| Message ID | 20190405065217.125140-1-houtao1@huawei.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | sysctl: redefine zero as a unsigned long | expand |
On Thu, Apr 4, 2019 at 11:48 PM Hou Tao <houtao1@huawei.com> wrote: > > We have got KASAN splat when tried to set /proc/sys/fs/file-max: > > BUG: KASAN: global-out-of-bounds in __do_proc_doulongvec_minmax+0x3e4/0x8f0 > Read of size 8 at addr ffff20000f9b2980 by task file-max.sh/36819 > > Call trace: > dump_backtrace+0x0/0x3f8 > show_stack+0x3c/0x60 > dump_stack+0x150/0x1a8 > print_address_description+0x2b8/0x5a0 > kasan_report+0x278/0x648 > __asan_load8+0x124/0x170 > __do_proc_doulongvec_minmax+0x3e4/0x8f0 > proc_doulongvec_minmax+0x80/0xa0 > proc_sys_call_handler+0x188/0x2a0 > proc_sys_write+0x5c/0x80 > __vfs_write+0x118/0x578 > vfs_write+0x184/0x418 > ksys_write+0xfc/0x1e8 > __arm64_sys_write+0x88/0xa8 > el0_svc_common+0x1a4/0x500 > el0_svc_handler+0xb8/0x180 > el0_svc+0x8/0xc > > The buggy address belongs to the variable: > zero+0x0/0x40 > > The cause is that proc_doulongvec_minmax() is trying to cast an int > pointer (namely &zero) to a unsigned long pointer, and dereferencing it. > > Although the warning seems does no harm, because zero will be placed > in a .bss section, but it's better to kill the KASAN warning by > redefining zero as a unsigned long, so it's OK whenever it is accessed > as an int or a a unsigned long. > > An alternative fix seems to be set the minimal value of file-max to be 1, > so one_ul can be used instead, but I'm not sure whether or not a file-max > with a value of zero has special purpose (e.g., prohibit the file-related > activities of all no-privileged users). > > Signed-off-by: Hou Tao <houtao1@huawei.com> Acked-by: Kees Cook <keescook@chromium.org> -Kees > --- > kernel/sysctl.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index e5da394d1ca3..03846e015013 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -124,7 +124,7 @@ static int sixty = 60; > > static int __maybe_unused neg_one = -1; > > -static int zero; > +static unsigned long zero; > static int __maybe_unused one = 1; > static int __maybe_unused two = 2; > static int __maybe_unused four = 4; > -- > 2.16.2.dirty >
On Fri, Apr 05, 2019 at 02:52:17PM +0800, Hou Tao wrote:
> We have got KASAN splat when tried to set /proc/sys/fs/file-max:
Matteo Croce already has a patch in-flight for this.
Hi, Cc Andrew for patch inclusion On 2019/4/6 0:27, Matthew Wilcox wrote: > On Fri, Apr 05, 2019 at 02:52:17PM +0800, Hou Tao wrote: >> We have got KASAN splat when tried to set /proc/sys/fs/file-max: > > Matteo Croce already has a patch in-flight for this. > > Yes, I find it now: https://lkml.org/lkml/2019/3/28/320. And the fix posted by Matteo has also been acked by Kees and has the Fixes tag. So Andrew, could you please take Matteo's patch in your tree ? Regards, Tao
diff --git a/kernel/sysctl.c b/kernel/sysctl.c index e5da394d1ca3..03846e015013 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -124,7 +124,7 @@ static int sixty = 60; static int __maybe_unused neg_one = -1; -static int zero; +static unsigned long zero; static int __maybe_unused one = 1; static int __maybe_unused two = 2; static int __maybe_unused four = 4;
We have got KASAN splat when tried to set /proc/sys/fs/file-max: BUG: KASAN: global-out-of-bounds in __do_proc_doulongvec_minmax+0x3e4/0x8f0 Read of size 8 at addr ffff20000f9b2980 by task file-max.sh/36819 Call trace: dump_backtrace+0x0/0x3f8 show_stack+0x3c/0x60 dump_stack+0x150/0x1a8 print_address_description+0x2b8/0x5a0 kasan_report+0x278/0x648 __asan_load8+0x124/0x170 __do_proc_doulongvec_minmax+0x3e4/0x8f0 proc_doulongvec_minmax+0x80/0xa0 proc_sys_call_handler+0x188/0x2a0 proc_sys_write+0x5c/0x80 __vfs_write+0x118/0x578 vfs_write+0x184/0x418 ksys_write+0xfc/0x1e8 __arm64_sys_write+0x88/0xa8 el0_svc_common+0x1a4/0x500 el0_svc_handler+0xb8/0x180 el0_svc+0x8/0xc The buggy address belongs to the variable: zero+0x0/0x40 The cause is that proc_doulongvec_minmax() is trying to cast an int pointer (namely &zero) to a unsigned long pointer, and dereferencing it. Although the warning seems does no harm, because zero will be placed in a .bss section, but it's better to kill the KASAN warning by redefining zero as a unsigned long, so it's OK whenever it is accessed as an int or a a unsigned long. An alternative fix seems to be set the minimal value of file-max to be 1, so one_ul can be used instead, but I'm not sure whether or not a file-max with a value of zero has special purpose (e.g., prohibit the file-related activities of all no-privileged users). Signed-off-by: Hou Tao <houtao1@huawei.com> --- kernel/sysctl.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)