.\" Copyright (c) 2006 Pawel Jakub Dawidek <pjd@FreeBSD.org>
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" $FreeBSD$
.\"
.Dd January 9, 2009
.Dt REDZONE 9
.Os
.Sh NAME
.Nm RedZone
.Nd "buffer corruptions detector"
.Sh SYNOPSIS
.Cd "options KDB"
.Cd "options DDB"
.Cd "options DEBUG_REDZONE"
.Sh DESCRIPTION
.Nm
detects buffer underflow and buffer overflow bugs at runtime.
Currently
.Nm
only detects buffer corruptions for memory allocated with
.Xr malloc 9 .
When such corruption is detected two backtraces are printed on the console.
The first one shows from where memory was allocated, the second one shows from
where memory was freed.
By default the system will not panic when buffer corruption is detected.
This can be changed by setting the
.Va vm.redzone.panic
.Xr sysctl 8
variable to 1.
The amount of extra memory allocated for
.Nm Ns 's
needs is stored in the
.Va vm.redzone.extra_mem
.Xr sysctl 8
variable.
.Sh EXAMPLE
The example below shows the logs from the detection of a buffer underflow and a
buffer overflow.
.Bd -literal -offset indent
REDZONE: Buffer underflow detected. 2 bytes corrupted before 0xc8688580 (16 bytes allocated).
Allocation backtrace:
#0 0xc0583e4e at redzone_setup+0x3c
#1 0xc04a23fa at malloc+0x19e
#2 0xcdeb69ca at redzone_modevent+0x60
#3 0xc04a3f3c at module_register_init+0x82
#4 0xc049d96a at linker_file_sysinit+0x8e
#5 0xc049dc7c at linker_load_file+0xed
#6 0xc04a041f at linker_load_module+0xc4
#7 0xc049e883 at kldload+0x116
#8 0xc05d9b3d at syscall+0x325
#9 0xc05c944f at Xint0x80_syscall+0x1f
Free backtrace:
#0 0xc0583f92 at redzone_check+0xd4
#1 0xc04a2422 at free+0x1c
#2 0xcdeb69a6 at redzone_modevent+0x3c
#3 0xc04a438d at module_unload+0x61
#4 0xc049e0b3 at linker_file_unload+0x89
#5 0xc049e979 at kern_kldunload+0x96
#6 0xc049ea00 at kldunloadf+0x2c
#7 0xc05d9b3d at syscall+0x325
#8 0xc05c944f at Xint0x80_syscall+0x1f

REDZONE: Buffer overflow detected. 4 bytes corrupted after 0xc8688590 (16 bytes allocated).
Allocation backtrace:
#0 0xc0583e4e at redzone_setup+0x3c
#1 0xc04a23fa at malloc+0x19e
#2 0xcdeb69ca at redzone_modevent+0x60
#3 0xc04a3f3c at module_register_init+0x82
#4 0xc049d96a at linker_file_sysinit+0x8e
#5 0xc049dc7c at linker_load_file+0xed
#6 0xc04a041f at linker_load_module+0xc4
#7 0xc049e883 at kldload+0x116
#8 0xc05d9b3d at syscall+0x325
#9 0xc05c944f at Xint0x80_syscall+0x1f
Free backtrace:
#0 0xc0584020 at redzone_check+0x162
#1 0xc04a2422 at free+0x1c
#2 0xcdeb69a6 at redzone_modevent+0x3c
#3 0xc04a438d at module_unload+0x61
#4 0xc049e0b3 at linker_file_unload+0x89
#5 0xc049e979 at kern_kldunload+0x96
#6 0xc049ea00 at kldunloadf+0x2c
#7 0xc05d9b3d at syscall+0x325
#8 0xc05c944f at Xint0x80_syscall+0x1f
.Ed
.Sh SEE ALSO
.Xr sysctl 8 ,
.Xr malloc 9 ,
.Xr memguard 9
.Sh HISTORY
.Nm
first appeared in
.Fx 7.0 .
.Sh AUTHORS
.An Pawel Jakub Dawidek Aq pjd@FreeBSD.org
.Sh BUGS
Currently,
.Nm
does not cooperate with
.Xr memguard 9 .
Allocations from a memory type controlled by
.Xr memguard 9
are simply skipped, so buffer corruptions will not be detected there.