Re: [PATCH v2 4/7] fs/proc/task_mmu.c: shift mm_access() from m_start() to proc_maps_open()

From: Kirill A. Shutemov
Date: Wed Dec 03 2014 - 09:42:40 EST

On Tue, Aug 05, 2014 at 09:46:55PM +0200, Oleg Nesterov wrote:
> A simple test-case from Kirill Shutemov
>
> cat /proc/self/maps >/dev/null
> chmod +x /proc/self/net/packet
> exec /proc/self/net/packet
>
> makes lockdep unhappy, cat/exec take seq_file->lock + cred_guard_mutex in
> the opposite order.

Oleg, I see it again with almost the same test-case:

cat /proc/self/stack >/dev/null
chmod +x /proc/self/net/packet
exec /proc/self/net/packet

Looks like bunch of proc files were converted to use seq_file by Alexey
Dobriyan around the same time you've fixed the issue for /proc/pid/maps.

More generic test-case:

find /proc/self/ -type f -exec dd if='{}' of=/dev/null bs=1 count=1 ';' 2>/dev/null
chmod +x /proc/self/net/packet
exec /proc/self/net/packet

David, any justification for allowing chmod +x for files under
/proc/pid/net?

[ 2.042212] ======================================================
[ 2.042930] [ INFO: possible circular locking dependency detected ]
[ 2.043648] 3.18.0-rc7-00003-g3a18ca061311-dirty #237 Not tainted
[ 2.044350] -------------------------------------------------------
[ 2.045054] sh/94 is trying to acquire lock:
[ 2.045546] (&p->lock){+.+.+.}, at: [<ffffffff811e12fd>] seq_read+0x3d/0x3e0
[ 2.045781]
[ 2.045781] but task is already holding lock:
[ 2.045781] (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811c0e3d>] prepare_bprm_creds+0x2d/0x90
[ 2.045781]
[ 2.045781] which lock already depends on the new lock.
[ 2.045781]
[ 2.045781]
[ 2.045781] the existing dependency chain (in reverse order) is:
[ 2.045781]
-> #1 (&sig->cred_guard_mutex){+.+.+.}:
[ 2.045781] [<ffffffff810a6e99>] __lock_acquire+0x4d9/0xd40
[ 2.045781] [<ffffffff810a7ff2>] lock_acquire+0xd2/0x2a0
[ 2.045781] [<ffffffff81849da6>] mutex_lock_killable_nested+0x66/0x460
[ 2.045781] [<ffffffff81229de4>] lock_trace+0x24/0x70
[ 2.045781] [<ffffffff81229e8f>] proc_pid_stack+0x5f/0xe0
[ 2.045781] [<ffffffff81227244>] proc_single_show+0x54/0xa0
[ 2.045781] [<ffffffff811e13a0>] seq_read+0xe0/0x3e0
[ 2.045781] [<ffffffff811b9377>] vfs_read+0x97/0x180
[ 2.045781] [<ffffffff811b9f5d>] SyS_read+0x4d/0xc0
[ 2.045781] [<ffffffff8184e492>] system_call_fastpath+0x12/0x17
[ 2.045781]
-> #0 (&p->lock){+.+.+.}:
[ 2.045781] [<ffffffff810a389f>] validate_chain.isra.36+0xfff/0x1400
[ 2.045781] [<ffffffff810a6e99>] __lock_acquire+0x4d9/0xd40
[ 2.045781] [<ffffffff810a7ff2>] lock_acquire+0xd2/0x2a0
[ 2.045781] [<ffffffff81849629>] mutex_lock_nested+0x69/0x3c0
[ 2.045781] [<ffffffff811e12fd>] seq_read+0x3d/0x3e0
[ 2.045781] [<ffffffff81226428>] proc_reg_read+0x48/0x70
[ 2.045781] [<ffffffff811b9377>] vfs_read+0x97/0x180
[ 2.045781] [<ffffffff811bf1a8>] kernel_read+0x48/0x60
[ 2.045781] [<ffffffff811bfb2c>] prepare_binprm+0xdc/0x180
[ 2.045781] [<ffffffff811c139a>] do_execve_common.isra.29+0x4fa/0x960
[ 2.045781] [<ffffffff811c1818>] do_execve+0x18/0x20
[ 2.045781] [<ffffffff811c1b05>] SyS_execve+0x25/0x30
[ 2.045781] [<ffffffff8184ea49>] stub_execve+0x69/0xa0
[ 2.045781]
[ 2.045781] other info that might help us debug this:
[ 2.045781]
[ 2.045781] Possible unsafe locking scenario:
[ 2.045781]
[ 2.045781] CPU0 CPU1
[ 2.045781] ---- ----
[ 2.045781] lock(&sig->cred_guard_mutex);
[ 2.045781] lock(&p->lock);
[ 2.045781] lock(&sig->cred_guard_mutex);
[ 2.045781] lock(&p->lock);
[ 2.045781]
[ 2.045781] *** DEADLOCK ***
[ 2.045781]
[ 2.045781] 1 lock held by sh/94:
[ 2.045781] #0: (&sig->cred_guard_mutex){+.+.+.}, at: [<ffffffff811c0e3d>] prepare_bprm_creds+0x2d/0x90
[ 2.045781]
[ 2.045781] stack backtrace:
[ 2.045781] CPU: 0 PID: 94 Comm: sh Not tainted 3.18.0-rc7-00003-g3a18ca061311-dirty #237
[ 2.045781] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org 04/01/2014
[ 2.045781] ffffffff82a48d50 ffff88085427bad8 ffffffff81844a85 0000000000000cac
[ 2.045781] ffffffff82a654a0 ffff88085427bb28 ffffffff810a1b03 0000000000000000
[ 2.045781] ffff88085427bb68 ffff88085427bb28 ffff8808547f1500 ffff8808547f1c40
[ 2.045781] Call Trace:
[ 2.045781] [<ffffffff81844a85>] dump_stack+0x4e/0x68
[ 2.045781] [<ffffffff810a1b03>] print_circular_bug+0x203/0x310
[ 2.045781] [<ffffffff810a389f>] validate_chain.isra.36+0xfff/0x1400
[ 2.045781] [<ffffffff8108fa76>] ? local_clock+0x16/0x30
[ 2.045781] [<ffffffff810a6e99>] __lock_acquire+0x4d9/0xd40
[ 2.045781] [<ffffffff810a7ff2>] lock_acquire+0xd2/0x2a0
[ 2.045781] [<ffffffff811e12fd>] ? seq_read+0x3d/0x3e0
[ 2.045781] [<ffffffff81849629>] mutex_lock_nested+0x69/0x3c0
[ 2.045781] [<ffffffff811e12fd>] ? seq_read+0x3d/0x3e0
[ 2.045781] [<ffffffff8108f9f8>] ? sched_clock_cpu+0x98/0xc0
[ 2.045781] [<ffffffff811e12fd>] ? seq_read+0x3d/0x3e0
[ 2.045781] [<ffffffff814050b9>] ? lockref_put_or_lock+0x29/0x40
[ 2.045781] [<ffffffff811e12fd>] seq_read+0x3d/0x3e0
[ 2.045781] [<ffffffff814050b9>] ? lockref_put_or_lock+0x29/0x40
[ 2.045781] [<ffffffff81226428>] proc_reg_read+0x48/0x70
[ 2.045781] [<ffffffff811b9377>] vfs_read+0x97/0x180
[ 2.045781] [<ffffffff811bf1a8>] kernel_read+0x48/0x60
[ 2.045781] [<ffffffff811bfb2c>] prepare_binprm+0xdc/0x180
[ 2.045781] [<ffffffff811c139a>] do_execve_common.isra.29+0x4fa/0x960
[ 2.092142] tsc: Refined TSC clocksource calibration: 2693.484 MHz
[ 2.045781] [<ffffffff811c0fd3>] ? do_execve_common.isra.29+0x133/0x960
[ 2.045781] [<ffffffff8184f04d>] ? retint_swapgs+0xe/0x13
[ 2.045781] [<ffffffff811c1818>] do_execve+0x18/0x20
[ 2.045781] [<ffffffff811c1b05>] SyS_execve+0x25/0x30
[ 2.045781] [<ffffffff8184ea49>] stub_execve+0x69/0xa0
--
Kirill A. Shutemov
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