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remove %n support from printf(9)

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It can be dangerous and there is no need for it in the kernel.
Inspired by Kees Cook's change in Linux, and later OpenBSD.

Reviewed by:	cem, gordon, philip
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D24760
This commit is contained in:
Ed Maste 2020-05-09 15:56:02 +00:00
parent 75c600d287
commit 937b352e23
2 changed files with 17 additions and 9 deletions
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8
share/man/man9/printf.9
View File

@ -26,7 +26,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd November 18, 2015
.Dd May 9, 2020
.Dt PRINTF 9
.Os
.Sh NAME
@ -83,7 +83,7 @@ parameter in the same manner as
.Xr printf 3 .
However,
.Xr printf 9
adds two other conversion specifiers.
adds two other conversion specifiers and omits one.
.Pp
The
.Cm \&%b
@ -121,6 +121,10 @@ If present, a width directive will specify the number of bytes to display.
By default, 16 bytes of data are output.
.Pp
The
.Cm \&%n
conversion specifier is not supported.
.Pp
The
.Fn log
function uses
.Xr syslog 3

18
sys/kern/subr_prf.c
View File

@ -775,20 +775,24 @@ reswitch: switch (ch = (u_char)*fmt++) {
lflag = 1;
goto reswitch;
case 'n':
/*
* We do not support %n in kernel, but consume the
* argument.
*/
if (jflag)
*(va_arg(ap, intmax_t *)) = retval;
(void)va_arg(ap, intmax_t *);
else if (qflag)
*(va_arg(ap, quad_t *)) = retval;
(void)va_arg(ap, quad_t *);
else if (lflag)
*(va_arg(ap, long *)) = retval;
(void)va_arg(ap, long *);
else if (zflag)
*(va_arg(ap, size_t *)) = retval;
(void)va_arg(ap, size_t *);
else if (hflag)
*(va_arg(ap, short *)) = retval;
(void)va_arg(ap, short *);
else if (cflag)
*(va_arg(ap, char *)) = retval;
(void)va_arg(ap, char *);
else
*(va_arg(ap, int *)) = retval;
(void)va_arg(ap, int *);
break;
case 'o':
base = 8;