[PATCH 4.4 62/64] reboot: fix overflow parsing reboot cpu number

Greg Kroah-Hartman
2020-11-17T14:05:29Z

From: Matteo Croce <mcroce@microsoft.com>

commit df5b0ab3e08a156701b537809914b339b0daa526 upstream.

Limit the CPU number to num_possible_cpus(), because setting it to a
value lower than INT_MAX but higher than NR_CPUS produces the following
error on reboot and shutdown:

BUG: unable to handle page fault for address: ffffffff90ab1bb0
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 1c09067 P4D 1c09067 PUD 1c0a063 PMD 0
Oops: 0000 [#1] SMP
CPU: 1 PID: 1 Comm: systemd-shutdow Not tainted 5.9.0-rc8-kvm #110
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-2.fc32 04/01/2014
RIP: 0010:migrate_to_reboot_cpu+0xe/0x60
Code: ea ea 00 48 89 fa 48 c7 c7 30 57 f1 81 e9 fa ef ff ff 66 2e 0f 1f 84 00 00 00 00 00 53 8b 1d d5 ea ea 00 e8 14 33 fe ff 89 da <48> 0f a3 15 ea fc bd 00 48 89 d0 73 29 89 c2 c1 e8 06 65 48 8b 3c
RSP: 0018:ffffc90000013e08 EFLAGS: 00010246
RAX: ffff88801f0a0000 RBX: 0000000077359400 RCX: 0000000000000000
RDX: 0000000077359400 RSI: 0000000000000002 RDI: ffffffff81c199e0
RBP: ffffffff81c1e3c0 R08: ffff88801f41f000 R09: ffffffff81c1e348
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 00007f32bedf8830 R14: 00000000fee1dead R15: 0000000000000000
FS: 00007f32bedf8980(0000) GS:ffff88801f480000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffffffff90ab1bb0 CR3: 000000001d057000 CR4: 00000000000006a0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
__do_sys_reboot.cold+0x34/0x5b
do_syscall_64+0x2d/0x40

Fixes: 1b3a5d02ee07 ("reboot: move arch/x86 reboot= handling to generic kernel")
Signed-off-by: Matteo Croce <mcroce@microsoft.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Fabian Frederick <fabf@skynet.be>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Robin Holt <robinmholt@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lkml.kernel.org/r/20201103214025.116799-3-mcroce@linux.microsoft.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
[sudip: use reboot_mode instead of mode]
Signed-off-by: Sudip Mukherjee <sudipm.mukherjee@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/reboot.c | 7 +++++++
1 file changed, 7 insertions(+)

--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -519,6 +519,13 @@ static int __init reboot_setup(char *str
reboot_cpu = simple_strtoul(str+3, NULL, 0);
else
reboot_mode = REBOOT_SOFT;
+ if (reboot_cpu >= num_possible_cpus()) {
+ pr_err("Ignoring the CPU number in reboot= option. "
+ "CPU %d exceeds possible cpu number %d\n",
+ reboot_cpu, num_possible_cpus());
+ reboot_cpu = 0;
+ break;
+ }
break;