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1 | .\" Hey Emacs! This file is -*- nroff -*- source. |
2 | .\" | |
3 | .\" Copyright (C) 1998 Andries Brouwer (aeb@cwi.nl) | |
73d3ac53 | 4 | .\" and Copyright (C) 2002, 2006, 2008, 2012, 2013 Michael Kerrisk <mtk.manpages@gmail.com> |
af5f9508 | 5 | .\" and Copyright Guillem Jover <guillem@hadrons.org> |
fea681da MK |
6 | .\" |
7 | .\" Permission is granted to make and distribute verbatim copies of this | |
8 | .\" manual provided the copyright notice and this permission notice are | |
9 | .\" preserved on all copies. | |
10 | .\" | |
11 | .\" Permission is granted to copy and distribute modified versions of this | |
12 | .\" manual under the conditions for verbatim copying, provided that the | |
13 | .\" entire resulting derived work is distributed under the terms of a | |
14 | .\" permission notice identical to this one. | |
c13182ef | 15 | .\" |
fea681da MK |
16 | .\" Since the Linux kernel and libraries are constantly changing, this |
17 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
18 | .\" responsibility for errors or omissions, or for damages resulting from | |
19 | .\" the use of the information contained herein. The author(s) may not | |
20 | .\" have taken the same level of care in the production of this manual, | |
21 | .\" which is licensed free of charge, as they might when working | |
22 | .\" professionally. | |
c13182ef | 23 | .\" |
fea681da MK |
24 | .\" Formatted or processed versions of this manual, if unaccompanied by |
25 | .\" the source, must acknowledge the copyright and authors of this work. | |
26 | .\" | |
27 | .\" Modified Thu Nov 11 04:19:42 MET 1999, aeb: added PR_GET_PDEATHSIG | |
28 | .\" Modified 27 Jun 02, Michael Kerrisk | |
c13182ef | 29 | .\" Added PR_SET_DUMPABLE, PR_GET_DUMPABLE, |
fea681da | 30 | .\" PR_SET_KEEPCAPS, PR_GET_KEEPCAPS |
e87fdd92 MK |
31 | .\" Modified 2006-08-30 Guillem Jover <guillem@hadrons.org> |
32 | .\" Updated Linux versions where the options where introduced. | |
33 | .\" Added PR_SET_TIMING, PR_GET_TIMING, PR_SET_NAME, PR_GET_NAME, | |
34 | .\" PR_SET_UNALIGN, PR_GET_UNALIGN, PR_SET_FPEMU, PR_GET_FPEMU, | |
35 | .\" PR_SET_FPEXC, PR_GET_FPEXC | |
8ab8b43f MK |
36 | .\" 2008-04-29 Serge Hallyn, Document PR_CAPBSET_READ and PR_CAPBSET_DROP |
37 | .\" 2008-06-13 Erik Bosman, <ejbosman@cs.vu.nl> | |
38 | .\" Document PR_GET_TSC and PR_SET_TSC. | |
39 | .\" 2008-06-15 mtk, Document PR_SET_SECCOMP, PR_GET_SECCOMP | |
bc02b3ea | 40 | .\" 2009-10-03 Andi Kleen, document PR_MCE_KILL |
06afe673 | 41 | .\" 2012-04 Cyrill Gorcunov, Document PR_SET_MM |
bc02b3ea MK |
42 | .\" 2012-04-25 Michael Kerrisk, Document PR_TASK_PERF_EVENTS_DISABLE and |
43 | .\" PR_TASK_PERF_EVENTS_ENABLE | |
34447828 | 44 | .\" 2012-09-20 Kees Cook, update PR_SET_SECCOMP for mode 2 |
f83fe154 | 45 | .\" 2012-09-20 Kees Cook, document PR_SET_NO_NEW_PRIVS, PR_GET_NO_NEW_PRIVS |
934487a0 MK |
46 | .\" 2012-10-25 Michael Kerrisk, Document PR_SET_TIMERSLACK and |
47 | .\" PR_GET_TIMERSLACK | |
491b2e75 | 48 | .\" 2013-01-10 Kees Cook, document PR_SET_PTRACER |
73d3ac53 | 49 | .\" 2012-02-04 Michael kerrisk, document PR_{SET,GET}_CHILD_SUBREAPER |
fea681da | 50 | .\" |
e14baeeb | 51 | .\" |
73d3ac53 | 52 | .TH PRCTL 2 2013-02-08 "Linux" "Linux Programmer's Manual" |
fea681da MK |
53 | .SH NAME |
54 | prctl \- operations on a process | |
55 | .SH SYNOPSIS | |
521bf584 | 56 | .nf |
fea681da MK |
57 | .B #include <sys/prctl.h> |
58 | .sp | |
521bf584 MK |
59 | .BI "int prctl(int " option ", unsigned long " arg2 ", unsigned long " arg3 , |
60 | .BI " unsigned long " arg4 ", unsigned long " arg5 ); | |
61 | .fi | |
fea681da | 62 | .SH DESCRIPTION |
e511ffb6 | 63 | .BR prctl () |
fea681da | 64 | is called with a first argument describing what to do |
1a329b56 | 65 | (with values defined in \fI<linux/prctl.h>\fP), and further |
c4bb193f | 66 | arguments with a significance depending on the first one. |
fea681da MK |
67 | The first argument can be: |
68 | .TP | |
2e781e20 | 69 | .BR PR_CAPBSET_READ " (since Linux 2.6.25)" |
8ab8b43f MK |
70 | Return (as the function result) 1 if the capability specified in |
71 | .I arg2 | |
72 | is in the calling thread's capability bounding set, | |
73 | or 0 if it is not. | |
74 | (The capability constants are defined in | |
75 | .IR <linux/capability.h> .) | |
76 | The capability bounding set dictates | |
77 | whether the process can receive the capability through a | |
2914a14d | 78 | file's permitted capability set on a subsequent call to |
8ab8b43f MK |
79 | .BR execve (2). |
80 | ||
81 | If the capability specified in | |
82 | .I arg2 | |
83 | is not valid, then the call fails with the error | |
84 | .BR EINVAL . | |
85 | .TP | |
86 | .BR PR_CAPBSET_DROP " (since Linux 2.6.25)" | |
87 | If the calling thread has the | |
88 | .B CAP_SETPCAP | |
89 | capability, then drop the capability specified by | |
90 | .I arg2 | |
91 | from the calling thread's capability bounding set. | |
92 | Any children of the calling thread will inherit the newly | |
93 | reduced bounding set. | |
94 | ||
95 | The call fails with the error: | |
96 | .B EPERM | |
2914a14d | 97 | if the calling thread does not have the |
8ab8b43f MK |
98 | .BR CAP_SETPCAP ; |
99 | .BR EINVAL | |
100 | if | |
101 | .I arg2 | |
102 | does not represent a valid capability; or | |
103 | .BR EINVAL | |
104 | if file capabilities are not enabled in the kernel, | |
105 | in which case bounding sets are not supported. | |
73d3ac53 MK |
106 | |
107 | .TP | |
108 | .BR PR_SET_CHILD_SUBREAPER " (since Linux 3.4)" | |
109 | .\" commit ebec18a6d3aa1e7d84aab16225e87fd25170ec2b | |
110 | If | |
111 | .I arg2 | |
112 | is nonzero, | |
113 | set the "child subreaper" attribute of the calling process; | |
114 | if | |
115 | .I arg2 | |
116 | is zero, unset the attribute. | |
117 | When a process is marked as a child subreaper, | |
118 | all of the children that it creates, and their descendants, | |
119 | will be marked as having a subreaper. | |
120 | In effect, a subreaper fulfills the role of | |
121 | .BR init (1) | |
122 | for its descendant processes. | |
123 | Upon termination of a process | |
124 | that is orphaned (i.e., its immediate parent has already terminated) | |
125 | and marked as having a subreaper, | |
126 | the nearest still living ancestor subreaper | |
127 | will receive a | |
128 | .BR SIGCHLD | |
129 | signal and be able to | |
130 | .BR wait (2) | |
131 | on the process to discover its termination status. | |
132 | ||
133 | .TP | |
134 | .BR PR_GET_CHILD_SUBREAPER " (since Linux 3.4)" | |
135 | Return the "child subreaper" setting of the caller, | |
136 | in the location pointed to by | |
137 | .IR "(int\ *) arg2" . | |
138 | ||
8ab8b43f | 139 | .TP |
88989295 MK |
140 | .BR PR_SET_DUMPABLE " (since Linux 2.3.20)" |
141 | Set the state of the flag determining whether core dumps are produced | |
6f620318 | 142 | for the calling process upon delivery of a signal whose default behavior is |
88989295 | 143 | to produce a core dump. |
6f620318 | 144 | (Normally, this flag is set for a process by default, but it is cleared |
88989295 MK |
145 | when a set-user-ID or set-group-ID program is executed and also by |
146 | various system calls that manipulate process UIDs and GIDs). | |
147 | In kernels up to and including 2.6.12, | |
8ab8b43f | 148 | .I arg2 |
88989295 MK |
149 | must be either 0 (process is not dumpable) or 1 (process is dumpable). |
150 | Between kernels 2.6.13 and 2.6.17, the value 2 was also permitted, | |
151 | which caused any binary which normally would not be dumped | |
152 | to be dumped readable by root only; | |
153 | for security reasons, this feature has been removed. | |
154 | .\" See http://marc.theaimsgroup.com/?l=linux-kernel&m=115270289030630&w=2 | |
155 | .\" Subject: Fix prctl privilege escalation (CVE-2006-2451) | |
156 | .\" From: Marcel Holtmann <marcel () holtmann ! org> | |
157 | .\" Date: 2006-07-12 11:12:00 | |
158 | (See also the description of | |
159 | .I /proc/sys/fs/suid_dumpable | |
160 | in | |
161 | .BR proc (5).) | |
cadcf1b1 | 162 | Processes that are not dumpable can not be attached via |
6fdbc779 | 163 | .BR ptrace (2) |
cadcf1b1 | 164 | .BR PTRACE_ATTACH . |
64536a1b | 165 | .TP |
88989295 MK |
166 | .BR PR_GET_DUMPABLE " (since Linux 2.3.20)" |
167 | Return (as the function result) the current state of the calling | |
168 | process's dumpable flag. | |
169 | .\" Since Linux 2.6.13, the dumpable flag can have the value 2, | |
170 | .\" but in 2.6.13 PR_GET_DUMPABLE simply returns 1 if the dumpable | |
c7094399 | 171 | .\" flags has a nonzero value. This was fixed in 2.6.14. |
64536a1b | 172 | .TP |
8ab8b43f | 173 | .BR PR_SET_ENDIAN " (since Linux 2.6.18, PowerPC only)" |
c13182ef | 174 | Set the endian-ness of the calling process to the value given |
64536a1b | 175 | in \fIarg2\fP, which should be one of the following: |
8ab8b43f | 176 | .\" Respectively 0, 1, 2 |
64536a1b MK |
177 | .BR PR_ENDIAN_BIG , |
178 | .BR PR_ENDIAN_LITTLE , | |
179 | or | |
0daa9e92 | 180 | .B PR_ENDIAN_PPC_LITTLE |
64536a1b | 181 | (PowerPC pseudo little endian). |
e87fdd92 | 182 | .TP |
8ab8b43f MK |
183 | .BR PR_GET_ENDIAN " (since Linux 2.6.18, PowerPC only)" |
184 | Return the endian-ness of the calling process, | |
185 | in the location pointed to by | |
186 | .IR "(int\ *) arg2" . | |
187 | .TP | |
8ab8b43f | 188 | .BR PR_SET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)" |
e87fdd92 MK |
189 | Set floating-point emulation control bits to \fIarg2\fP. |
190 | Pass \fBPR_FPEMU_NOPRINT\fP to silently emulate fp operations accesses, or | |
8bd58774 MK |
191 | \fBPR_FPEMU_SIGFPE\fP to not emulate fp operations and send |
192 | .B SIGFPE | |
193 | instead. | |
e87fdd92 | 194 | .TP |
8ab8b43f MK |
195 | .BR PR_GET_FPEMU " (since Linux 2.4.18, 2.5.9, only on ia64)" |
196 | Return floating-point emulation control bits, | |
197 | in the location pointed to by | |
198 | .IR "(int\ *) arg2" . | |
e87fdd92 | 199 | .TP |
8ab8b43f | 200 | .BR PR_SET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)" |
1c44bd5b MK |
201 | Set floating-point exception mode to \fIarg2\fP. |
202 | Pass \fBPR_FP_EXC_SW_ENABLE\fP to use FPEXC for FP exception enables, | |
c45bd688 MK |
203 | \fBPR_FP_EXC_DIV\fP for floating-point divide by zero, |
204 | \fBPR_FP_EXC_OVF\fP for floating-point overflow, | |
205 | \fBPR_FP_EXC_UND\fP for floating-point underflow, | |
206 | \fBPR_FP_EXC_RES\fP for floating-point inexact result, | |
207 | \fBPR_FP_EXC_INV\fP for floating-point invalid operation, | |
e87fdd92 | 208 | \fBPR_FP_EXC_DISABLED\fP for FP exceptions disabled, |
b28f6e56 | 209 | \fBPR_FP_EXC_NONRECOV\fP for async nonrecoverable exception mode, |
e87fdd92 MK |
210 | \fBPR_FP_EXC_ASYNC\fP for async recoverable exception mode, |
211 | \fBPR_FP_EXC_PRECISE\fP for precise exception mode. | |
212 | .TP | |
8ab8b43f MK |
213 | .BR PR_GET_FPEXC " (since Linux 2.4.21, 2.5.32, only on PowerPC)" |
214 | Return floating-point exception mode, | |
215 | in the location pointed to by | |
216 | .IR "(int\ *) arg2" . | |
217 | .TP | |
88989295 MK |
218 | .BR PR_SET_KEEPCAPS " (since Linux 2.2.18)" |
219 | Set the state of the thread's "keep capabilities" flag, | |
028cb080 MK |
220 | which determines whether the threads's permitted |
221 | capability set is cleared when a change is made to the threads's user IDs | |
88989295 | 222 | such that the threads's real UID, effective UID, and saved set-user-ID |
c7094399 | 223 | all become nonzero when at least one of them previously had the value 0. |
028cb080 MK |
224 | By default, the permitted capability set is cleared when such a change is made; |
225 | setting the "keep capabilities" flag prevents it from being cleared. | |
88989295 | 226 | .I arg2 |
028cb080 MK |
227 | must be either 0 (permitted capabilities are cleared) |
228 | or 1 (permitted capabilities are kept). | |
229 | (A thread's | |
230 | .I effective | |
231 | capability set is always cleared when such a credential change is made, | |
232 | regardless of the setting of the "keep capabilities" flag.) | |
233 | The "keep capabilities" value will be reset to 0 on subsequent calls to | |
88989295 MK |
234 | .BR execve (2). |
235 | .TP | |
236 | .BR PR_GET_KEEPCAPS " (since Linux 2.2.18)" | |
237 | Return (as the function result) the current state of the calling threads's | |
238 | "keep capabilities" flag. | |
239 | .TP | |
240 | .BR PR_SET_NAME " (since Linux 2.6.9)" | |
f49202ae | 241 | Set the process name for the calling thread, |
88989295 MK |
242 | using the value in the location pointed to by |
243 | .IR "(char\ *) arg2" . | |
244 | The name can be up to 16 bytes long, | |
245 | .\" TASK_COMM_LEN in include/linux/sched.h | |
bd74a873 | 246 | and should be null-terminated if it contains fewer bytes. |
88989295 MK |
247 | .TP |
248 | .BR PR_GET_NAME " (since Linux 2.6.11)" | |
f49202ae | 249 | Return the name for the calling thread, |
88989295 MK |
250 | in the buffer pointed to by |
251 | .IR "(char\ *) arg2" . | |
252 | The buffer should allow space for up to 16 bytes; | |
bd74a873 | 253 | the returned string will be null-terminated if it is shorter than that. |
88989295 | 254 | .TP |
f83fe154 | 255 | .BR PR_SET_NO_NEW_PRIVS " (since Linux 3.5)" |
0fcc276f MK |
256 | Set the calling process's |
257 | .I no_new_privs | |
258 | bit to the value in | |
259 | .IR arg2 . | |
260 | With | |
b1df3071 | 261 | .I no_new_privs |
0fcc276f MK |
262 | set to 1, |
263 | .BR execve (2) | |
b1df3071 MK |
264 | promises not to grant privileges to do anything |
265 | that could not have been done without the | |
0fcc276f | 266 | .BR execve (2) |
b1df3071 MK |
267 | call (for example, |
268 | rendering the set-user-ID and set-group-ID permission bits, | |
269 | and file capabilities non-functional). | |
270 | Once set, this bit cannot be unset. | |
271 | The setting of this bit is inherited by children created by | |
272 | .BR fork (2) | |
0fcc276f | 273 | and |
b1df3071 MK |
274 | .BR clone (2), |
275 | and preserved across | |
276 | .BR execve (2). | |
19593937 MK |
277 | |
278 | For more information, see the kernel source file | |
279 | .IR Documentation/prctl/no_new_privs.txt . | |
f83fe154 KC |
280 | .TP |
281 | .BR PR_GET_NO_NEW_PRIVS " (since Linux 3.5)" | |
0fcc276f MK |
282 | Return the value of the |
283 | .I no_new_privs | |
284 | bit for the current process. | |
285 | A value of 0 indicates the regular | |
286 | .BR execve (2) | |
287 | behavior. | |
288 | A value of 1 indicates | |
289 | .BR execve (2) | |
b1df3071 | 290 | will operate in the privilege-restricting mode described above. |
f83fe154 | 291 | .TP |
88989295 MK |
292 | .BR PR_SET_PDEATHSIG " (since Linux 2.1.57)" |
293 | Set the parent process death signal | |
294 | of the calling process to \fIarg2\fP (either a signal value | |
295 | in the range 1..maxsig, or 0 to clear). | |
296 | This is the signal that the calling process will get when its | |
297 | parent dies. | |
298 | This value is cleared for the child of a | |
c7c7235c | 299 | .BR fork (2) |
46b7f60e | 300 | and (since Linux 2.4.36 / 2.6.23) |
f49202ae | 301 | when executing a set-user-ID or set-group-ID binary. |
88989295 MK |
302 | .TP |
303 | .BR PR_GET_PDEATHSIG " (since Linux 2.3.15)" | |
304 | Return the current value of the parent process death signal, | |
305 | in the location pointed to by | |
306 | .IR "(int\ *) arg2" . | |
307 | .TP | |
491b2e75 | 308 | .BR PR_SET_PTRACER " (since Linux 3.4)" |
ff03be9a MK |
309 | .\" commit 2d514487faf188938a4ee4fb3464eeecfbdcf8eb |
310 | .\" commit bf06189e4d14641c0148bea16e9dd24943862215 | |
491b2e75 KC |
311 | This is only meaningful when the Yama LSM is enabled and in mode 1 |
312 | ("restricted ptrace", visible via | |
313 | .IR /proc/sys/kernel/yama/ptrace_scope ). | |
2c7d476b MK |
314 | When a "ptracer process ID" is passed in \fIarg2\fP, |
315 | the caller is declaring that the ptracer process can | |
316 | .BR ptrace (2) | |
317 | the calling process as if it were a direct process ancestor. | |
9f4cec52 MK |
318 | Each |
319 | .B PR_SET_PTRACER | |
320 | operation replaces the previous "ptracer process ID". | |
2c7d476b MK |
321 | Employing |
322 | .B PR_SET_PTRACER | |
323 | with | |
324 | .I arg2 | |
325 | set to 0 clears the caller's "ptracer process ID". | |
326 | If | |
327 | .I arg2 | |
328 | is | |
491b2e75 KC |
329 | .BR PR_SET_PTRACER_ANY, |
330 | the ptrace restrictions introduced by Yama are effectively disabled for the | |
2c7d476b | 331 | calling process. |
491b2e75 KC |
332 | |
333 | For further information, see the kernel source file | |
334 | .IR Documentation/security/Yama.txt . | |
335 | .TP | |
8ab8b43f MK |
336 | .BR PR_SET_SECCOMP " (since Linux 2.6.23)" |
337 | .\" See http://thread.gmane.org/gmane.linux.kernel/542632 | |
338 | .\" [PATCH 0 of 2] seccomp updates | |
339 | .\" andrea@cpushare.com | |
d6ef3d57 MK |
340 | Set the secure computing (seccomp) mode for the calling thread, to limit |
341 | the available system calls. | |
34447828 KC |
342 | The seccomp mode is selected via |
343 | .IR arg2 . | |
344 | (The seccomp constants are defined in | |
345 | .IR <linux/seccomp.h> .) | |
346 | ||
347 | With | |
8ab8b43f | 348 | .IR arg2 |
34447828 KC |
349 | set to |
350 | .BR SECCOMP_MODE_STRICT | |
8ab8b43f MK |
351 | the only system calls that the thread is permitted to make are |
352 | .BR read (2), | |
353 | .BR write (2), | |