| ucred.9 (99576) | ucred.9 (100570) |
|---|---|
| 1.\" 2.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as --- 10 unchanged lines hidden (view full) --- 19.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25.\" DAMAGE. 26.\" | 1.\" 2.\" Copyright (C) 2001 Chad David <davidc@acns.ab.ca>. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice(s), this list of conditions and the following disclaimer as --- 10 unchanged lines hidden (view full) --- 19.\" DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES 20.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR 21.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 22.\" CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 23.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 24.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH 25.\" DAMAGE. 26.\" |
| 27.\" $FreeBSD: head/share/man/man9/ucred.9 99576 2002-07-08 07:34:46Z julian $ | 27.\" $FreeBSD: head/share/man/man9/ucred.9 100570 2002-07-23 13:09:24Z rwatson $ |
| 28.\" 29.Dd March 3, 2002 30.Dt UCRED 9 31.Os 32.Sh NAME 33.Nm ucred , 34.Nm crget , 35.Nm crhold , --- 103 unchanged lines hidden (view full) --- 139all return a pointer to a 140.Vt ucred 141structure. 142.Pp 143.Fn crshared 144returns 0 if the credential has a reference count greater than 1; 145otherwise, 1 is returned. 146.Sh USAGE NOTES | 28.\" 29.Dd March 3, 2002 30.Dt UCRED 9 31.Os 32.Sh NAME 33.Nm ucred , 34.Nm crget , 35.Nm crhold , --- 103 unchanged lines hidden (view full) --- 139all return a pointer to a 140.Vt ucred 141structure. 142.Pp 143.Fn crshared 144returns 0 if the credential has a reference count greater than 1; 145otherwise, 1 is returned. 146.Sh USAGE NOTES |
| 147In general in a system call, 148you should always use the | 147As of 148.Fx 5.0 , 149the |
| 149.Vt ucred | 150.Vt ucred |
| 150associated with the 151thread doing the work rather than that of the process attached to it, 152As that associated with the thread is guaranteed to be safely accessed 153under SMP, and will remain stable for the duration of the call, even 154in the face of a multithreaded application changing the process credentials 155from another thread. | 151structure contains extensible fields. 152This means that the correct protocol must always be followed to create 153a fresh and writable credential structure: new credentials must always 154be derived from existing credentials using 155.Fn crget 156and 157.Fn crcopy . 158.Pp 159In the common case, credentials required for access control decisions are 160used in a read-only manner. 161In these circumstances, the thread credential 162.Va td_ucred 163should be used, as it requires no locking to access safely, and remains stable 164for the duration of the call even in the face of a multi-threaded 165application changing the process credentials from another thread. 166Primitives such as 167.Xr suser 9 168will assume the use of 169.Va td_ucred 170unless explicitly specified using 171.Xr suser_cred 9 . 172.Pp 173During a process credential update, the process lock must be held across 174check and update, to prevent race conditions. 175The process credential, 176.Va td->td_proc->p_ucred , 177must be used both for check and update. 178If a process credential is updated during a system call and checks against 179the thread credential are to be made later during the same system call, 180the thread credential must also be refreshed from the process credential 181so as to prevent use of a stale value. 182To avoid this scenario, it is recommended that system calls updating the 183process credential by designed to avoid other authorization functions. 184.Pp 185If temporarily elevated privileges are required for a thread, the thread 186credential can by replaced for the duration of an activity, or for 187the remainder of the system call. 188However, as a thread credential is often shared, appropriate care should be 189taken to make sure modifications are made to a writable credential 190through the use of 191.Fn crget 192and 193.Fn crcopy . 194.Pp 195Caution should be exercised when checking authorization for a thread or 196process perform an operation on another thread or process. 197As a result of temporary elevation, the target thread credential should 198.Em never 199be used as the target credential in an access control decision: the process 200credential associated with the thread, 201.Va td->td_proc->p_ucred , 202should be used instead. 203For example, 204.Xr p_candebug 9 205accepts a target process, not a target thread, for access control purposes. |
| 156.Sh SEE ALSO 157.Xr uihold 9 158.Sh AUTHORS 159This man page was written by 160.An Chad David Aq davidc@acns.ab.ca . | 206.Sh SEE ALSO 207.Xr uihold 9 208.Sh AUTHORS 209This man page was written by 210.An Chad David Aq davidc@acns.ab.ca . |