Messages in this thread | | | Subject | Re: [PATCH v2] rbtree: fix the red root | From | Douglas Gilbert <> | Date | Sun, 13 Jan 2019 23:52:06 -0500 |
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On 2019-01-13 10:59 p.m., Esme wrote: > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ > On Sunday, January 13, 2019 10:52 PM, Douglas Gilbert <dgilbert@interlog.com> wrote: > >> On 2019-01-13 10:07 p.m., Esme wrote: >> >>> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ >>> On Sunday, January 13, 2019 9:33 PM, Qian Cai cai@lca.pw wrote: >>> >>>> On 1/13/19 9:20 PM, David Lechner wrote: >>>> >>>>> On 1/11/19 8:58 PM, Michel Lespinasse wrote: >>>>> >>>>>> On Fri, Jan 11, 2019 at 3:47 PM David Lechner david@lechnology.com wrote: >>>>>> >>>>>>> On 1/11/19 2:58 PM, Qian Cai wrote: >>>>>>> >>>>>>>> A GPF was reported, >>>>>>>> kasan: CONFIG_KASAN_INLINE enabled >>>>>>>> kasan: GPF could be caused by NULL-ptr deref or user memory access >>>>>>>> general protection fault: 0000 [#1] SMP KASAN >>>>>>>> kasan_die_handler.cold.22+0x11/0x31 >>>>>>>> notifier_call_chain+0x17b/0x390 >>>>>>>> atomic_notifier_call_chain+0xa7/0x1b0 >>>>>>>> notify_die+0x1be/0x2e0 >>>>>>>> do_general_protection+0x13e/0x330 >>>>>>>> general_protection+0x1e/0x30 >>>>>>>> rb_insert_color+0x189/0x1480 >>>>>>>> create_object+0x785/0xca0 >>>>>>>> kmemleak_alloc+0x2f/0x50 >>>>>>>> kmem_cache_alloc+0x1b9/0x3c0 >>>>>>>> getname_flags+0xdb/0x5d0 >>>>>>>> getname+0x1e/0x20 >>>>>>>> do_sys_open+0x3a1/0x7d0 >>>>>>>> __x64_sys_open+0x7e/0xc0 >>>>>>>> do_syscall_64+0x1b3/0x820 >>>>>>>> entry_SYSCALL_64_after_hwframe+0x49/0xbe >>>>>>>> It turned out, >>>>>>>> gparent = rb_red_parent(parent); >>>>>>>> tmp = gparent->rb_right; <-- GPF was triggered here. >>>>>>>> Apparently, "gparent" is NULL which indicates "parent" is rbtree's root >>>>>>>> which is red. Otherwise, it will be treated properly a few lines above. >>>>>>>> /* >>>>>>>> * If there is a black parent, we are done. >>>>>>>> * Otherwise, take some corrective action as, >>>>>>>> * per 4), we don't want a red root or two >>>>>>>> * consecutive red nodes. >>>>>>>> */ >>>>>>>> if(rb_is_black(parent)) >>>>>>>> break; >>>>>>>> Hence, it violates the rule #1 (the root can't be red) and need a fix >>>>>>>> up, and also add a regression test for it. This looks like was >>>>>>>> introduced by 6d58452dc06 where it no longer always paint the root as >>>>>>>> black. >>>>>>>> Fixes: 6d58452dc06 (rbtree: adjust root color in rb_insert_color() only >>>>>>>> when necessary) >>>>>>>> Reported-by: Esme esploit@protonmail.ch >>>>>>>> Tested-by: Joey Pabalinas joeypabalinas@gmail.com >>>>>>>> Signed-off-by: Qian Cai cai@lca.pw >>>>>>> >>>>>>> Tested-by: David Lechner david@lechnology.com >>>>>>> FWIW, this fixed the following crash for me: >>>>>>> Unable to handle kernel NULL pointer dereference at virtual address 00000004 >>>>>> >>>>>> Just to clarify, do you have a way to reproduce this crash without the fix ? >>>>> >>>>> I am starting to suspect that my crash was caused by some new code >>>>> in the drm-misc-next tree that might be causing a memory corruption. >>>>> It threw me off that the stack trace didn't contain anything related >>>>> to drm. >>>>> See: https://patchwork.freedesktop.org/patch/276719/ >>>> >>>> It may be useful for those who could reproduce this issue to turn on those >>>> memory corruption debug options to narrow down a bit. >>>> CONFIG_DEBUG_PAGEALLOC=y >>>> CONFIG_DEBUG_PAGEALLOC_ENABLE_DEFAULT=y >>>> CONFIG_KASAN=y >>>> CONFIG_KASAN_GENERIC=y >>>> CONFIG_SLUB_DEBUG_ON=y >>> >>> I have been on SLAB, I configured SLAB DEBUG with a fresh pull from github. Linux syzkaller 5.0.0-rc2 #9 SMP Sun Jan 13 21:57:40 EST 2019 x86_64 >>> ... >>> In an effort to get a different stack into the kernel, I felt that nothing works better than fork bomb? :) >>> Let me know if that helps. >>> root@syzkaller:~# gcc -o test3 test3.c >>> root@syzkaller:~# while : ; do ./test3 & done >> >> And is test3 the same multi-threaded program that enters the kernel via >> /dev/sg0 and then calls SCSI_IOCTL_SEND_COMMAND which goes to the SCSI >> mid-level and thence to the block layer? >> >> And please remind me, does it also fail on lk 4.20.2 ? >> >> Doug Gilbert > > Yes, the same C repro from the earlier thread. It was a 4.20.0 kernel where it was first detected. I can move to 4.20.2 and see if that changes anything.
Hi, I don't think there is any need to check lk 4.20.2 (as it would be very surprising if it didn't also have this "feature").
More interesting might be: has "test3" been run on lk 4.19 or any earlier kernel?
Doug Gilbert
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