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utsname: contribute changes to RNG 

On some small machines with little entropy, a quasi-unique hostname is
sometimes a relevant factor. I've seen, for example, 8 character
alpha-numeric serial numbers. In addition, the time at which the hostname
is set is usually a decent measurement of how long early boot took. So,
call add_device_randomness() on new hostnames, which feeds its arguments
to the RNG in addition to a fresh cycle counter.

Low cost hooks like this never hurt and can only ever help, and since
this costs basically nothing for an operation that is never a fast path,
this is an overall easy win.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
This commit is contained in:
Jason A. Donenfeld 2022-09-27 11:35:16 +02:00
parent dd54fd7dfa
commit 37608ba315
2 changed files with 5 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
kernel/sys.c
View File

@ -25,6 +25,7 @@
#include <linux/times.h>
#include <linux/posix-timers.h>
#include <linux/security.h>
#include <linux/random.h>
#include <linux/suspend.h>
#include <linux/tty.h>
#include <linux/signal.h>
@ -1366,6 +1367,7 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
if (!copy_from_user(tmp, name, len)) {
struct new_utsname *u;
add_device_randomness(tmp, len);
down_write(&uts_sem);
u = utsname();
memcpy(u->nodename, tmp, len);
@ -1419,6 +1421,7 @@ SYSCALL_DEFINE2(setdomainname, char __user *, name, int, len)
if (!copy_from_user(tmp, name, len)) {
struct new_utsname *u;
add_device_randomness(tmp, len);
down_write(&uts_sem);
u = utsname();
memcpy(u->domainname, tmp, len);

2
kernel/utsname_sysctl.c
View File

@ -8,6 +8,7 @@
#include <linux/export.h>
#include <linux/uts.h>
#include <linux/utsname.h>
#include <linux/random.h>
#include <linux/sysctl.h>
#include <linux/wait.h>
#include <linux/rwsem.h>
@ -57,6 +58,7 @@ static int proc_do_uts_string(struct ctl_table *table, int write,
* theoretically be incorrect if there are two parallel writes
* at non-zero offsets to the same sysctl.
*/
add_device_randomness(tmp_data, sizeof(tmp_data));
down_write(&uts_sem);
memcpy(get_uts(table), tmp_data, sizeof(tmp_data));
up_write(&uts_sem);