lkml.org 
[lkml]   [2006]   [Sep]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH 2/4] security: capabilities patch (version 0.4.3), part 2/4: change inheritance semantics

Make capabilities inheritable by default. The following remarks
apply:

* executables are assumed by default to have a full set of
"inheritable" (allowed) and "effective" capabilities,

* w.r.t. capabilities(7)-documented behavior, inheritance of the
effective bits is changed (use P(eff) rather than F(eff) in half
of the formula),

* also, inheritance of the inheritable set is based on the new
permitted set rather than on the old inheritable.

See <URL: http://www.madore.org/~david/linux/newcaps/ > for more
detailed explanations.
Signed-off-by: David A. Madore <david.madore@ens.fr>

---
fs/exec.c | 4 +++
include/linux/binfmts.h | 1 +
kernel/capability.c | 2 +
security/commoncap.c | 69 ++++++++++++++++++++++++++++-------------------
4 files changed, 47 insertions(+), 29 deletions(-)
diff --git a/fs/exec.c b/fs/exec.c
index 54135df..e4d0a2c 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -925,10 +925,13 @@ int prepare_binprm(struct linux_binprm *

bprm->e_uid = current->euid;
bprm->e_gid = current->egid;
+ bprm->is_suid = 0;
+ bprm->is_sgid = 0;

if(!(bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)) {
/* Set-uid? */
if (mode & S_ISUID) {
+ bprm->is_suid = 1;
current->personality &= ~PER_CLEAR_ON_SETID;
bprm->e_uid = inode->i_uid;
}
@@ -940,6 +943,7 @@ int prepare_binprm(struct linux_binprm *
* executable.
*/
if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
+ bprm->is_sgid = 1;
current->personality &= ~PER_CLEAR_ON_SETID;
bprm->e_gid = inode->i_gid;
}
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index c1e82c5..c7fb183 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -29,6 +29,7 @@ struct linux_binprm{
struct file * file;
int e_uid, e_gid;
kernel_cap_t cap_inheritable, cap_permitted, cap_effective;
+ char is_suid, is_sgid;
void *security;
int argc, envc;
char * filename; /* Name of binary as seen by procps */
diff --git a/kernel/capability.c b/kernel/capability.c
index 32b2521..2bb802a 100644
--- a/kernel/capability.c
+++ b/kernel/capability.c
@@ -15,7 +15,7 @@ #include <linux/syscalls.h>
#include <asm/uaccess.h>

unsigned securebits = SECUREBITS_DEFAULT; /* systemwide security settings */
-kernel_cap_t cap_bset = CAP_INIT_EFF_SET;
+kernel_cap_t cap_bset = CAP_INIT_INH_SET;

EXPORT_SYMBOL(securebits);
EXPORT_SYMBOL(cap_bset);
diff --git a/security/commoncap.c b/security/commoncap.c
index 91dc53d..3f90ae8 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -97,6 +97,8 @@ int cap_capset_check (struct task_struct
if (!cap_issubset (*effective, *permitted)) {
return -EPERM;
}
+ /* we allow Inheritable not to be a subset of Permitted:
+ * cap_capset_set will intersect them anyway */

return 0;
}
@@ -105,7 +107,7 @@ void cap_capset_set (struct task_struct
kernel_cap_t *inheritable, kernel_cap_t *permitted)
{
target->cap_effective = *effective;
- target->cap_inheritable = *inheritable;
+ target->cap_inheritable = cap_intersect (*permitted, *inheritable);
target->cap_permitted = *permitted;
}

@@ -114,25 +116,20 @@ int cap_bprm_set_security (struct linux_
/* Copied from fs/exec.c:prepare_binprm. */

/* We don't have VFS support for capabilities yet */
- cap_clear (bprm->cap_inheritable);
+ cap_set_full (bprm->cap_inheritable);
cap_clear (bprm->cap_permitted);
- cap_clear (bprm->cap_effective);
+ cap_set_full (bprm->cap_effective);

/* 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 (bprm->e_uid == 0 || current->uid == 0) {
+ if (bprm->is_suid && bprm->e_uid == 0) {
cap_set_full (bprm->cap_inheritable);
cap_set_full (bprm->cap_permitted);
- }
- if (bprm->e_uid == 0)
cap_set_full (bprm->cap_effective);
+ }
}
return 0;
}
@@ -140,13 +137,25 @@ int cap_bprm_set_security (struct linux_
void cap_bprm_apply_creds (struct linux_binprm *bprm, int unsafe)
{
/* Derived from fs/exec.c:compute_creds. */
- kernel_cap_t new_permitted, working;
+ kernel_cap_t new_permitted, new_effective, working;
+ uid_t old_ruid, old_euid, old_suid;

+ /* P'(per) = (P(inh) & F(inh)) | (F(per) & bset) */
new_permitted = cap_intersect (bprm->cap_permitted, cap_bset);
working = cap_intersect (bprm->cap_inheritable,
current->cap_inheritable);
new_permitted = cap_combine (new_permitted, working);

+ /* P'(eff) = (P(inh) & P(eff) & F(inh)) | (F(per) & F(eff) & bset) */
+ new_effective = cap_intersect (bprm->cap_permitted, bprm->cap_effective);
+ new_effective = cap_intersect (new_effective, cap_bset);
+ working = cap_intersect (bprm->cap_inheritable,
+ current->cap_effective);
+ working = cap_intersect (working, current->cap_inheritable);
+ new_effective = cap_combine (new_effective, working);
+
+ /* P'(inh) = P'(per) */
+
if (bprm->e_uid != current->uid || bprm->e_gid != current->gid ||
!cap_issubset (new_permitted, current->cap_permitted)) {
current->mm->dumpable = suid_dumpable;
@@ -159,36 +168,37 @@ void cap_bprm_apply_creds (struct linux_
if (!capable (CAP_SETPCAP)) {
new_permitted = cap_intersect (new_permitted,
current->cap_permitted);
+ new_effective = cap_intersect (new_permitted,
+ new_effective);
}
}
}

+ old_ruid = current->uid;
+ old_euid = current->euid;
+ old_suid = current->suid;
current->suid = current->euid = current->fsuid = bprm->e_uid;
current->sgid = current->egid = current->fsgid = bprm->e_gid;

- /* For init, we want to retain the capabilities set
- * in the init_task struct. Thus we skip the usual
- * capability rules */
- if (current->pid != 1) {
- current->cap_permitted = new_permitted;
- current->cap_effective =
- cap_intersect (new_permitted, bprm->cap_effective);
- }
-
- /* AUD: Audit candidate if current->cap_effective is set */
+ current->cap_permitted = new_permitted;
+ current->cap_effective = new_effective;
+ current->cap_inheritable = new_permitted;

current->keep_capabilities = 0;
+ /* Make sure we drop capabilities if required by suid. */
+ cap_task_post_setuid (old_ruid, old_euid, old_suid, LSM_SETID_RES);
+
+ /* AUD: Audit candidate if current->cap_effective is set */
}

int cap_bprm_secureexec (struct linux_binprm *bprm)
{
/* If/when this module is enhanced to incorporate capability
bits on files, the test below should be extended to also perform a
- test between the old and new capability sets. For now,
- it simply preserves the legacy decision algorithm used by
- the old userland. */
- return (current->euid != current->uid ||
- current->egid != current->gid);
+ test between the old and new capability sets. */
+ return ((bprm->is_suid || bprm->is_sgid)
+ && !cap_issubset (bprm->cap_permitted,
+ current->cap_permitted));
}

int cap_inode_setxattr(struct dentry *dentry, char *name, void *value,
@@ -253,12 +263,15 @@ static inline void cap_emulate_setxuid (
= cap_intersect (current->cap_effective,
CAP_REGULAR_SET);
}
+ current->cap_inheritable
+ = cap_intersect (current->cap_inheritable,
+ CAP_REGULAR_SET);
}
- if (old_euid == 0 && current->euid != 0) {
+ if (old_euid == 0 && current->euid != 0 && !current->keep_capabilities) {
current->cap_effective = cap_intersect (current->cap_effective,
CAP_REGULAR_SET);
}
- if (old_euid != 0 && current->euid == 0) {
+ if (old_euid != 0 && current->euid == 0 && !current->keep_capabilities) {
current->cap_effective = current->cap_permitted;
}
}
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
\
 
 \ /
  Last update: 2006-09-08 20:31    [W:0.553 / U:0.024 seconds]
©2003-2011 Jasper Spaans. Advertise on this site