On Wed, Oct 31, 2018 at 06:46:16AM -0400, Kyungtae Kim wrote: > We report a crash in v4.19-rc2 (and the latest kernel as well): > > kernel config: https://kt0755.github.io/etc/config_v2-4.19 > repro: https://kt0755.github.io/etc/repro.1e3e9.c > > unit_set() lacks the bounds checking for an integer variable n, > which causes integer overflow when it is equal to INT_MAX. > idr_alloc() does revert the overflowed n+1 to INT_MAX, so everything works as expected in practive. But sure, the code, as it is, looks wrong. > ======================================================= > UBSAN: Undefined behaviour in drivers/net/ppp/ppp_generic.c:3246:9 > signed integer overflow: > 2147483647 + 1 cannot be represented in type 'int' > CPU: 0 PID: 7676 Comm: syz-executor4 Not tainted 4.19.0-rc2 #1 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0xd2/0x148 lib/dump_stack.c:113 > ubsan_epilogue+0x12/0x94 lib/ubsan.c:159 > handle_overflow+0x1cf/0x21a lib/ubsan.c:190 > __ubsan_handle_add_overflow+0x2a/0x31 lib/ubsan.c:198 > unit_set drivers/net/ppp/ppp_generic.c:3246 [inline] > ppp_unit_register drivers/net/ppp/ppp_generic.c:979 [inline] > ppp_dev_configure+0xbd8/0xd50 drivers/net/ppp/ppp_generic.c:1049 > ppp_create_interface drivers/net/ppp/ppp_generic.c:3013 [inline] > ppp_unattached_ioctl drivers/net/ppp/ppp_generic.c:848 [inline] > ppp_ioctl+0x1652/0x27f0 drivers/net/ppp/ppp_generic.c:601 > vfs_ioctl fs/ioctl.c:46 [inline] > do_vfs_ioctl+0x1c0/0x1150 fs/ioctl.c:687 > ksys_ioctl+0x9e/0xb0 fs/ioctl.c:702 > __do_sys_ioctl fs/ioctl.c:709 [inline] > __se_sys_ioctl fs/ioctl.c:707 [inline] > __x64_sys_ioctl+0x7e/0xc0 fs/ioctl.c:707 > do_syscall_64+0xc4/0x510 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x4497b9 > Code: e8 8c 9f 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 48 89 f8 48 > 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d > 01 f0 ff ff 0f 83 9b 6b fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f67b6f92c68 EFLAGS: 00000246 ORIG_RAX: 0000000000000010 > RAX: ffffffffffffffda RBX: 00007f67b6f936cc RCX: 00000000004497b9 > RDX: 0000000020000080 RSI: 00000000c004743e RDI: 0000000000000013 > RBP: 000000000071bea0 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff > R13: 0000000000005598 R14: 00000000006ed638 R15: 00007f67b6f93700 > ====================================================== > > A simple patch below is provided. > Note that in this control flow, negative n is already > filtered out (drivers/net/ppp/ppp_generic.c:965). > > --- a/drivers/net/ppp/ppp_generic.c > +++ b/drivers/net/ppp/ppp_generic.c > @@ -3243,6 +3243,9 @@ static int unit_set(struct idr *p, void *ptr, int n) > { > int unit; > > + if (n == INT_MAX) > + return -EINVAL; > + > unit = idr_alloc(p, ptr, n, n + 1, GFP_KERNEL); > if (unit == -ENOSPC) > unit = -EINVAL; > What about using idr_alloc_u32() instead? This way we could safely continue to accept INT_MAX, without relying on idr_alloc() internal safeguards.
