[RFC][PATCH v2] Unprivileged: Disable raising of privileges
From: Eric W. Biederman
Date: Wed Dec 30 2009 - 07:49:56 EST
If we can know that a process will never raise
it's priveleges we can enable a lot of features
that otherwise would be unsafe, because they
could break assumptions of existing suid executables.
To allow this to be used as a sand boxing feature
also disable ptracing other executables without
this new restriction.
For the moment I have used a per thread flag because
we are out of per process flags.
To ensure all descendants get this flag I rely on
the default copying of procss structures.
Added bprm->nosuid to make remove the need to add
duplicate error prone checks. This ensures that
the disabling of suid executables is exactly the
same as MNT_NOSUID.
Signed-off-by: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
---
arch/x86/include/asm/thread_info.h | 2 ++
fs/exec.c | 6 ++++--
include/linux/binfmts.h | 1 +
include/linux/prctl.h | 2 ++
kernel/ptrace.c | 4 ++++
kernel/sys.c | 16 ++++++++++++++++
security/commoncap.c | 14 +++++++++++++-
security/selinux/hooks.c | 2 +-
8 files changed, 43 insertions(+), 4 deletions(-)
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 375c917..e716203 100644
--- a/arch/x86/include/asm/thread_info.h
+++ b/arch/x86/include/asm/thread_info.h
@@ -82,6 +82,7 @@ struct thread_info {
#define TIF_SYSCALL_EMU 6 /* syscall emulation active */
#define TIF_SYSCALL_AUDIT 7 /* syscall auditing active */
#define TIF_SECCOMP 8 /* secure computing */
+#define TIF_NOSUID 9 /* suid exec permanently disabled */
#define TIF_MCE_NOTIFY 10 /* notify userspace of an MCE */
#define TIF_USER_RETURN_NOTIFY 11 /* notify kernel of userspace return */
#define TIF_NOTSC 16 /* TSC is not accessible in userland */
@@ -107,6 +108,7 @@ struct thread_info {
#define _TIF_SYSCALL_EMU (1 << TIF_SYSCALL_EMU)
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
#define _TIF_SECCOMP (1 << TIF_SECCOMP)
+#define _TIF_NOSUID (1 << TIF_NOSUID)
#define _TIF_MCE_NOTIFY (1 << TIF_MCE_NOTIFY)
#define _TIF_USER_RETURN_NOTIFY (1 << TIF_USER_RETURN_NOTIFY)
#define _TIF_NOTSC (1 << TIF_NOTSC)
diff --git a/fs/exec.c b/fs/exec.c
index 632b02e..5cba5ac 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1131,8 +1131,10 @@ int prepare_binprm(struct linux_binprm *bprm)
/* clear any previous set[ug]id data from a previous binary */
bprm->cred->euid = current_euid();
bprm->cred->egid = current_egid();
-
- if (!(bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)) {
+ bprm->nosuid =
+ (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID) ||
+ test_tsk_thread_flag(current, TIF_NOSUID);
+ if (bprm->nosuid) {
/* Set-uid? */
if (mode & S_ISUID) {
bprm->per_clear |= PER_CLEAR_ON_SETID;
diff --git a/include/linux/binfmts.h b/include/linux/binfmts.h
index cd4349b..c3b5a30 100644
--- a/include/linux/binfmts.h
+++ b/include/linux/binfmts.h
@@ -44,6 +44,7 @@ struct linux_binprm{
#ifdef __alpha__
unsigned int taso:1;
#endif
+ unsigned int nosuid:1; /* True if suid bits are ignored */
unsigned int recursion_depth;
struct file * file;
struct cred *cred; /* new credentials */
diff --git a/include/linux/prctl.h b/include/linux/prctl.h
index a3baeb2..acb3516 100644
--- a/include/linux/prctl.h
+++ b/include/linux/prctl.h
@@ -102,4 +102,6 @@
#define PR_MCE_KILL_GET 34
+#define PR_SET_NOSUID 35
+
#endif /* _LINUX_PRCTL_H */
diff --git a/kernel/ptrace.c b/kernel/ptrace.c
index 23bd09c..b91040c 100644
--- a/kernel/ptrace.c
+++ b/kernel/ptrace.c
@@ -152,6 +152,10 @@ int __ptrace_may_access(struct task_struct *task, unsigned int mode)
if (!dumpable && !capable(CAP_SYS_PTRACE))
return -EPERM;
+ if (test_tsk_thread_flag(current, TIF_NOSUID) &&
+ !test_tsk_thread_flag(task, TIF_NOSUID))
+ return -EPERM;
+
return security_ptrace_access_check(task, mode);
}
diff --git a/kernel/sys.c b/kernel/sys.c
index 26a6b73..1d1902a 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1578,6 +1578,22 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
else
error = PR_MCE_KILL_DEFAULT;
break;
+ case PR_SET_NOSUID:
+ {
+ const struct cred *cred = current->cred;
+ error = -EINVAL;
+ if ( (cred->uid != cred->suid) ||
+ (cred->uid != cred->euid) ||
+ (cred->uid != cred->fsuid) ||
+ (cred->gid != cred->sgid) ||
+ (cred->gid != cred->egid) ||
+ (cred->gid != cred->fsgid) ||
+ (atomic_read(¤t->signal->count) != 1))
+ break;
+ error = 0;
+ set_tsk_thread_flag(current, TIF_NOSUID);
+ break;
+ }
default:
error = -EINVAL;
break;
diff --git a/security/commoncap.c b/security/commoncap.c
index f800fdb..28ab286 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -389,7 +389,7 @@ static int get_file_caps(struct linux_binprm *bprm, bool *effective)
if (!file_caps_enabled)
return 0;
- if (bprm->file->f_vfsmnt->mnt_flags & MNT_NOSUID)
+ if (bprm->nosuid)
return 0;
dentry = dget(bprm->file->f_dentry);
@@ -869,6 +869,18 @@ int cap_task_prctl(int option, unsigned long arg2, unsigned long arg3,
new->securebits &= ~issecure_mask(SECURE_KEEP_CAPS);
goto changed;
+ case PR_SET_NOSUID:
+ {
+ const struct cred *cred = current->cred;
+ error = -EINVAL;
+ /* Perform the capabilities checks */
+ if (!cap_isclear(cred->cap_permitted) ||
+ !cap_isclear(cred->cap_effective))
+ goto error;
+ /* Have the default perform the rest of the work. */
+ error = -ENOSYS;
+ goto error;
+ }
default:
/* No functionality available - continue with default */
error = -ENOSYS;
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 7a374c2..d14cd24 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2147,7 +2147,7 @@ static int selinux_bprm_set_creds(struct linux_binprm *bprm)
COMMON_AUDIT_DATA_INIT(&ad, FS);
ad.u.fs.path = bprm->file->f_path;
- if (bprm->file->f_path.mnt->mnt_flags & MNT_NOSUID)
+ if (bprm->nosid)
new_tsec->sid = old_tsec->sid;
if (new_tsec->sid == old_tsec->sid) {
--
1.6.5.2.143.g8cc62
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/