Messages in this thread | | | Date | Wed, 18 Apr 2012 21:36:20 +0200 | From | Jan Kara <> | Subject | Re: jbd: NULL dereference on chown() |
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Hi,
On Wed 18-04-12 17:15:58, Sasha Levin wrote: > I've stumbled on the following after some fuzzing inside a KVM guest, > guest was running -next from today: Something really strange must have happened in your system. Instructions preceeding the faulting one look like (I've added some annotation): 15: f0 80 4b 01 40 lock orb $0x40,0x1(%rbx) set_buffer_jbd(bh); 1a: 4c 89 7b 40 mov %r15,0x40(%rbx) bh->b_private = jh; 1e: 49 89 1f mov %rbx,(%r15) jh->b_bh = bh; 21: f0 ff 43 60 lock incl 0x60(%rbx) get_bh(bh); 25: 4c 89 f8 mov %r15,%rax 28: 45 31 ff xor %r15d,%r15d 2b:* ff 40 08 incl 0x8(%rax) <-- trapping instruction jh->b_jcount++;
RAX at the moment of the fault is 0 (and also r15 from which we got the value is 0). The relevant chunk of the function looks like: jbd_lock_bh_journal_head(bh); if (buffer_jbd(bh)) { jh = bh2jh(bh); } else { J_ASSERT_BH(bh, (atomic_read(&bh->b_count) > 0) || (bh->b_page && bh->b_page->mapping));
if (!new_jh) { jbd_unlock_bh_journal_head(bh); goto repeat; }
jh = new_jh; new_jh = NULL; /* We consumed it */ set_buffer_jbd(bh); bh->b_private = jh; jh->b_bh = bh; get_bh(bh); BUFFER_TRACE(bh, "added journal_head"); } jh->b_jcount++; jbd_unlock_bh_journal_head(bh);
So we apparently saw buffer_jbd(), went through jh = bh2jh(bh) and oopsed on jh->b_jcount++. But I don't see how buffer_jbd() with bh->b_private == NULL can happen - we set and clear both together under bh_journal_head() lock. So either it was some random memory corruption or something really strange. But I'm afraid that unless you are able to reproduce the problem, I'm unable to debug this...
Honza
> [ 73.117530] BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 > [ 73.117534] IP: [<ffffffff81313a5e>] journal_add_journal_head+0x1be/0x220 > [ 73.117543] PGD 32327067 PUD 33d32067 PMD 0 > [ 73.117548] Oops: 0002 [#1] PREEMPT SMP > [ 73.117551] CPU 3 > [ 73.117555] Pid: 6964, comm: trinity Tainted: G W 3.4.0-rc3-next-20120418-sasha-dirty #85 > [ 73.117559] RIP: 0010:[<ffffffff81313a5e>] [<ffffffff81313a5e>] journal_add_journal_head+0x1be/0x220 > [ 73.117563] RSP: 0018:ffff880032195cf8 EFLAGS: 00010202 > [ 73.117565] RAX: 0000000000000000 RBX: ffff88003d0026c0 RCX: 0000000000000000 > [ 73.117568] RDX: 0000000000000000 RSI: ffff88003d0026c0 RDI: ffffffff8130cc6c > [ 73.117570] RBP: ffff880032195d28 R08: 0000000000000000 R09: 0000000000000000 > [ 73.117572] R10: 0000000000000000 R11: 0000000000000001 R12: ffff880032194000 > [ 73.117574] R13: 000000000000000e R14: ffff880032194000 R15: 0000000000000000 > [ 73.117577] FS: 00007f7615d4b700(0000) GS:ffff880035a00000(0000) knlGS:0000000000000000 > [ 73.117580] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 73.117582] CR2: 0000000000000008 CR3: 0000000031bb0000 CR4: 00000000000406e0 > [ 73.117590] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 73.117596] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 > [ 73.117598] Process trinity (pid: 6964, threadinfo ffff880032194000, task ffff880033cf8000) > [ 73.117600] Stack: > [ 73.117602] 00000000000003ff ffffffff82848140 ffff880035026000 ffff880035026000 > [ 73.117606] 0000000000000000 ffff880035026000 ffff880032195d48 ffffffff8130cc6c > [ 73.117611] ffffffff82848140 ffff88003d0026c0 ffff880032195d88 ffffffff812c5278 > [ 73.117615] Call Trace: > [ 73.117621] [<ffffffff8130cc6c>] journal_get_write_access+0x1c/0x50 > [ 73.117624] [<ffffffff812c5278>] __ext3_journal_get_write_access+0x28/0x60 > [ 73.117629] [<ffffffff812b7141>] ext3_reserve_inode_write+0x51/0xb0 > [ 73.117633] [<ffffffff812b71df>] ext3_mark_inode_dirty+0x3f/0x60 > [ 73.117636] [<ffffffff812b91bd>] ext3_setattr+0x12d/0x310 > [ 73.117642] [<ffffffff811fa3d9>] notify_change+0x209/0x330 > [ 73.117647] [<ffffffff811da0d8>] chown_common+0x98/0xc0 > [ 73.117650] [<ffffffff811dacdc>] sys_chown+0x5c/0x90 > [ 73.117657] [<ffffffff826a00bd>] system_call_fastpath+0x1a/0x1f > [ 73.117659] Code: a8 08 0f 84 95 fe ff ff e8 d0 98 38 01 e9 8b fe ff ff 0f 1f 00 f0 80 4b 01 40 4c 89 7b 40 49 89 1f f0 ff 43 60 4c 89 f8 45 31 ff <ff> 40 08 48 8b 03 a9 00 00 20 00 75 05 0f 0b 0f 1f 00 f0 80 63 > [ 73.117697] RIP [<ffffffff81313a5e>] journal_add_journal_head+0x1be/0x220 > [ 73.117701] RSP <ffff880032195cf8> > [ 73.117702] CR2: 0000000000000008 > [ 73.117706] ---[ end trace a307b3ed40206b4c ]--- >
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