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freebsd-dev/lib/libc/gen/fmtcheck.3

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Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.\" Copyright (c) 2000 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This file was contributed to The NetBSD Foundation by Allen Briggs.
.\"
.\" 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.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the NetBSD
.\" Foundation, Inc. and its contributors.
.\" 4. Neither the name of The NetBSD Foundation nor the names of its
.\" contributors may be used to endorse or promote products derived
.\" from this software without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. 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 FOUNDATION 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.
.\"
.\" $FreeBSD$
Add a Bugs section and note that fmtcheck() is out of sync with printf(); it does not recognise any of the conversions or modifiers added in C99.
2002-10-16 04:03:02 +00:00
.Dd October 16, 2002
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Os
.Dt FMTCHECK 3
.Sh NAME
.Nm fmtcheck
mdoc(7) police: expand plain text xrefs.
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.Nd sanitizes user-supplied
.Xr printf 3 Ns -style
format string
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
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.In stdio.h
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Ft const char *
.Fn fmtcheck "const char *fmt_suspect" "const char *fmt_default"
.Sh DESCRIPTION
The
mdoc(7) police: fix markup.
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.Fn fmtcheck
scans
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Fa fmt_suspect
and
.Fa fmt_default
to determine if
.Fa fmt_suspect
will consume the same argument types as
.Fa fmt_default
and to ensure that
.Fa fmt_suspect
is a valid format string.
.Pp
The
.Xr printf 3
can not -> cannot.
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family of functions cannot verify the types of arguments that they are
Mechanically kill hard sentence breaks.
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passed at run-time.
In some cases, like
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Xr catgets 3 ,
it is useful or necessary to use a user-supplied format string with no
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guarantee that the format string matches the specified arguments.
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Pp
The
mdoc(7) police: fix markup.
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.Fn fmtcheck
was designed to be used in these cases, as in:
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Bd -literal -offset indent
printf(fmtcheck(user_format, standard_format), arg1, arg2);
.Ed
.Pp
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In the check, field widths, fillers, precisions, etc.\& are ignored (unless
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
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the field width or precision is an asterisk
.Ql *
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instead of a digit string).
Also, any text other than the format specifiers
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
is completely ignored.
.Sh RETURN VALUES
If
.Fa fmt_suspect
is a valid format and consumes the same argument types as
.Fa fmt_default ,
then the
mdoc(7) police: fix markup.
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.Fn fmtcheck
will return
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Fa fmt_suspect .
Otherwise, it will return
.Fa fmt_default .
Move appropriate information out of `DESCRIPTION' and into `SECURITY CONSIDERATIONS'. Sponsored by: DARPA, NAI Labs
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.Sh SECURITY CONSIDERATIONS
Note that the formats may be quite different as long as they accept the
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same arguments.
For example,
Move appropriate information out of `DESCRIPTION' and into `SECURITY CONSIDERATIONS'. Sponsored by: DARPA, NAI Labs
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.Qq Li "%p %o %30s %#llx %-10.*e %n"
is compatible with
.Qq Li "This number %lu %d%% and string %s has %qd numbers and %.*g floats (%n)" .
However,
.Qq Li %o
is not equivalent to
.Qq Li %lx
because
the first requires an integer and the second requires a long.
Add fmtcheck(), a function for checking consistency of format string arguments where the format string is obtained from user data, or otherwise difficult to verify statically. Example usage: printf(fmtcheck(user_format, standard_format), arg1, arg2); checks the format string user_format for consistency (same number/order/ type of format operators) with standard_format. If they differ, standard_format is used instead to avoid potential crashes or security violations. Obtained from: NetBSD Reviewed by: -arch
2001-04-17 07:59:52 +00:00
.Sh SEE ALSO
.Xr printf 3
Add a Bugs section and note that fmtcheck() is out of sync with printf(); it does not recognise any of the conversions or modifiers added in C99.
2002-10-16 04:03:02 +00:00
.Sh BUGS
The
.Fn fmtcheck
function does not understand all of the conversions that
.Xr printf 3
does.
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