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authorAndrew G. Morgan <morgan@kernel.org>2008-07-23 21:28:24 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2008-07-24 10:47:22 -0700
commit5459c164f0591ee75ed0203bb8f3817f25948e2f (patch)
tree7b17a0cbadfc487d7311b7f5a41779ff33d6fe7f /security/commoncap.c
parent78ecba081224a2db5876b6b81cfed0b78f58adc7 (diff)
downloadlinux-linaro-stable-5459c164f0591ee75ed0203bb8f3817f25948e2f.tar.gz
security: protect legacy applications from executing with insufficient privilege
When cap_bset suppresses some of the forced (fP) capabilities of a file, it is generally only safe to execute the program if it understands how to recognize it doesn't have enough privilege to work correctly. For legacy applications (fE!=0), which have no non-destructive way to determine that they are missing privilege, we fail to execute (EPERM) any executable that requires fP capabilities, but would otherwise get pP' < fP. This is a fail-safe permission check. For some discussion of why it is problematic for (legacy) privileged applications to run with less than the set of capabilities requested for them, see: http://userweb.kernel.org/~morgan/sendmail-capabilities-war-story.html With this iteration of this support, we do not include setuid-0 based privilege protection from the bounding set. That is, the admin can still (ab)use the bounding set to suppress the privileges of a setuid-0 program. [akpm@linux-foundation.org: coding-style fixes] [akpm@linux-foundation.org: cleanup] Signed-off-by: Andrew G. Morgan <morgan@kernel.org> Acked-by: Serge Hallyn <serue@us.ibm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'security/commoncap.c')
-rw-r--r--security/commoncap.c108
1 files changed, 59 insertions, 49 deletions
diff --git a/security/commoncap.c b/security/commoncap.c
index 0b6537a3672d..4afbece37a08 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -162,8 +162,7 @@ void cap_capset_set (struct task_struct *target, kernel_cap_t *effective,
static inline void bprm_clear_caps(struct linux_binprm *bprm)
{
- cap_clear(bprm->cap_inheritable);
- cap_clear(bprm->cap_permitted);
+ cap_clear(bprm->cap_post_exec_permitted);
bprm->cap_effective = false;
}
@@ -198,6 +197,7 @@ static inline int cap_from_disk(struct vfs_cap_data *caps,
{
__u32 magic_etc;
unsigned tocopy, i;
+ int ret;
if (size < sizeof(magic_etc))
return -EINVAL;
@@ -225,19 +225,40 @@ static inline int cap_from_disk(struct vfs_cap_data *caps,
bprm->cap_effective = false;
}
- for (i = 0; i < tocopy; ++i) {
- bprm->cap_permitted.cap[i] =
- le32_to_cpu(caps->data[i].permitted);
- bprm->cap_inheritable.cap[i] =
- le32_to_cpu(caps->data[i].inheritable);
- }
- while (i < VFS_CAP_U32) {
- bprm->cap_permitted.cap[i] = 0;
- bprm->cap_inheritable.cap[i] = 0;
- i++;
+ ret = 0;
+
+ CAP_FOR_EACH_U32(i) {
+ __u32 value_cpu;
+
+ if (i >= tocopy) {
+ /*
+ * Legacy capability sets have no upper bits
+ */
+ bprm->cap_post_exec_permitted.cap[i] = 0;
+ continue;
+ }
+ /*
+ * pP' = (X & fP) | (pI & fI)
+ */
+ value_cpu = le32_to_cpu(caps->data[i].permitted);
+ bprm->cap_post_exec_permitted.cap[i] =
+ (current->cap_bset.cap[i] & value_cpu) |
+ (current->cap_inheritable.cap[i] &
+ le32_to_cpu(caps->data[i].inheritable));
+ if (value_cpu & ~bprm->cap_post_exec_permitted.cap[i]) {
+ /*
+ * insufficient to execute correctly
+ */
+ ret = -EPERM;
+ }
}
- return 0;
+ /*
+ * For legacy apps, with no internal support for recognizing they
+ * do not have enough capabilities, we return an error if they are
+ * missing some "forced" (aka file-permitted) capabilities.
+ */
+ return bprm->cap_effective ? ret : 0;
}
/* Locate any VFS capabilities: */
@@ -269,9 +290,9 @@ static int get_file_caps(struct linux_binprm *bprm)
goto out;
rc = cap_from_disk(&vcaps, bprm, rc);
- if (rc)
+ if (rc == -EINVAL)
printk(KERN_NOTICE "%s: cap_from_disk returned %d for %s\n",
- __func__, rc, bprm->filename);
+ __func__, rc, bprm->filename);
out:
dput(dentry);
@@ -304,25 +325,24 @@ int cap_bprm_set_security (struct linux_binprm *bprm)
int ret;
ret = get_file_caps(bprm);
- if (ret)
- printk(KERN_NOTICE "%s: get_file_caps returned %d for %s\n",
- __func__, ret, bprm->filename);
-
- /* To support inheritance of root-permissions and suid-root
- * executables under compatibility mode, we raise all three
- * capability sets for the file.
- *
- * If only the real uid is 0, we only raise the inheritable
- * and permitted sets of the executable file.
- */
- if (!issecure (SECURE_NOROOT)) {
+ if (!issecure(SECURE_NOROOT)) {
+ /*
+ * To support inheritance of root-permissions and suid-root
+ * executables under compatibility mode, we override the
+ * capability sets for the file.
+ *
+ * If only the real uid is 0, we do not set the effective
+ * bit.
+ */
if (bprm->e_uid == 0 || current->uid == 0) {
- cap_set_full (bprm->cap_inheritable);
- cap_set_full (bprm->cap_permitted);
+ /* pP' = (cap_bset & ~0) | (pI & ~0) */
+ bprm->cap_post_exec_permitted = cap_combine(
+ current->cap_bset, current->cap_inheritable
+ );
+ bprm->cap_effective = (bprm->e_uid == 0);
+ ret = 0;
}
- if (bprm->e_uid == 0)
- bprm->cap_effective = true;
}
return ret;
@@ -330,17 +350,9 @@ int cap_bprm_set_security (struct linux_binprm *bprm)
void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
{
- /* Derived from fs/exec.c:compute_creds. */
- kernel_cap_t new_permitted, working;
-
- new_permitted = cap_intersect(bprm->cap_permitted,
- current->cap_bset);
- working = cap_intersect(bprm->cap_inheritable,
- current->cap_inheritable);
- new_permitted = cap_combine(new_permitted, working);
-
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
- !cap_issubset (new_permitted, current->cap_permitted)) {
+ !cap_issubset(bprm->cap_post_exec_permitted,
+ current->cap_permitted)) {
set_dumpable(current->mm, suid_dumpable);
current->pdeath_signal = 0;
@@ -350,9 +362,9 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
bprm->e_gid = current->gid;
}
if (cap_limit_ptraced_target()) {
- new_permitted =
- cap_intersect(new_permitted,
- current->cap_permitted);
+ bprm->cap_post_exec_permitted = cap_intersect(
+ bprm->cap_post_exec_permitted,
+ current->cap_permitted);
}
}
}
@@ -364,9 +376,9 @@ void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
* in the init_task struct. Thus we skip the usual
* capability rules */
if (!is_global_init(current)) {
- current->cap_permitted = new_permitted;
+ current->cap_permitted = bprm->cap_post_exec_permitted;
if (bprm->cap_effective)
- current->cap_effective = new_permitted;
+ current->cap_effective = bprm->cap_post_exec_permitted;
else
cap_clear(current->cap_effective);
}
@@ -381,9 +393,7 @@ int cap_bprm_secureexec (struct linux_binprm *bprm)
if (current->uid != 0) {
if (bprm->cap_effective)
return 1;
- if (!cap_isclear(bprm->cap_permitted))
- return 1;
- if (!cap_isclear(bprm->cap_inheritable))
+ if (!cap_isclear(bprm->cap_post_exec_permitted))
return 1;
}