include/linux/highuid.h

   1 #ifndef _LINUX_HIGHUID_H
   2 #define _LINUX_HIGHUID_H
   3
   4 #include <linux/config.h>
   5 #include <linux/types.h>
   6
   7 /*
   8  * general notes:
   9  *
  10  * CONFIG_UID16 is defined if the given architecture needs to
  11  * support backwards compatibility for old system calls.
  12  *
  13  * kernel code should use uid_t and gid_t at all times when dealing with
  14  * kernel-private data.
  15  *
  16  * old_uid_t and old_gid_t should only be different if CONFIG_UID16 is
  17  * defined, else the platform should provide dummy typedefs for them
  18  * such that they are equivalent to __kernel_{u,g}id_t.
  19  *
  20  * uid16_t and gid16_t are used on all architectures. (when dealing
  21  * with structures hard coded to 16 bits, such as in filesystems)
  22  */
  23
  24
  25 /*
  26  * This is the "overflow" UID and GID. They are used to signify uid/gid
  27  * overflow to old programs when they request uid/gid information but are
  28  * using the old 16 bit interfaces.
  29  * When you run a libc5 program, it will think that all highuid files or
  30  * processes are owned by this uid/gid.
  31  * The idea is that it's better to do so than possibly return 0 in lieu of
  32  * 65536, etc.
  33  */
  34
  35 extern int overflowuid;
  36 extern int overflowgid;
  37
  38 #define DEFAULT_OVERFLOWUID     65534
  39 #define DEFAULT_OVERFLOWGID     65534
  40
  41 #ifdef CONFIG_UID16
  42
  43 /* prevent uid mod 65536 effect by returning a default value for high UIDs */
  44 #define high2lowuid(uid) ((uid) > 65535 ? (old_uid_t)overflowuid : (old_uid_t)(uid))
  45 #define high2lowgid(gid) ((gid) > 65535 ? (old_gid_t)overflowgid : (old_gid_t)(gid))
  46 /*
  47  * -1 is different in 16 bits than it is in 32 bits
  48  * these macros are used by chown(), setreuid(), ...,
  49  */
  50 #define low2highuid(uid) ((uid) == (old_uid_t)-1 ? (uid_t)-1 : (uid_t)(uid))
  51 #define low2highgid(gid) ((gid) == (old_gid_t)-1 ? (gid_t)-1 : (gid_t)(gid))
  52
  53 /* Avoid extra ifdefs with these macros */
  54
  55 #define SET_UID16(var, uid)     var = high2lowuid(uid)
  56 #define SET_GID16(var, gid)     var = high2lowgid(gid)
  57 #define NEW_TO_OLD_UID(uid)     high2lowuid(uid)
  58 #define NEW_TO_OLD_GID(gid)     high2lowgid(gid)
  59
  60 /* specific to fs/stat.c */
  61 #define SET_OLDSTAT_UID(stat, uid)      (stat).st_uid = high2lowuid(uid)
  62 #define SET_OLDSTAT_GID(stat, gid)      (stat).st_gid = high2lowgid(gid)
  63 #define SET_STAT_UID(stat, uid)         (stat).st_uid = high2lowuid(uid)
  64 #define SET_STAT_GID(stat, gid)         (stat).st_gid = high2lowgid(gid)
  65
  66 #else
  67
  68 #define SET_UID16(var, uid)     do { ; } while (0)
  69 #define SET_GID16(var, gid)     do { ; } while (0)
  70 #define NEW_TO_OLD_UID(uid)     (uid)
  71 #define NEW_TO_OLD_GID(gid)     (gid)
  72
  73 #define SET_OLDSTAT_UID(stat, uid)      (stat).st_uid = (uid)
  74 #define SET_OLDSTAT_GID(stat, gid)      (stat).st_gid = (gid)
  75 #define SET_STAT_UID(stat, uid)         (stat).st_uid = (uid)
  76 #define SET_STAT_GID(stat, gid)         (stat).st_gid = (gid)
  77
  78 #endif /* CONFIG_UID16 */
  79
  80
  81 /*
  82  * Everything below this line is needed on all architectures, to deal with
  83  * filesystems that only store 16 bits of the UID/GID, etc.
  84  */
  85
  86 /*
  87  * This is the UID and GID that will get written to disk if a filesystem
  88  * only supports 16-bit UIDs and the kernel has a high UID/GID to write
  89  */
  90 extern int fs_overflowuid;
  91 extern int fs_overflowgid;
  92
  93 #define DEFAULT_FS_OVERFLOWUID  65534
  94 #define DEFAULT_FS_OVERFLOWGID  65534
  95
  96 /*
  97  * Since these macros are used in architectures that only need limited
  98  * 16-bit UID back compatibility, we won't use old_uid_t and old_gid_t
  99  */
 100 #define fs_high2lowuid(uid) ((uid) > 65535 ? (uid16_t)fs_overflowuid : (uid16_t)(uid))
 101 #define fs_high2lowgid(gid) ((gid) > 65535 ? (gid16_t)fs_overflowgid : (gid16_t)(gid))
 102
 103 #define low_16_bits(x)  ((x) & 0xFFFF)
 104 #define high_16_bits(x) (((x) & 0xFFFF0000) >> 16)
 105
 106 #endif /* _LINUX_HIGHUID_H */