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Subject[PATCH 3/4] security: capabilities patch (version 0.4.3), part 3/4: introduce new capabilities

Introduce six new "regular" (=on-by-default) capabilities:

* CAP_REG_FORK, CAP_REG_OPEN, CAP_REG_EXEC allow access to the
fork(), open() and exec() syscalls,

* CAP_REG_SXID allows privilege gain on suid/sgid exec,

* CAP_REG_WRITE controls any write-access to the filesystem,

* CAP_REG_PTRACE allows ptrace().

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 | 7 +++++--
fs/namei.c | 2 +-
fs/open.c | 26 ++++++++++++++++++++------
fs/xattr.c | 3 ++-
include/linux/capability.h | 23 +++++++++++++++++++++++
kernel/fork.c | 2 ++
kernel/ptrace.c | 2 ++
7 files changed, 55 insertions(+), 10 deletions(-)

diff --git a/fs/exec.c b/fs/exec.c
index e4d0a2c..1cb5e34 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -930,7 +930,7 @@ int prepare_binprm(struct linux_binprm *

if(!(bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)) {
/* Set-uid? */
- if (mode & S_ISUID) {
+ if (mode & S_ISUID && capable(CAP_REG_SXID)) {
bprm->is_suid = 1;
current->personality &= ~PER_CLEAR_ON_SETID;
bprm->e_uid = inode->i_uid;
@@ -942,7 +942,8 @@ int prepare_binprm(struct linux_binprm *
* is a candidate for mandatory locking, not a setgid
* executable.
*/
- if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)) {
+ if ((mode & (S_ISGID | S_IXGRP)) == (S_ISGID | S_IXGRP)
+ && capable(CAP_REG_SXID)) {
bprm->is_sgid = 1;
current->personality &= ~PER_CLEAR_ON_SETID;
bprm->e_gid = inode->i_gid;
@@ -1137,6 +1138,8 @@ int do_execve(char * filename,
int retval;
int i;

+ if (!capable(CAP_REG_EXEC))
+ return -EPERM;
retval = -ENOMEM;
bprm = kzalloc(sizeof(*bprm), GFP_KERNEL);
if (!bprm)
diff --git a/fs/namei.c b/fs/namei.c
index 432d6bc..69a3bae 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -242,7 +242,7 @@ int permission(struct inode *inode, int
/*
* Nobody gets write access to an immutable file.
*/
- if (IS_IMMUTABLE(inode))
+ if (IS_IMMUTABLE(inode) || !capable(CAP_REG_WRITE))
return -EACCES;
}

diff --git a/fs/open.c b/fs/open.c
index e58a525..77a12ba 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -253,7 +253,7 @@ static long do_sys_truncate(const char _
goto dput_and_out;

error = -EPERM;
- if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
+ if (IS_IMMUTABLE(inode) || IS_APPEND(inode) || !capable(CAP_REG_WRITE))
goto dput_and_out;

/*
@@ -382,6 +382,10 @@ asmlinkage long sys_utime(char __user *
if (IS_RDONLY(inode))
goto dput_and_out;

+ error = -EPERM;
+ if (!capable(CAP_REG_WRITE))
+ goto dput_and_out;
+
/* Don't worry, the checks are done in inode_change_ok() */
newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
if (times) {
@@ -439,6 +443,10 @@ long do_utimes(int dfd, char __user *fil
if (IS_RDONLY(inode))
goto dput_and_out;

+ error = -EPERM;
+ if (!capable(CAP_REG_WRITE))
+ goto dput_and_out;
+
/* Don't worry, the checks are done in inode_change_ok() */
newattrs.ia_valid = ATTR_CTIME | ATTR_MTIME | ATTR_ATIME;
if (times) {
@@ -640,7 +648,7 @@ asmlinkage long sys_fchmod(unsigned int
if (IS_RDONLY(inode))
goto out_putf;
err = -EPERM;
- if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
+ if (IS_IMMUTABLE(inode) || IS_APPEND(inode) || !capable(CAP_REG_WRITE))
goto out_putf;
mutex_lock(&inode->i_mutex);
if (mode == (mode_t) -1)
@@ -674,7 +682,7 @@ asmlinkage long sys_fchmodat(int dfd, co
goto dput_and_out;

error = -EPERM;
- if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
+ if (IS_IMMUTABLE(inode) || IS_APPEND(inode) || !capable(CAP_REG_WRITE))
goto dput_and_out;

mutex_lock(&inode->i_mutex);
@@ -711,7 +719,7 @@ static int chown_common(struct dentry *
if (IS_RDONLY(inode))
goto out;
error = -EPERM;
- if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
+ if (IS_IMMUTABLE(inode) || IS_APPEND(inode) || !capable(CAP_REG_WRITE))
goto out;
newattrs.ia_valid = ATTR_CTIME;
if (user != (uid_t) -1) {
@@ -1105,7 +1113,10 @@ asmlinkage long sys_open(const char __us
if (force_o_largefile())
flags |= O_LARGEFILE;

- ret = do_sys_open(AT_FDCWD, filename, flags, mode);
+ if (capable(CAP_REG_OPEN))
+ ret = do_sys_open(AT_FDCWD, filename, flags, mode);
+ else
+ ret = -EPERM;
/* avoid REGPARM breakage on x86: */
prevent_tail_call(ret);
return ret;
@@ -1120,7 +1131,10 @@ asmlinkage long sys_openat(int dfd, cons
if (force_o_largefile())
flags |= O_LARGEFILE;

- ret = do_sys_open(dfd, filename, flags, mode);
+ if (capable(CAP_REG_OPEN))
+ ret = do_sys_open(dfd, filename, flags, mode);
+ else
+ ret = -EPERM;
/* avoid REGPARM breakage on x86: */
prevent_tail_call(ret);
return ret;
diff --git a/fs/xattr.c b/fs/xattr.c
index c32f15b..33b70ce 100644
--- a/fs/xattr.c
+++ b/fs/xattr.c
@@ -35,7 +35,8 @@ xattr_permission(struct inode *inode, co
if (mask & MAY_WRITE) {
if (IS_RDONLY(inode))
return -EROFS;
- if (IS_IMMUTABLE(inode) || IS_APPEND(inode))
+ if (IS_IMMUTABLE(inode) || IS_APPEND(inode)
+ || !capable(CAP_REG_WRITE))
return -EPERM;
}

diff --git a/include/linux/capability.h b/include/linux/capability.h
index aa00b60..efc268e 100644
--- a/include/linux/capability.h
+++ b/include/linux/capability.h
@@ -295,6 +295,29 @@ #define CAP_AUDIT_WRITE 29

#define CAP_AUDIT_CONTROL 30

+
+/**
+ ** Regular capabilities (normally possessed by all processes).
+ **/
+
+/* Can fork() */
+#define CAP_REG_FORK 32
+
+/* Can open() */
+#define CAP_REG_OPEN 33
+
+/* Can exec() */
+#define CAP_REG_EXEC 34
+
+/* Might gain permissions on exec() */
+#define CAP_REG_SXID 35
+
+/* Perform write access to the filesystem */
+#define CAP_REG_WRITE 36
+
+/* Can use ptrace() */
+#define CAP_REG_PTRACE 37
+
#ifdef __KERNEL__
/*
* Bounding set
diff --git a/kernel/fork.c b/kernel/fork.c
index f9b014e..20f559f 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1347,6 +1347,8 @@ long do_fork(unsigned long clone_flags,
struct pid *pid = alloc_pid();
long nr;

+ if (!capable(CAP_REG_FORK))
+ return -EPERM;
if (!pid)
return -EAGAIN;
nr = pid->nr;
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 9a111f7..093307d 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -132,6 +132,8 @@ static int may_attach(struct task_struct
/* Don't let security modules deny introspection */
if (task == current)
return 0;
+ if (!capable(CAP_REG_PTRACE))
+ return -EPERM;
if (((current->uid != task->euid) ||
(current->uid != task->suid) ||
(current->uid != task->uid) ||
-
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