‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Sunday, January 13, 2019 10:52 PM, Douglas Gilbert <dgilbert@xxxxxxxxxxxx> wrote: > On 2019-01-13 10:07 p.m., Esme wrote: > > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ > > On Sunday, January 13, 2019 9:33 PM, Qian Cai cai@xxxxxx 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@xxxxxxxxxxxxxx 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@xxxxxxxxxxxxx > > > > > > > Tested-by: Joey Pabalinas joeypabalinas@xxxxxxxxx > > > > > > > Signed-off-by: Qian Cai cai@xxxxxx > > > > > > > > > > > > Tested-by: David Lechner david@xxxxxxxxxxxxxx > > > > > > 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. Esme
