1CAP_GET_FILE(3) Linux Programmer's Manual CAP_GET_FILE(3)
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6 cap_get_file, cap_set_file, cap_get_fd, cap_set_fd - capability manipu‐
7 lation on files
8
10 #include <sys/capability.h>
11 cap_t cap_get_file(const char *path_p);
13 int cap_set_file(const char *path_p, cap_t cap_p);
15 cap_t cap_get_fd(int fd);
17 int cap_set_fd(int fd, cap_t caps);
19 uid_t cap_get_nsowner(cap_t caps);
21 int cap_set_nsowner(cap_t caps, uid_t rootuid);
23 Link with -lcap.
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27 cap_get_file() and cap_get_fd() allocate a capability state in working
28 storage and set it to represent the capability state of the pathname
29 pointed to by path_p or the file open on descriptor fd. These func‐
30 tions return a pointer to the newly created capability state. The
31 effects of reading the capability state from any file other than a reg‐
32 ular file is undefined. The caller should free any releasable memory,
33 when the capability state in working storage is no longer required, by
34 calling cap_free() with the used cap_t as an argument.
35 cap_set_file() and cap_set_fd() set the values for all capability flags
37 for all capabilities for the pathname pointed to by path_p or the file
38 open on descriptor fd, with the capability state identified by cap_p.
39 The new capability state of the file is completely determined by the
40 contents of cap_p. A NULL value for cap_p is used to indicate that
41 capabilities for the file should be deleted. For these functions to
42 succeed, the calling process must have the CAP_SETFCAP capability in
43 its effective set and either the effective user ID of the process must
44 match the file owner or the calling process must have the CAP_FOWNER
45 capability in its effective capability set. The effects of writing the
46 capability state to any file type other than a regular file are unde‐
47 fined.
48 A capability set held in memory can be associated with the root user ID
50 in use in a specific user namespace. It is possible to get and set this
51 value (in the memory copy) with cap_get_nsowner() and cap_set_nsowner()
52 respectively. The root user ID is ignored by the libcap library in all
53 cases other than when the capability is written to a file. Only if the
54 value is non-zero will the library attempt to include it in the written
55 file capability set.
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58 cap_get_file() and cap_get_fd() return a non-NULL value on success, and
59 NULL on failure.
60 cap_set_file() and cap_set_fd() return zero on success, and -1 on fail‐
62 ure.
63 On failure, errno is set to EACCES, EBADFD, ENAMETOOLONG, ENOENT,
65 ENOMEM, ENOTDIR, EPERM, or EROFS.
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68 These functions are specified by withdrawn POSIX.1e draft specifica‐
69 tion.
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72 Support for file capabilities is provided on Linux since version
73 2.6.24.
74 On Linux, the file Effective set is a single bit. If it is enabled,
76 then all Permitted capabilities are enabled in the Effective set of the
77 calling process when the file is executed; otherwise, no capabilities
78 are enabled in the process's Effective set following an execve(2).
79 Because the file Effective set is a single bit, if any capability is
80 enabled in the Effective set of the cap_t given to cap_set_file() or
81 cap_set_fd(), then all capabilities whose Permitted or Inheritable flag
82 is enabled must also have the Effective flag enabled. Conversely, if
83 the Effective bit is enabled on a file, then the cap_t returned by
84 cap_get_file() and cap_get_fd() will have the Effective flag enabled
85 for each capability that has the Permitted or Inheritable flag enabled.
86
88 libcap(3), cap_clear(3), cap_copy_ext(3), cap_from_text(3),
89 cap_get_proc(3), cap_init(3), capabilities(7), user_namespaces(7)
90 2008-05-11 CAP_GET_FILE(3)