Messages in this thread | | | Date | Wed, 3 Apr 2019 18:24:15 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] kernel/sysctl.c: Fix out-of-bounds access when setting file-max |
| |
Hi Christian,
On Wed, Apr 03, 2019 at 05:40:45PM +0200, Christian Brauner wrote: > On Wed, Apr 03, 2019 at 04:34:09PM +0100, Will Deacon wrote: > > 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. > > > > Fixes: 32a5ad9c2285 ("sysctl: handle overflow for file-max") > > Cc: Christian Brauner <christian@brauner.io> > > Cc: Kees Cook <keescook@chromium.org> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Signed-off-by: Will Deacon <will.deacon@arm.com> > > Hey Will, thanks! For the record, there's another patch by Matteo (Cced) > for the same thing: > https://lore.kernel.org/lkml/20190328130306.25384-1-mcroce@redhat.com/
Oops, sorry, I didn't spot that. I just ran into this while I was using KASAN to investigate a different issue and quickly sent out a fix.
> He's proposing a slightly different version for the fix. I don't care > very much but I like that you've used the explicit unsigned long so: > > Acked-by: Christian Brauner <christian@brauner.io> > > Thanks to both of you for fixing this!
I'm also not bothered about which patch gets in, as long as the problem is fixed. I assume somebody will pick up one of them...
Will
| |