14bdbaf2e4
Coredump notes depend on being able to invoke dump routines twice; once in a dry-run mode to get the size of the note, and another to actually emit the note to the corefile. When a note helper emits a different length section the second time around than the length it requested the first time, the kernel produces a corrupt coredump. NT_PROCSTAT_FILES output length, when packing kinfo structs, is tied to the length of filenames corresponding to vnodes in the process' fd table via vn_fullpath. As vnodes may move around during dump, this is racy. So: - Detect badly behaved notes in putnote() and pad underfilled notes. - Add a fail point, debug.fail_point.fill_kinfo_vnode__random_path to exercise the NT_PROCSTAT_FILES corruption. It simply picks random lengths to expand or truncate paths to in fo_fill_kinfo_vnode(). - Add a sysctl, kern.coredump_pack_fileinfo, to allow users to disable kinfo packing for PROCSTAT_FILES notes. This should avoid both FILES note corruption and truncation, even if filenames change, at the cost of about 1 kiB in padding bloat per open fd. Document the new sysctl in core.5. - Fix note_procstat_files to self-limit in the 2nd pass. Since sometimes this will result in a short write, pad up to our advertised size. This addresses note corruption, at the risk of sometimes truncating the last several fd info entries. - Fix NT_PROCSTAT_FILES consumers libutil and libprocstat to grok the zero padding. With suggestions from: bjk, jhb, kib, wblock Approved by: markj (mentor) Relnotes: yes Sponsored by: EMC / Isilon Storage Division Differential Revision: https://reviews.freebsd.org/D3548
152 lines
4.9 KiB
Groff
152 lines
4.9 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)core.5 8.3 (Berkeley) 12/11/93
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.\" $FreeBSD$
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.\"
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.Dd September 2, 2015
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.Dt CORE 5
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.Os
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.Sh NAME
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.Nm core
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.Nd memory image file format
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.Sh SYNOPSIS
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.In sys/param.h
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.Sh DESCRIPTION
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A small number of signals which cause abnormal termination of a process
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also cause a record of the process's in-core state to be written
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to disk for later examination by one of the available debuggers.
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(See
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.Xr sigaction 2 . )
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This memory image is written to a file named by default
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.Nm programname.core
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in the working directory;
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provided the terminated process had write permission in the directory,
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and provided the abnormality did not cause
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a system crash.
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(In this event, the decision to save the core file is arbitrary, see
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.Xr savecore 8 . )
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.Pp
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The maximum size of a core file is limited by
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.Xr setrlimit 2 .
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Files which would be larger than the limit are not created.
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.Pp
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The name of the file is controlled via the
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.Xr sysctl 8
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variable
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.Va kern.corefile .
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The contents of this variable describes a filename to store
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the core image to.
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This filename can be absolute, or relative (which
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will resolve to the current working directory of the program
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generating it).
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.Pp
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The following format specifiers may be used in the
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.Va kern.corefile
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sysctl to insert additional information into the resulting core file
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name:
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.Bl -tag -width "1234567890" -compact -offset "12345"
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.It Em \&%H
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Machine hostname.
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.It Em \&%I
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An index starting at zero until the sysctl
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.Em debug.ncores
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is reached.
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This can be useful for limiting the number of corefiles
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generated by a particular process.
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.It Em \&%N
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process name.
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.It Em \&%P
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processes PID.
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.It Em \&%U
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process UID.
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.El
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.Pp
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The name defaults to
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.Em \&%N.core ,
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yielding the traditional
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.Fx
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behaviour.
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.Pp
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By default, a process that changes user or group credentials whether
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real or effective will not create a corefile.
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This behaviour can be
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changed to generate a core dump by setting the
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.Xr sysctl 8
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variable
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.Va kern.sugid_coredump
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to 1.
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.Pp
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Corefiles can be compressed by the kernel if the following item
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is included in the kernel configuration file:
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.Bl -tag -width "1234567890" -compact -offset "12345"
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.It options
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GZIO
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.El
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.Pp
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When the GZIO option is included, the following sysctls control whether core
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files will be compressed:
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.Bl -tag -width "kern.compress_user_cores_gzlevel" -compact -offset "12345"
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.It Em kern.compress_user_cores_gzlevel
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Gzip compression level.
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Defaults to 6.
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.It Em kern.compress_user_cores
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Actually compress user cores.
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Compressed core files will have a suffix of
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.Ql .gz
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appended to them.
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.El
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.Sh NOTES
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Corefiles are written with open file descriptor information as an ELF note.
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By default, file paths are packed to only use as much space as needed.
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However, file paths can change at any time, including during core dump,
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and this can result in truncated file descriptor data.
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.Pp
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All file descriptor information can be preserved by disabling packing.
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This potentially wastes up to PATH_MAX bytes per open fd.
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Packing is disabled with
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.Dl sysctl kern.coredump_pack_fileinfo=0 .
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.Sh EXAMPLES
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In order to store all core images in per-user private areas under
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.Pa /var/coredumps ,
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the following
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.Xr sysctl 8
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command can be used:
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.Pp
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.Dl sysctl kern.corefile=/var/coredumps/\&%U/\&%N.core
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.Sh SEE ALSO
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.Xr gdb 1 ,
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.Xr kgdb 1 ,
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.Xr setrlimit 2 ,
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.Xr sigaction 2 ,
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.Xr sysctl 8
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.Sh HISTORY
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A
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.Nm
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file format appeared in
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.At v6 .
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