From 9002b21465fa4d829edfc94a5a441005cffaa972 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Fri, 5 Apr 2019 18:39:38 -0700 Subject: [PATCH] kernel/sysctl.c: fix out-of-bounds access when setting file-max Commit 32a5ad9c2285 ("sysctl: handle overflow for file-max") hooked up min/max values for the file-max sysctl parameter via the .extra1 and .extra2 fields in the corresponding struct ctl_table entry. Unfortunately, the minimum value points at the global 'zero' variable, which is an int. This results in a KASAN splat when accessed as a long by proc_doulongvec_minmax on 64-bit architectures: | BUG: KASAN: global-out-of-bounds in __do_proc_doulongvec_minmax+0x5d8/0x6a0 | Read of size 8 at addr ffff2000133d1c20 by task systemd/1 | | CPU: 0 PID: 1 Comm: systemd Not tainted 5.1.0-rc3-00012-g40b114779944 #2 | Hardware name: linux,dummy-virt (DT) | Call trace: | dump_backtrace+0x0/0x228 | show_stack+0x14/0x20 | dump_stack+0xe8/0x124 | print_address_description+0x60/0x258 | kasan_report+0x140/0x1a0 | __asan_report_load8_noabort+0x18/0x20 | __do_proc_doulongvec_minmax+0x5d8/0x6a0 | proc_doulongvec_minmax+0x4c/0x78 | proc_sys_call_handler.isra.19+0x144/0x1d8 | proc_sys_write+0x34/0x58 | __vfs_write+0x54/0xe8 | vfs_write+0x124/0x3c0 | ksys_write+0xbc/0x168 | __arm64_sys_write+0x68/0x98 | el0_svc_common+0x100/0x258 | el0_svc_handler+0x48/0xc0 | el0_svc+0x8/0xc | | The buggy address belongs to the variable: | zero+0x0/0x40 | | Memory state around the buggy address: | ffff2000133d1b00: 00 00 00 00 00 00 00 00 fa fa fa fa 04 fa fa fa | ffff2000133d1b80: fa fa fa fa 04 fa fa fa fa fa fa fa 04 fa fa fa | >ffff2000133d1c00: fa fa fa fa 04 fa fa fa fa fa fa fa 00 00 00 00 | ^ | ffff2000133d1c80: fa fa fa fa 00 fa fa fa fa fa fa fa 00 00 00 00 | ffff2000133d1d00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 Fix the splat by introducing a unsigned long 'zero_ul' and using that instead. Link: http://lkml.kernel.org/r/20190403153409.17307-1-will.deacon@arm.com Fixes: 32a5ad9c2285 ("sysctl: handle overflow for file-max") Signed-off-by: Will Deacon Acked-by: Christian Brauner Cc: Kees Cook Cc: Alexey Dobriyan Cc: Matteo Croce Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/sysctl.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sysctl.c b/kernel/sysctl.c index e5da394d1ca36..c9ec050bcf461 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -128,6 +128,7 @@ static int zero; static int __maybe_unused one = 1; static int __maybe_unused two = 2; static int __maybe_unused four = 4; +static unsigned long zero_ul; static unsigned long one_ul = 1; static unsigned long long_max = LONG_MAX; static int one_hundred = 100; @@ -1750,7 +1751,7 @@ static struct ctl_table fs_table[] = { .maxlen = sizeof(files_stat.max_files), .mode = 0644, .proc_handler = proc_doulongvec_minmax, - .extra1 = &zero, + .extra1 = &zero_ul, .extra2 = &long_max, }, {