On Sat, Feb 20, 2016 at 4:21 AM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Fri, Feb 19, 2016 at 08:32:10PM +0100, Dmitry Vyukov wrote: >> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000050 > > NULL inode->i_sb, by the look of the offset, but I really don't understand > where the hell is that code doing (or how is that instruction going to > generate dereferencing of 0x50, for that matter). > >> I've hit another GPF in atime_needs_update, but this time from SyS_openat: >> >> kasan: GPF could be caused by NULL-ptr deref or user memory >> accessgeneral protection fault: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN >> Modules linked in: >> CPU: 0 PID: 20147 Comm: syz-executor Not tainted 4.5.0-rc4+ #329 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011 >> task: ffff88005f154740 ti: ffff88005f048000 task.ti: ffff88005f048000 >> RIP: 0010:[<ffffffff81818b5d>] [<ffffffff81818b5d>] >> atime_needs_update+0x2d/0x460 >> RSP: 0018:ffff88005f04fa48 EFLAGS: 00010203 >> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffff88005f04fd88 >> RDX: 0000000000000001 RSI: 0000000000000000 RDI: 000000000000000c >> RBP: ffff88005f04fa70 R08: 0000000000000001 R09: 0000000000000000 >> R10: 0000000000000000 R11: 0000000000000001 R12: ffff88005f04fd98 >> R13: 0000000000000000 R14: ffff88005f04fd98 R15: ffff88005f04fd78 >> FS: 00007f612639b700(0000) GS:ffff88003ec00000(0000) knlGS:0000000000000000 >> CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b >> CR2: 000000002003ef84 CR3: 000000006073e000 CR4: 00000000000006f0 >> Stack: >> ffff88005f04fd40 ffff88005f04fe08 0000000000000000 ffff88005f04fd98 >> ffff88005f04fd78 ffff88005f04fab8 ffffffff817e5572 ffff88005f04fd78 >> ffff88002bcf02f8 0000000000000001 0000000000000000 ffff88002bcf02f8 >> Call Trace: >> [< inline >] get_link fs/namei.c:1006 >> [<ffffffff817e5572>] trailing_symlink+0x142/0x760 fs/namei.c:2094 >> [<ffffffff817ec531>] path_openat+0xbc1/0x5e30 fs/namei.c:3389 >> [<ffffffff817f4fde>] do_filp_open+0x18e/0x250 fs/namei.c:3421 >> [<ffffffff817b970c>] do_sys_open+0x1fc/0x420 fs/open.c:1022 >> [< inline >] SYSC_openat fs/open.c:1049 >> [<ffffffff817b99a0>] SyS_openat+0x30/0x40 fs/open.c:1043 >> [<ffffffff86662636>] entry_SYSCALL_64_fastpath+0x16/0x7a >> arch/x86/entry/entry_64.S:185 >> Code: 89 e5 41 57 41 56 41 55 41 54 49 89 fc 53 48 89 f3 e8 c8 32 d5 >> ff 48 8d 7b 0c 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> >> b6 14 02 48 89 f8 83 e0 07 83 c0 03 38 d0 7c 08 84 d2 0f 85 >> RIP [<ffffffff81818b5d>] atime_needs_update+0x2d/0x460 fs/inode.c:1611 >> RSP <ffff88005f04fa48> > > What was the fault address here and what config are you using for those > builds? This is with CONFIG_KASAN. GPF happens on shadow check for NULL address. In both cases: RAX: dffffc0000000000 RDX: 0000000000000001 where dffffc0000000000 is shadow base and 0000000000000001 is offset. So the original memory access was to range [8-16) (i.e. NULL with small offset). -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
