From 701e054e0c2db82359f0454c7ed4fd24346d52eb Mon Sep 17 00:00:00 2001 From: Vasily Tarasov Date: Sat, 25 Nov 2006 11:09:22 -0800 Subject: [PATCH] [PATCH] mounstats NULL pointer dereference OpenVZ developers team has encountered the following problem in 2.6.19-rc6 kernel. After some seconds of running script while [[ 1 ]] do find /proc -name mountstats | xargs cat done this Oops appears: BUG: unable to handle kernel NULL pointer dereference at virtual address 00000010 printing eip: c01a6b70 *pde = 00000000 Oops: 0000 [#1] SMP Modules linked in: xt_length ipt_ttl xt_tcpmss ipt_TCPMSS iptable_mangle iptable_filter xt_multiport xt_limit ipt_tos ipt_REJECT ip_tables x_tables parport_pc lp parport sunrpc af_packet thermal processor fan button battery asus_acpi ac ohci_hcd ehci_hcd usbcore i2c_nforce2 i2c_core tg3 floppy pata_amd ide_cd cdrom sata_nv libata CPU: 1 EIP: 0060:[] Not tainted VLI EFLAGS: 00010246 (2.6.19-rc6 #2) EIP is at mountstats_open+0x70/0xf0 eax: 00000000 ebx: e6247030 ecx: e62470f8 edx: 00000000 esi: 00000000 edi: c01a6b00 ebp: c33b83c0 esp: f4105eb4 ds: 007b es: 007b ss: 0068 Process cat (pid: 6044, ti=f4105000 task=f4104a70 task.ti=f4105000) Stack: c33b83c0 c04ee940 f46a4a80 c33b83c0 e4df31b4 c01a6b00 f4105000 c0169231 e4df31b4 c33b83c0 c33b83c0 f4105f20 00000003 f4105000 c0169445 f2503cf0 f7f8c4c0 00008000 c33b83c0 00000000 00008000 c0169350 f4105f20 00008000 Call Trace: [] mountstats_open+0x0/0xf0 [] __dentry_open+0x181/0x250 [] nameidata_to_filp+0x35/0x50 [] do_filp_open+0x50/0x60 [] seq_read+0xc6/0x300 [] get_unused_fd+0x31/0xc0 [] do_sys_open+0x63/0x110 [] sys_open+0x27/0x30 [] sysenter_past_esp+0x56/0x79 ======================= Code: 45 74 8b 54 24 20 89 44 24 08 8b 42 f0 31 d2 e8 47 cb f8 ff 85 c0 89 c3 74 51 8d 80 a0 04 00 00 e8 46 06 2c 00 8b 83 48 04 00 00 <8b> 78 10 85 ff 74 03 f0 ff 07 b0 01 86 83 a0 04 00 00 f0 ff 4b EIP: [] mountstats_open+0x70/0xf0 SS:ESP 0068:f4105eb4 The problem is that task->nsproxy can be equal NULL for some time during task exit. This patch fixes the BUG. Signed-off-by: Vasily Tarasov Cc: Herbert Poetzl Cc: "Serge E. Hallyn" Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/base.c | 3 ++- include/linux/nsproxy.h | 4 +++- 2 files changed, 5 insertions(+), 2 deletions(-) diff --git a/fs/proc/base.c b/fs/proc/base.c index 8df27401d29..795319c54f7 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -442,7 +442,8 @@ static int mountstats_open(struct inode *inode, struct file *file) if (task) { task_lock(task); - namespace = task->nsproxy->namespace; + if (task->nsproxy) + namespace = task->nsproxy->namespace; if (namespace) get_namespace(namespace); task_unlock(task); diff --git a/include/linux/nsproxy.h b/include/linux/nsproxy.h index f6baecdeecd..971d1c6dfc4 100644 --- a/include/linux/nsproxy.h +++ b/include/linux/nsproxy.h @@ -45,8 +45,10 @@ static inline void exit_task_namespaces(struct task_struct *p) { struct nsproxy *ns = p->nsproxy; if (ns) { - put_nsproxy(ns); + task_lock(p); p->nsproxy = NULL; + task_unlock(p); + put_nsproxy(ns); } } #endif -- 2.41.1