# cap_get_proc

## NAME



           cap_get_proc, cap_set_proc, capgetp, cap_get_bound,
           cap_drop_bound, cap_get_ambient, cap_set_ambient,
           cap_reset_ambient, cap_get_secbits, cap_set_secbits, cap_get_mode,
           cap_set_mode, cap_mode_name, cap_get_pid, cap_setuid, cap_prctl,
           cap_prctlw, cap_setgroups - capability manipulation on processes
    


## SYNOPSIS



           #include <sys/capability.h>
    
           cap_t cap_get_proc(void);
           int cap_set_proc(cap_t cap_p);
    
           int cap_get_bound(cap_value_t cap);
           CAP_IS_SUPPORTED(cap_value_t cap);
    
           int cap_drop_bound(cap_value_t cap);
           int cap_get_ambient(cap_value_t cap);
           int cap_set_ambient(cap_value_t cap, cap_flag_value_t value);
           int cap_reset_ambient(void);
           CAP_AMBIENT_SUPPORTED();
    
           unsigned cap_get_secbits(void);
           int cap_set_secbits(unsigned bits);
           cap_mode_t cap_get_mode(void);
           const char *cap_mode_name(cap_mode_t mode);
           int cap_prctl(long int pr_cmd, long int arg1, long int arg2,
                      long int arg3, long int arg4, long int arg5);
           int cap_prctlw(long int pr_cmd, long int arg1, long int arg2,
                       long int arg3, long int arg4, long int arg5);
           int cap_set_mode(cap_mode_t mode);
    
           #include <sys/types.h>
    
           cap_t cap_get_pid(pid_t pid);
           int cap_setuid(uid_t uid);
           int cap_setgroups(gid_t gid, size_t ngroups, const gid_t groups);
    
           Link with _-lcap_.
    


## DESCRIPTION



           **cap_get_proc**() allocates a capability state in working storage,
           sets its state to that of the calling process, and returns a
           pointer to this newly created capability state.  The caller should
           free any releasable memory, when the capability state in working
           storage is no longer required, by calling **cap_free**() with the
           _cap_t_ as an argument.
    
           **cap_set_proc**() sets the values for all capability flags for all
           capabilities to the capability state identified by _cap_p_.  The new
           capability state of the process will be completely determined by
           the contents of _cap_p_ upon successful return from this function.
           If any flag in _cap_p_ is set for any capability not currently
           permitted for the calling process, the function will fail, and the
           capability state of the process will remain unchanged.
    
           **cap_get_pid**() returns a _cap_t_ , see cap_init(3), with the process
           capabilities of the process known to the caller as _pid_.  If _pid_ is
           0, then the calling process's capabilities are returned.  This
           information can also be obtained from the _/proc/ <pid>/status_ file.
           (The entries in that file can be translated with the **capsh**
           **--decode=**_XXX_ command line.) When the caller is operating within a
           (**CLONE_NEWPID**) namespace, the numerical _pid_ argument is
           interpreted in the range of that namespace. As such, the caller's
           idea of the target _pid_ may differ from that of the target process
           when they are operating in different pid namespaces. See
           pid_namespaces(7) for details.  Further, the returned _cap_t_ value
           holds the capabilities that the target _pid_ thinks it has. If the
           target is operating in a (**CLONE_NEWUSER**) namespace, the system
           wide privilege of those user namespace capabilities may be
           substantially reduced. See user_namespaces(7) for details.
    
           **cap_get_bound**() with a _cap_ as an argument returns the current
           value of this bounding set capability flag in effect for the
           calling process. This operation is unprivileged. Note, a macro
           function **CAP_IS_SUPPORTED(cap_value_t** cap**)** is provided that
           evaluates to true (1) if the system supports the specified
           capability, _cap_.  If the system does not support the capability,
           this function returns 0. This macro works by testing for an error
           condition with **cap_get_bound**().
    
           **cap_drop_bound**() can be used to lower the specified bounding set
           capability, **cap**.  To complete successfully, the prevailing
           _effective_ capability set must have a raised **CAP_SETPCAP**.
    
           **cap_get_ambient**() returns the prevailing value of the specified
           ambient capability, or -1 if the capability is not supported by
           the running kernel.  A macro **CAP_AMBIENT_SUPPORTED**() uses this
           function to determine if ambient capabilities are supported by the
           kernel.
    
           **cap_set_ambient**() sets the specified ambient capability to a
           specific value. To raise a specific ambient capability the
           _inheritable_ and _permitted_ flags of the calling process must
           contain the specified capability value. Raised ambient bits will
           only be retained as long as this remains true of the inheritable
           and permitted flags.
    
           **cap_reset_ambient**() resets all of the ambient capabilities for the
           calling process to their lowered value. Note, the ambient set is
           intended to operate in a legacy environment where the application
           has limited awareness of capabilities in general. Executing a
           file, with associated filesystem capabilities, the kernel will
           implicitly reset the ambient set of the process. Further, changes
           to the inheritable set by the program code without explicitly
           fixing up the ambient set can also drop ambient bits.
    
           **cap_get_secbits**() returns the securebits of the calling process.
           These bits affect the way in which the calling process implements
           things like setuid-root fixup and ambient capabilities.
    
           **cap_set_secbits**() attempts to modify the securebits of the calling
           process. Note **CAP_SETPCAP** must be in the effective capability set
           for this to be effective. Some settings lock the sub-states of the
           securebits, so attempts to set values may be denied by the kernel
           even when the **CAP_SETPCAP** capability is raised.
    
           To help manage the complexity of the securebits, libcap provides a
           combined securebit and capability set concept called a libcap
           mode.  **cap_get_mode**() attempts to summarize the prevailing
           security environment in the form of a numerical **cap_mode_t** value.
           A text representation of the mode can be obtained via the
           **cap_mode_name**() function. The vast majority of combinations of
           these values are not well defined in terms of a libcap mode, and
           for these states **cap_get_mode**() returns (**cap_mode_t**)0 which
           **cap_get_name**() identifies as ``_UNCERTAIN_ ''.  Supported modes are:
           **CAP_MODE_NOPRIV** , **CAP_MODE_HYBRID** , **CAP_MODE_PURE1E** and
           **CAP_MODE_PURE1E_INIT**.
    
           **cap_prctl**() can be used to read state via the **prctl** _()_ **system call.**
    
           **cap_prctlw**() can be used to write state via the **prctl** _()_ **system**
           **call.**
    
           **cap_set_mode**() can be used to set the desired mode. The permitted
           capability **CAP_SETPCAP** is required for this function to succeed.
    
           **cap_setuid**() is a convenience function for the setuid(2) system
           call. Where **cap_setuid**() arranges for the right effective
           capability to be raised in order to perform the system call, and
           also arranges to preserve the availability of permitted
           capabilities after the uid has changed. Following this call all
           effective capabilities are lowered.
    
           **cap_setgroups**() is a convenience function for performing both
           setgid(2) and setgroups(2) calls in one call. The **cap_setgroups**()
           call raises the right effective capability for the duration of the
           call, and empties the effective capability set before returning.
    


## RETURN VALUE



           The functions **cap_get_proc**() and **cap_get_pid**() return a non-NULL
           value on success, and NULL on failure.
    
           The function **cap_get_bound**() returns -1 if the requested
           capability is unknown, otherwise the return value reflects the
           current state of that capability in the prevailing bounding set.
           Note, a macro function,
    
           The all of the setting functions such as **cap_set_proc**() and
           **cap_drop_bound**() return zero for success, and -1 on failure.
    
           On failure, _errno_ is set to **EINVAL** , **EPERM** , or **ENOMEM**.
    


## CONFORMING TO



           **cap_set_proc**() and **cap_get_proc**() are specified in the withdrawn
           POSIX.1e draft specification.  **cap_get_pid**() is a Linux extension.
    


## NOTES



           Neither glibc, nor the Linux kernel honors POSIX semantics for
           setting capabilities and securebits in the presence of pthreads.
           That is, changing capability sets, by default, only affect the
           running thread. To be meaningfully secure, however, the capability
           sets should be mirrored by all threads within a common program
           because threads are not memory isolated. As a workaround for this,
           **libcap** is packaged with a separate POSIX semantics system call
           library: **libpsx**.  If your program uses POSIX threads, to achieve
           meaningful POSIX semantics capability manipulation, you should
           link your program with:
    
           **ld ... -lcap $(pkg-config --libs --cflags libpsx)**
    
           or,
    
           **gcc ... -lcap $(pkg-config --libs --cflags libpsx)**
    
           When linked this way, due to linker magic, libcap uses
           psx_syscall(3) and psx_syscall6(3) to perform state setting system
           calls. Notably, this also ensures that **cap_prctlw** _()_ can be used to
           ensure process control bits are shared over all threads of a
           single process.
    
       **capgetp() and capsetp()**
           The library also supports the deprecated functions:
    
           **int capgetp(pid_t** _pid_**, cap_t** _cap_d_**);**
    
           **int capsetp(pid_t** _pid_**, cap_t** _cap_d_**);**
    
           **capgetp**() attempts to obtain the capabilities of some other
           process; storing the capabilities in a pre-allocated _cap_d_.  See
           **cap_init**() for information on allocating an empty capability set.
           This function is deprecated; you should use **cap_get_pid**().
    
           **capsetp**() attempts to set the capabilities of the calling process
           or of some other process(es), _pid_.  Note that setting capabilities
           of another process is only possible on older kernels that do not
           provide VFS support for setting file capabilities.  See capset(2)
           for information on which kernels provide such support.
    
           If _pid_ is positive it refers to a specific process;  if it is
           zero, it refers to the calling process; -1 refers to all processes
           other than the calling process and process '1' (typically
           **init**(8)); other negative values refer to the _-pid_ process group.
    
           In order to use this function, the kernel must support it and the
           calling process must have **CAP_SETPCAP** raised in its Effective
           capability set. The capabilities set in the target process(es) are
           those contained in _cap_d_.
    
           Kernels that support filesystem capabilities redefine the
           semantics of **CAP_SETPCAP** and on such systems, **capsetp**() will
           always fail for any target not equal to the calling process.
           **capsetp**() returns zero for success, and -1 on failure.
    
           On kernels where it is (was) supported, **capsetp**() should be used
           with care.  It existed, primarily, to overcome an early lack of
           support for capabilities in the filesystems supported by Linux.
           Note that on older kernels where **capsetp**() could be used to set
           the capabilities of another process, the only processes that had
           **CAP_SETPCAP** available to them by default were processes started as
           kernel threads.  (Typically this includes **init**(8), kflushd and
           kswapd.) A kernel recompilation was needed to modify this default.
    


## EXAMPLE



           The code segment below raises the **CAP_FOWNER** and **CAP_SETFCAP**
           effective capabilities for the caller:
    
               ...
               cap_t caps;
               const cap_value_t cap_list[2] = {CAP_FOWNER, CAP_SETFCAP};
    
               if (!CAP_IS_SUPPORTED(CAP_SETFCAP))
                   /* handle error */
    
               caps = cap_get_proc();
               if (caps == NULL)
                   /* handle error */;
    
               if (cap_set_flag(caps, CAP_EFFECTIVE, 2, cap_list, CAP_SET) == -1)
                   /* handle error */;
    
               if (cap_set_proc(caps) == -1)
                   /* handle error */;
    
               if (cap_free(caps) == -1)
                   /* handle error */;
               ...
    
           Alternatively, to completely drop privilege in a program launched
           setuid-root but wanting to run as a specific user ID etc. in such
           a way that neither it, nor any of its children can acquire
           privilege again:
    
               ...
               uid_t nobody = 65534;
               const gid_t groups[] = {65534};
    
               if (cap_setgroups(groups[0], 1, groups) != 0)
                   /* handle error */;
               if (cap_setuid(nobody) != 0)
                   /* handle error */;
    
               /*
                * privilege is still available here
                */
    
               if (cap_set_mode(CAP_MODE_NOPRIV) != 0)
                   /* handle error */
               ...
    
           Note, the above sequence can be performed by the **capsh** tool as
           follows:
    
           **sudo capsh --user=nobody --mode=NOPRIV --print**
    
           where **--print** displays the resulting privilege state.
    


* * *