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ddb(4): Add 'sysctl' command

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Implement `sysctl` in `ddb` by overriding `SYSCTL_OUT`.  When handling the
req, we install custom ddb in/out handlers.  The out handler prints straight
to the debugger, while the in handler ignores all input.  This is intended
to allow us to print just about any sysctl.

There is a known issue when used from ddb(4) entered via 'sysctl
debug.kdb.enter=1'.  The DDB mode does not quite prevent all lock
interactions, and it is possible for the recursive Giant lock to be unlocked
when the ddb(4) 'sysctl' command is used.  This may result in a panic on
return from ddb(4) via 'c' (continue).  Obviously, this is not a problem
when debugging already-paniced systems.

Submitted by:	Travis Lane (formerly: <travis.lane AT isilon.com>)
Reviewed by:	vangyzen (earlier version), Don Morris <dgmorris AT earthlink.net>
Sponsored by:	Dell EMC Isilon
Differential Revision:	https://reviews.freebsd.org/D20219
This commit is contained in:
cem 2019-08-08 00:42:29 +00:00
parent a32748fbf7
commit 63c98f9ad4
1 changed files with 536 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

538
sys/kern/kern_sysctl.c
View File

@ -41,6 +41,7 @@
__FBSDID("$FreeBSD$");
#include "opt_capsicum.h"
#include "opt_ddb.h"
#include "opt_ktrace.h"
#include <sys/param.h>
@ -48,6 +49,7 @@ __FBSDID("$FreeBSD$");
#include <sys/systm.h>
#include <sys/capsicum.h>
#include <sys/kernel.h>
#include <sys/limits.h>
#include <sys/sysctl.h>
#include <sys/malloc.h>
#include <sys/priv.h>
@ -64,6 +66,12 @@ __FBSDID("$FreeBSD$");
#include <sys/ktrace.h>
#endif
#ifdef DDB
#include <sys/kdb.h>
#include <ddb/ddb.h>
#include <ddb/db_lex.h>
#endif
#include <net/vnet.h>
#include <security/mac/mac_framework.h>
@ -1609,9 +1617,10 @@ sysctl_handle_string(SYSCTL_HANDLER_ARGS)
/*
* A zero-length buffer indicates a fixed size read-only
* string:
* string. In ddb, don't worry about trying to make a malloced
* snapshot.
*/
if (arg2 == 0) {
if (arg2 == 0 || kdb_active) {
arg2 = strlen((char *)arg1) + 1;
ro_string = 1;
}
@ -2240,3 +2249,528 @@ sbuf_new_for_sysctl(struct sbuf *s, char *buf, int length,
sbuf_set_drain(s, sbuf_sysctl_drain, req);
return (s);
}
#ifdef DDB
/* The current OID the debugger is working with */
static struct sysctl_oid *g_ddb_oid;
/* The current flags specified by the user */
static int g_ddb_sysctl_flags;
/* Check to see if the last sysctl printed */
static int g_ddb_sysctl_printed;
static const int ctl_sign[CTLTYPE+1] = {
[CTLTYPE_INT] = 1,
[CTLTYPE_LONG] = 1,
[CTLTYPE_S8] = 1,
[CTLTYPE_S16] = 1,
[CTLTYPE_S32] = 1,
[CTLTYPE_S64] = 1,
};
static const int ctl_size[CTLTYPE+1] = {
[CTLTYPE_INT] = sizeof(int),
[CTLTYPE_UINT] = sizeof(u_int),
[CTLTYPE_LONG] = sizeof(long),
[CTLTYPE_ULONG] = sizeof(u_long),
[CTLTYPE_S8] = sizeof(int8_t),
[CTLTYPE_S16] = sizeof(int16_t),
[CTLTYPE_S32] = sizeof(int32_t),
[CTLTYPE_S64] = sizeof(int64_t),
[CTLTYPE_U8] = sizeof(uint8_t),
[CTLTYPE_U16] = sizeof(uint16_t),
[CTLTYPE_U32] = sizeof(uint32_t),
[CTLTYPE_U64] = sizeof(uint64_t),
};
#define DB_SYSCTL_NAME_ONLY 0x001 /* Compare with -N */
#define DB_SYSCTL_VALUE_ONLY 0x002 /* Compare with -n */
#define DB_SYSCTL_OPAQUE 0x004 /* Compare with -o */
#define DB_SYSCTL_HEX 0x008 /* Compare with -x */
#define DB_SYSCTL_SAFE_ONLY 0x100 /* Only simple types */
static const char db_sysctl_modifs[] = {
'N', 'n', 'o', 'x',
};
static const int db_sysctl_modif_values[] = {
DB_SYSCTL_NAME_ONLY, DB_SYSCTL_VALUE_ONLY,
DB_SYSCTL_OPAQUE, DB_SYSCTL_HEX,
};
/* Handlers considered safe to print while recursing */
static int (* const db_safe_handlers[])(SYSCTL_HANDLER_ARGS) = {
sysctl_handle_bool,
sysctl_handle_8,
sysctl_handle_16,
sysctl_handle_32,
sysctl_handle_64,
sysctl_handle_int,
sysctl_handle_long,
sysctl_handle_string,
sysctl_handle_opaque,
};
/*
* Use in place of sysctl_old_kernel to print sysctl values.
*
* Compare to the output handling in show_var from sbin/sysctl/sysctl.c
*/
static int
sysctl_old_ddb(struct sysctl_req *req, const void *ptr, size_t len)
{
const u_char *val, *p;
const char *sep1;
size_t intlen, slen;
uintmax_t umv;
intmax_t mv;
int sign, ctltype, hexlen, xflag, error;
/* Suppress false-positive GCC uninitialized variable warnings */
mv = 0;
umv = 0;
slen = len;
val = p = ptr;
if (ptr == NULL) {
error = 0;
goto out;
}
/* We are going to print */
g_ddb_sysctl_printed = 1;
xflag = g_ddb_sysctl_flags & DB_SYSCTL_HEX;
ctltype = (g_ddb_oid->oid_kind & CTLTYPE);
sign = ctl_sign[ctltype];
intlen = ctl_size[ctltype];
switch (ctltype) {
case CTLTYPE_NODE:
case CTLTYPE_STRING:
db_printf("%.*s", (int) len, (const char *) p);
error = 0;
goto out;
case CTLTYPE_INT:
case CTLTYPE_UINT:
case CTLTYPE_LONG:
case CTLTYPE_ULONG:
case CTLTYPE_S8:
case CTLTYPE_S16:
case CTLTYPE_S32:
case CTLTYPE_S64:
case CTLTYPE_U8:
case CTLTYPE_U16:
case CTLTYPE_U32:
case CTLTYPE_U64:
hexlen = 2 + (intlen * CHAR_BIT + 3) / 4;
sep1 = "";
while (len >= intlen) {
switch (ctltype) {
case CTLTYPE_INT:
case CTLTYPE_UINT:
umv = *(const u_int *)p;
mv = *(const int *)p;
break;
case CTLTYPE_LONG:
case CTLTYPE_ULONG:
umv = *(const u_long *)p;
mv = *(const long *)p;
break;
case CTLTYPE_S8:
case CTLTYPE_U8:
umv = *(const uint8_t *)p;
mv = *(const int8_t *)p;
break;
case CTLTYPE_S16:
case CTLTYPE_U16:
umv = *(const uint16_t *)p;
mv = *(const int16_t *)p;
break;
case CTLTYPE_S32:
case CTLTYPE_U32:
umv = *(const uint32_t *)p;
mv = *(const int32_t *)p;
break;
case CTLTYPE_S64:
case CTLTYPE_U64:
umv = *(const uint64_t *)p;
mv = *(const int64_t *)p;
break;
}
db_printf("%s", sep1);
if (xflag)
db_printf("%#0*jx", hexlen, umv);
else if (!sign)
db_printf("%ju", umv);
else if (g_ddb_oid->oid_fmt[1] == 'K') {
/* Kelvins are currently unsupported. */
error = EOPNOTSUPP;
goto out;
} else
db_printf("%jd", mv);
sep1 = " ";
len -= intlen;
p += intlen;
}
error = 0;
goto out;
case CTLTYPE_OPAQUE:
/* TODO: Support struct functions. */
/* FALLTHROUGH */
default:
db_printf("Format:%s Length:%zu Dump:0x",
g_ddb_oid->oid_fmt, len);
while (len-- && (xflag || p < val + 16))
db_printf("%02x", *p++);
if (!xflag && len > 16)
db_printf("...");
error = 0;
goto out;
}
out:
req->oldidx += slen;
return (error);
}
/*
* Avoid setting new sysctl values from the debugger
*/
static int
sysctl_new_ddb(struct sysctl_req *req, void *p, size_t l)
{
if (!req->newptr)
return (0);
/* Changing sysctls from the debugger is currently unsupported */
return (EPERM);
}
/*
* Run a sysctl handler with the DDB oldfunc and newfunc attached.
* Instead of copying any output to a buffer we'll dump it right to
* the console.
*/
static int
db_sysctl(struct sysctl_oid *oidp, int *name, u_int namelen,
void *old, size_t *oldlenp, size_t *retval, int flags)
{
struct sysctl_req req;
int error;
/* Setup the request */
bzero(&req, sizeof req);
req.td = kdb_thread;
req.oldfunc = sysctl_old_ddb;
req.newfunc = sysctl_new_ddb;
req.lock = REQ_UNWIRED;
if (oldlenp) {
req.oldlen = *oldlenp;
}
req.validlen = req.oldlen;
if (old) {
req.oldptr = old;
}
/* Setup our globals for sysctl_old_ddb */
g_ddb_oid = oidp;
g_ddb_sysctl_flags = flags;
g_ddb_sysctl_printed = 0;
error = sysctl_root(0, name, namelen, &req);
/* Reset globals */
g_ddb_oid = NULL;
g_ddb_sysctl_flags = 0;
if (retval) {
if (req.oldptr && req.oldidx > req.validlen)
*retval = req.validlen;
else
*retval = req.oldidx;
}
return (error);
}
/*
* Show a sysctl's name
*/
static void
db_show_oid_name(int *oid, size_t nlen)
{
struct sysctl_oid *oidp;
int qoid[CTL_MAXNAME+2];
int error;
qoid[0] = 0;
memcpy(qoid + 2, oid, nlen * sizeof(int));
qoid[1] = 1;
error = sysctl_find_oid(qoid, nlen + 2, &oidp, NULL, NULL);
if (error)
db_error("sysctl name oid");
error = db_sysctl(oidp, qoid, nlen + 2, NULL, NULL, NULL, 0);
if (error)
db_error("sysctl name");
}
/*
* Check to see if an OID is safe to print from ddb.
*/
static bool
db_oid_safe(const struct sysctl_oid *oidp)
{
for (unsigned int i = 0; i < nitems(db_safe_handlers); ++i) {
if (oidp->oid_handler == db_safe_handlers[i])
return (true);
}
return (false);
}
/*
* Show a sysctl at a specific OID
* Compare to the input handling in show_var from sbin/sysctl/sysctl.c
*/
static int
db_show_oid(struct sysctl_oid *oidp, int *oid, size_t nlen, int flags)
{
int error, xflag, oflag, Nflag, nflag;
size_t len;
xflag = flags & DB_SYSCTL_HEX;
oflag = flags & DB_SYSCTL_OPAQUE;
nflag = flags & DB_SYSCTL_VALUE_ONLY;
Nflag = flags & DB_SYSCTL_NAME_ONLY;
if ((oidp->oid_kind & CTLTYPE) == CTLTYPE_OPAQUE &&
(!xflag && !oflag))
return (0);
if (Nflag) {
db_show_oid_name(oid, nlen);
error = 0;
goto out;
}
if (!nflag) {
db_show_oid_name(oid, nlen);
db_printf(": ");
}
if ((flags & DB_SYSCTL_SAFE_ONLY) && !db_oid_safe(oidp)) {
db_printf("Skipping, unsafe to print while recursing.");
error = 0;
goto out;
}
/* Try once, and ask about the size */
len = 0;
error = db_sysctl(oidp, oid, nlen,
NULL, NULL, &len, flags);
if (error)
goto out;
if (!g_ddb_sysctl_printed)
/* Lie about the size */
error = db_sysctl(oidp, oid, nlen,
(void *) 1, &len, NULL, flags);
out:
db_printf("\n");
return (error);
}
/*
* Show all sysctls under a specific OID
* Compare to sysctl_all from sbin/sysctl/sysctl.c
*/
static int
db_show_sysctl_all(int *oid, size_t len, int flags)
{
struct sysctl_oid *oidp;
int name1[CTL_MAXNAME + 2], name2[CTL_MAXNAME + 2];
size_t l1, l2;
name1[0] = 0;
name1[1] = 2;
l1 = 2;
if (len) {
memcpy(name1+2, oid, len * sizeof(int));
l1 +=len;
} else {
name1[2] = 1;
l1++;
}
for (;;) {
int i, error;
l2 = sizeof(name2);
error = kernel_sysctl(kdb_thread, name1, l1,
name2, &l2, NULL, 0, &l2, 0);
if (error != 0) {
if (error == ENOENT)
return (0);
else
db_error("sysctl(getnext)");
}
l2 /= sizeof(int);
if (l2 < (unsigned int)len)
return (0);
for (i = 0; i < len; i++)
if (name2[i] != oid[i])
return (0);
/* Find the OID in question */
error = sysctl_find_oid(name2, l2, &oidp, NULL, NULL);
if (error)
return (error);
i = db_show_oid(oidp, name2, l2, flags | DB_SYSCTL_SAFE_ONLY);
if (db_pager_quit)
return (0);
memcpy(name1+2, name2, l2 * sizeof(int));
l1 = 2 + l2;
}
}
/*
* Show a sysctl by its user facing string
*/
static int
db_sysctlbyname(char *name, int flags)
{
struct sysctl_oid *oidp;
int oid[CTL_MAXNAME];
int error, nlen;
error = name2oid(name, oid, &nlen, &oidp);
if (error) {
return (error);
}
if ((oidp->oid_kind & CTLTYPE) == CTLTYPE_NODE) {
db_show_sysctl_all(oid, nlen, flags);
} else {
error = db_show_oid(oidp, oid, nlen, flags);
}
return (error);
}
static void
db_sysctl_cmd_usage(void)
{
db_printf(
" sysctl [/Nnox] <sysctl> \n"
" \n"
" <sysctl> The name of the sysctl to show. \n"
" \n"
" Show a sysctl by hooking into SYSCTL_IN and SYSCTL_OUT. \n"
" This will work for most sysctls, but should not be used \n"
" with sysctls that are known to malloc. \n"
" \n"
" While recursing any \"unsafe\" sysctls will be skipped. \n"
" Call sysctl directly on the sysctl to try printing the \n"
" skipped sysctl. This is unsafe and may make the ddb \n"
" session unusable. \n"
" \n"
" Arguments: \n"
" /N Display only the name of the sysctl. \n"
" /n Display only the value of the sysctl. \n"
" /o Display opaque values. \n"
" /x Display the sysctl in hex. \n"
" \n"
"For example: \n"
"sysctl vm.v_free_min \n"
"vn.v_free_min: 12669 \n"
);
}
/*
* Show a specific sysctl similar to sysctl (8).
*/
DB_FUNC(sysctl, db_sysctl_cmd, db_cmd_table, CS_OWN, NULL)
{
char name[TOK_STRING_SIZE];
int error, i, t, flags;
/* Parse the modifiers */
t = db_read_token();
if (t == tSLASH || t == tMINUS) {
t = db_read_token();
if (t != tIDENT) {
db_printf("Bad modifier\n");
error = EINVAL;
goto out;
}
db_strcpy(modif, db_tok_string);
}
else {
db_unread_token(t);
modif[0] = '\0';
}
flags = 0;
for (i = 0; i < nitems(db_sysctl_modifs); i++) {
if (strchr(modif, db_sysctl_modifs[i])) {
flags |= db_sysctl_modif_values[i];
}
}
/* Parse the sysctl names */
t = db_read_token();
if (t != tIDENT) {
db_printf("Need sysctl name\n");
error = EINVAL;
goto out;
}
/* Copy the name into a temporary buffer */
db_strcpy(name, db_tok_string);
/* Ensure there is no trailing cruft */
t = db_read_token();
if (t != tEOL) {
db_printf("Unexpected sysctl argument\n");
error = EINVAL;
goto out;
}
error = db_sysctlbyname(name, flags);
if (error == ENOENT) {
db_printf("unknown oid: '%s'\n", db_tok_string);
goto out;
} else if (error) {
db_printf("%s: error: %d\n", db_tok_string, error);
goto out;
}
out:
/* Ensure we eat all of our text */
db_flush_lex();
if (error == EINVAL) {
db_sysctl_cmd_usage();
}
}
#endif /* DDB */