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capget (2)
  • capget (2) ( Русские man: Системные вызовы )
  • >> capget (2) ( Linux man: Системные вызовы )
  •  

    NAME

    capget, capset - set/get capabilities of thread(s)
     
    

    SYNOPSIS

    #undef _POSIX_SOURCE
    #include <sys/capability.h>

    int capget(cap_user_header_t hdrp, cap_user_data_t datap);

    int capset(cap_user_header_t hdrp, const cap_user_data_t datap);  

    DESCRIPTION

    As of Linux 2.2, the power of the superuser (root) has been partitioned into a set of discrete capabilities. Each thread has a set of effective capabilities identifying which capabilities (if any) it may currently exercise. Each thread also has a set of inheritable capabilities that may be passed through an execve(2) call, and a set of permitted capabilities that it can make effective or inheritable.

    These two functions are the raw kernel interface for getting and setting thread capabilities. Not only are these system calls specific to Linux, but the kernel API is likely to change and use of these functions (in particular the format of the cap_user_*_t types) is subject to change with each kernel revision.

    The portable interfaces are cap_set_proc(3) and cap_get_proc(3); if possible you should use those interfaces in applications. If you wish to use the Linux extensions in applications, you should use the easier-to-use interfaces capsetp(3) and capgetp(3).  

    Current details

    Now that you have been warned, some current kernel details. The structures are defined as follows.

    #define _LINUX_CAPABILITY_VERSION_1  0x19980330
    #define _LINUX_CAPABILITY_U32S_1     1
    
    #define _LINUX_CAPABILITY_VERSION_2  0x20071026
    #define _LINUX_CAPABILITY_U32S_2     2
    
    typedef struct __user_cap_header_struct {
       __u32 version;
       int pid;
    } *cap_user_header_t;
    
    typedef struct __user_cap_data_struct {
       __u32 effective;
       __u32 permitted;
       __u32 inheritable;
    } *cap_user_data_t;
    

    The calls will fail with the error EINVAL, and set the version field of hdrp to the kernel preferred value of _LINUX_CAPABILITY_VERSION_? when an unsupported version value is specified. In this way, one can probe what the current preferred capability revision is. Kernels prior to 2.6.25 prefer 32-bit capabilities with version _LINUX_CAPABILITY_VERSION_1, and kernels 2.6.25+ prefer 64-bit capabilities with version _LINUX_CAPABILITY_VERSION_2. Note, 64-bit capabilities use datap[0] and datap[1], whereas 32-bit capabilities only use datap[0].

    Another change affecting the behavior of these system calls is kernel support for file capabilities (VFS capability support). This support is currently a compile time option (added in kernel 2.6.24).

    For capget() calls, one can probe the capabilities of any process by specifying its process ID with the hdrp->pid field value.  

    With VFS Capability Support

    VFS Capability support creates a file-attribute method for adding capabilities to privileged executables. This privilege model obsoletes kernel support for one process asynchronously setting the capabilities of another. That is, with VFS support, for capset() calls the only permitted values for hdrp->pid are 0 or getpid(2), which are equivalent.  

    Without VFS Capability Support

    When the kernel does not support VFS capabilities, capset() calls can operate on the capabilities of the thread specified by the pid field of hdrp when that is non-zero, or on the capabilities of the calling thread if pid is 0. If pid refers to a single-threaded process, then pid can be specified as a traditional process ID; operating on a thread of a multithreaded process requires a thread ID of the type returned by gettid(2). For capset(), pid can also be: -1, meaning perform the change on all threads except the caller and init(8); or a value less than -1, in which case the change is applied to all members of the process group whose ID is -pid.

    For details on the data, see capabilities(7).  

    RETURN VALUE

    On success, zero is returned. On error, -1 is returned, and errno is set appropriately.  

    ERRORS

    EFAULT
    Bad memory address. hdrp must not be NULL. datap may only be NULL when the user is trying to determine the preferred capability version format supported by the kernel.
    EINVAL
    One of the arguments was invalid.
    EPERM
    An attempt was made to add a capability to the Permitted set, or to set a capability in the Effective or Inheritable sets that is not in the Permitted set.
    EPERM
    The caller attempted to use capset() to modify the capabilities of a thread other than itself, but lacked sufficient privilege. For kernels supporting VFS capabilities, this is never permitted. For kernels lacking VFS support, the CAP_SETPCAP capability is required. (A bug in kernels before 2.6.11 meant that this error could also occur if a thread without this capability tried to change its own capabilities by specifying the pid field as a non-zero value (i.e., the value returned by getpid(2)) instead of 0.)
    ESRCH
    No such thread.
     

    CONFORMING TO

    These system calls are Linux-specific.  

    NOTES

    The portable interface to the capability querying and setting functions is provided by the libcap library and is available here:
    http://www.kernel.org/pub/linux/libs/security/linux-privs  

    SEE ALSO

    clone(2), gettid(2), capabilities(7)  

    COLOPHON

    This page is part of release 3.14 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.


     

    Index

    NAME
    SYNOPSIS
    DESCRIPTION
    Current details
    With VFS Capability Support
    Without VFS Capability Support
    RETURN VALUE
    ERRORS
    CONFORMING TO
    NOTES
    SEE ALSO
    COLOPHON


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