+ if (cap_capable(current, current_cred(), CAP_SYS_ADMIN,
+ SECURITY_CAP_NOAUDIT) == 0)
cap_sys_admin = 1;
return __vm_enough_memory(mm, pages, cap_sys_admin);
}
diff --git a/security/security.c b/security/security.c
index d85dbb37c97..a02f243f09c 100644
--- a/security/security.c
+++ b/security/security.c
@@ -154,14 +154,32 @@ int security_capset(struct cred *new, const struct cred *old,
effective, inheritable, permitted);
}
-int security_capable(struct task_struct *tsk, int cap)
+int security_capable(int cap)
{
- return security_ops->capable(tsk, cap, SECURITY_CAP_AUDIT);
+ return security_ops->capable(current, current_cred(), cap,
+ SECURITY_CAP_AUDIT);
}
-int security_capable_noaudit(struct task_struct *tsk, int cap)
+int security_real_capable(struct task_struct *tsk, int cap)
{
- return security_ops->capable(tsk, cap, SECURITY_CAP_NOAUDIT);
+ const struct cred *cred;
+ int ret;
+
+ cred = get_task_cred(tsk);
+ ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_AUDIT);
+ put_cred(cred);
+ return ret;
+}
+
+int security_real_capable_noaudit(struct task_struct *tsk, int cap)
+{
+ const struct cred *cred;
+ int ret;
+
+ cred = get_task_cred(tsk);
+ ret = security_ops->capable(tsk, cred, cap, SECURITY_CAP_NOAUDIT);
+ put_cred(cred);
+ return ret;
}
int security_acct(struct file *file)
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index df30a7555d8..00815973d41 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -1433,12 +1433,13 @@ static int current_has_perm(const struct task_struct *tsk,
/* Check whether a task is allowed to use a capability. */
static int task_has_capability(struct task_struct *tsk,
+ const struct cred *cred,
int cap, int audit)
{
struct avc_audit_data ad;
struct av_decision avd;
u16 sclass;
- u32 sid = task_sid(tsk);
+ u32 sid = cred_sid(cred);
u32 av = CAP_TO_MASK(cap);
int rc;
@@ -1865,15 +1866,16 @@ static int selinux_capset(struct cred *new, const struct cred *old,
return cred_has_perm(old, new, PROCESS__SETCAP);
}
-static int selinux_capable(struct task_struct *tsk, int cap, int audit)
+static int selinux_capable(struct task_struct *tsk, const struct cred *cred,
+ int cap, int audit)
{
int rc;
- rc = secondary_ops->capable(tsk, cap, audit);
+ rc = secondary_ops->capable(tsk, cred, cap, audit);
if (rc)
return rc;
- return task_has_capability(tsk, cap, audit);
+ return task_has_capability(tsk, cred, cap, audit);
}
static int selinux_sysctl_get_sid(ctl_table *table, u16 tclass, u32 *sid)
@@ -2037,7 +2039,8 @@ static int selinux_vm_enough_memory(struct mm_struct *mm, long pages)
{
int rc, cap_sys_admin = 0;
- rc = selinux_capable(current, CAP_SYS_ADMIN, SECURITY_CAP_NOAUDIT);
+ rc = selinux_capable(current, current_cred(), CAP_SYS_ADMIN,
+ SECURITY_CAP_NOAUDIT);
if (rc == 0)
cap_sys_admin = 1;
@@ -2880,7 +2883,8 @@ static int selinux_inode_getsecurity(const struct inode *inode, const char *name
* and lack of permission just means that we fall back to the
* in-core context value, not a denial.
*/
- error = selinux_capable(current, CAP_MAC_ADMIN, SECURITY_CAP_NOAUDIT);
+ error = selinux_capable(current, current_cred(), CAP_MAC_ADMIN,
+ SECURITY_CAP_NOAUDIT);
if (!error)
error = security_sid_to_context_force(isec->sid, &context,
&size);