Re: [PATCH] audit: grab a reference to context->pwd when it's cached

On Mon, Oct 8, 2012 at 5:23 AM, Jeff Layton <jlayton(a)redhat.com&gt; wrote: > On Fri, 5 Oct 2012 12:41:46 -0700 > Peter Moody <pmoody(a)google.com&gt; wrote: > >> On Fri, Oct 5, 2012 at 10:04 AM, Peter Moody <pmoody(a)google.com&gt; wrote: >> > On Fri, Oct 5, 2012 at 9:15 AM, Jeff Layton <jlayton(a)redhat.com&gt; wrote: >> > >> >>> >> >>> ------------[ cut here ]------------ >> >>> kernel BUG at fs/buffer.c:1220! >> >>> invalid opcode: 0000 [#1] SMP >> >>> CPU 0 >> >>> Pid: 3683, comm: a.out Not tainted 3.5.0 #3 >> >>> RIP: e030:[<ffffffff816a99f4>] [<ffffffff816a99f4>] >> >>> check_irqs_on.part.8+0x4/0x6 >> >>> RSP: e02b:ffff8807b156dc28 EFLAGS: 00010046 >> >>> RAX: ffff8807d0dd0000 RBX: ffff8807a7d6df28 RCX: 0000000005883396 >> >>> RDX: 0000000000001000 RSI: 0000000005883396 RDI: ffff8807cfc0c000 >> >>> RBP: ffff8807b156dc28 R08: 0000000000000001 R09: ffff8807a7d6de50 >> >>> R10: f83a2b0a359bf007 R11: 0000000000000000 R12: ffff8807a7d6de54 >> >>> R13: ffff8807a7d6de80 R14: ffff8807cfc1f120 R15: 0000000005883396 >> >>> FS: 00007f97164ec700(0000) GS:ffff8807ffc00000(0063) knlGS:0000000000000000 >> >>> CS: e033 DS: 002b ES: 002b CR0: 000000008005003b >> >>> CR2: 00000000f76ca3b0 CR3: 00000007bbb53000 CR4: 0000000000002660 >> >>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 >> >>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400 >> >>> Process a.out (pid: 3683, threadinfo ffff8807b156c000, task ffff8807bbae8000) >> >>> Stack: >> >>> ffff8807b156dc98 ffffffff8116a099 ffff8807b59f3000 ffff8807b156dd30 >> >>> ffff8807b156dd60 ffff8807b156de78 ffff8807b156dc78 ffffffff816af231 >> >>> ffff8807b156dcd8 ffff8807a7d6e538 ffff8807a7d6df28 ffff8807a7d6de54 >> >>> Call Trace: >> >>> [<ffffffff8116a099>] __find_get_block+0x1f9/0x200 >> >>> [<ffffffff816af231>] ? down_read+0x11/0x30 >> >>> [<ffffffff811d1405>] ext3_clear_blocks+0x75/0x140 >> >>> [<ffffffff811d15dc>] ext3_free_data+0x10c/0x150 >> >>> [<ffffffff811e2061>] ? ext3_journal_start_sb+0x31/0x60 >> >>> [<ffffffff811d1cb5>] ext3_truncate+0x4a5/0x600 >> >>> [<ffffffff8123d5b8>] ? journal_start+0xb8/0x100 >> >>> [<ffffffff8106f406>] ? bit_waitqueue+0x16/0xc0 >> >>> [<ffffffff811d4598>] ext3_evict_inode+0x248/0x2c0 >> >>> [<ffffffff81153b9a>] evict+0xaa/0x1b0 >> >>> [<ffffffff81154843>] iput+0x103/0x210 >> >>> [<ffffffff8114fc88>] dentry_iput+0x88/0xd0 >> >>> [<ffffffff811505ec>] dput+0x12c/0x250 >> >>> [<ffffffff81146275>] path_put+0x15/0x30 >> >>> [<ffffffff810b2f35>] __audit_syscall_exit+0x2e5/0x460 >> >>> [<ffffffff816b30be>] sysexit_audit+0x29/0x5b >> >>> Code: 04 00 00 4c 8d 88 c0 02 00 00 31 c0 e8 5f da ff ff 48 85 db 74 >> >>> 0c 80 43 5c 01 48 89 df e8 d5 >> >>> 6a aa ff 5b 41 5c 5d c3 55 48 89 e5 <0f> 0b 55 48 89 e5 0f 0b 55 48 89 >> >>> e5 0f 0b 55 48 89 e5 41 54 53 >> >>> RIP [<ffffffff816a99f4>] check_irqs_on.part.8+0x4/0x6 >> >>> RSP <ffff8807b156dc28> >> >>> ---[ end trace 8d09f8cfbb601c14 ]--- >> >>> >> >>> >> >> >> >> I don't see a function called sysexit_audit in 3.5. I assume that's >> >> created via some sort of macro goop? >> > >> > It looks like it's defined in arch/x86/kernel/entry_32.S >> > >> > my asm is non-existent, but it looks like it's calling >> > __audit_syscall_exit and the disabling interrupts. >> > >> >> Could this be a xen specific problem? >> > >> > It could be. I asked the xen folks about this and they felt that it >> > was unlikely that the bug itself was their >> > (http://lists.xen.org/archives/html/xen-devel/2012-08/msg01052.html, >> > specifically http://lists.xen.org/archives/html/xen-devel/2012-08/msg01127.html) >> > >> > xen could definitely be doing something wonky with irqs though. >> > >> >> Might be interesting to add a >> >> check for irqs being disabled early in __audit_syscall_exit and see >> >> whether its doing that universally in its syscall exit routine? >> > >> > I'll try this, thanks. >> >> So, I've added WARN_ON(irqs_disabled()) in various spots in the >> audit_syscall_exit path all the way up to the path_put in >> audit_free_names() that ends up triggering this and prior to Oops'ing, >> I don't see anything. >> >> Post oops, I get lots of messages like: >> >> ------------[ cut here ]------------ >> WARNING: at kernel/auditsc.c:1021 audit_free_names+0xb0/0xdb() >> Pid: 3981, comm: python2.6 Tainted: G D W 3.2.5-at17-ganetixenu #31 >> Call Trace: >> [<ffffffff81693483>] ? audit_free_names+0xb0/0xdb >> [<ffffffff8105f405>] warn_slowpath_common+0x75/0xb0 >> [<ffffffff8105f535>] warn_slowpath_null+0x15/0x20 >> [<ffffffff81693483>] audit_free_names+0xb0/0xdb >> [<ffffffff810ac629>] audit_syscall_exit+0x139/0x1e0 >> [<ffffffff8169fd6a>] sysexit_audit+0x21/0x5f >> ---[ end trace ec7a15dbe40eaf1d ]--- >> ------------[ cut here ]------------ >> WARNING: at kernel/auditsc.c:1021 audit_free_names+0xb0/0xdb() >> Pid: 3981, comm: python2.6 Tainted: G D W 3.2.5-at17-ganetixenu #31 >> Call Trace: >> [<ffffffff81693483>] ? audit_free_names+0xb0/0xdb >> [<ffffffff8105f405>] warn_slowpath_common+0x75/0xb0 >> [<ffffffff8105f535>] warn_slowpath_null+0x15/0x20 >> [<ffffffff81693483>] audit_free_names+0xb0/0xdb >> [<ffffffff810ac629>] audit_syscall_exit+0x139/0x1e0 >> [<ffffffff8169fd6a>] sysexit_audit+0x21/0x5f >> ---[ end trace ec7a15dbe40eaf1e ]--- >> >> where that python command is a python par file that may be doing some >> funny unlinking as well. I haven't tracked it down. >> >> thoughts? does this not look like a bug in audit; maybe something >> somewhere else is disabling interrupts? >> > > I'm not sure whether it's a bug in audit or not. Tracking down what's > disabling interrupts here is probably the key though... Yeah. I'm trying to get a reproducer to work on a different version of Xen. > So I'm guessing the WARN_ON above was in audit_free_names. Was there a > similar WARN_ON in audit_syscall_exit that did not fire? Correct. I booted a few kernels with the WARN_ON successively further down the stack in audit land and it only started firing after BUG_ON() in fs/buffer.c Thanks for looking into this.

Cheers, peter -- Peter Moody Google 1.650.253.7306 Security Engineer pgp:0xC3410038