lkml.org 
[lkml]   [2009]   [Dec]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    From
    Date
    Subject[RFC][PATCH v2] Unprivileged: Disable raising of privileges

    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@xmission.com>
    ---
    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(&current->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


    \
     
     \ /
      Last update: 2009-12-30 13:53    [W:2.652 / U:0.100 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site