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Date: Wed, 27 Dec 2006 16:42:23 +0300
From: Alexey Dobriyan <adobriyan@openvz.org>
To: linux-kernel@vger.kernel.org
Cc: devel@openvz.org
Subject: Racy /proc creations interfaces
Message-ID: <20061227134223.GA6044@localhost.sw.ru>
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1. Not setting ->owner for your favourite /proc file is oopsable.

	$ while true; do cat /proc/fs/xfs/stat 1>/dev/null 2>/dev/null; done
	# while true; do modprobe xfs; rmmod xfs; done

BUG: unable to handle kernel paging request at virtual address fc281049
 printing eip:
fc281049
*pde = 37ca7067
Oops: 0000 [#1]
Modules linked in: af_packet ohci_hcd e1000 ehci_hcd uhci_hcd usbcore
CPU:    0
EIP:    0060:[<fc281049>]    Not tainted VLI
EFLAGS: 00010282   (2.6.19 #2)
EIP is at 0xfc281049
eax: f0705000   ebx: 00000000   ecx: 00000105   edx: f1e5ff68
esi: f0705000   edi: fc281049   ebp: 00000c00   esp: f1e5ff4c
ds: 007b   es: 007b   ss: 0068
Process cat (pid: 32588, ti=f1e5e000 task=f4377030 task.ti=f1e5e000)
Stack: c0177d9c 00000c00 f1e5ff6c 00000000 00001000 08051000 f7ccc240 00000000 
       00000000 edbe82c0 00001000 08051000 f1e5ffa4 c0149f05 f1e5ffa4 c0177be5 
       edbe82c0 fffffff7 08051000 f1e5e000 c014a26d f1e5ffa4 00000105 00000000 
Call Trace:
 [<c0177d9c>] proc_file_read+0x1b7/0x262
 [<c0149f05>] vfs_read+0x85/0xf3
 [<c0177be5>] proc_file_read+0x0/0x262
 [<c014a26d>] sys_read+0x41/0x6a
 [<c0102be1>] sysenter_past_esp+0x56/0x79
 =======================
Code:  Bad EIP value.
EIP: [<fc281049>] 0xfc281049 SS:ESP 0068:f1e5ff4c

2. After adding ->owner for your favourite /proc file it's still looks racy

	pde = create_proc_entry("foo", 0644, NULL);
	/* so what? pde->owner is NULL here */
	if (pde)
		pde->owner = THIS_MODULE;

3. It's more: setting both ->read_proc and ->data after proc entry creation
   should be oopsable too, if ->read_proc operates on data in a non-trivial
   way (or ->write_proc).

sound/oss/trident.c:
  4446				res = create_proc_entry("ALi5451", 0, NULL);
  4447				if (res) {
  4448					res->write_proc = ali_write_proc;
  					/* ->data is NULL here. */
  4449					res->data = card;
  4450				}

   ali_write_proc() does spin_lock_irqsave on private card lock which is
   believed to be valid.

4. Proposed semantics: PDE should be in maximally working state before
   gluing into main /proc tree (proc_register()).

   	struct proc_entry_raw foo_pe_raw = {
		.owner = THIS_MODULE,
		.name = "foo",
		.mode = 0644,
		.read_proc = foo_read_proc,
		.data = foo_data,
		.parent = foo_parent,
	};

	pde = create_proc_entry(&foo_pe_raw);
	if (!pde)
		return -ENOMEM;

   where "struct proc_entry_raw" is cut down version of "struct proc_dir_entry"
   where new create_proc_entry() would do
   
   	proc_create() or kmalloc()
	fill in fields from passed "struct proc_entry_raw"
	proc_register()

Comments?

Below is 0-order approximation to what I mean (not tested at all):

--- a/fs/afs/proc.c
+++ b/fs/afs/proc.c
@@ -146,17 +146,23 @@ int afs_proc_init(void)
 		goto error;
 	proc_afs->owner = THIS_MODULE;
 
-	p = create_proc_entry("cells", 0, proc_afs);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "cells",
+			.parent = proc_afs,
+			.proc_fops = &afs_proc_cells_fops,
+			.owner = THIS_MODULE,
+		});
 	if (!p)
 		goto error_proc;
-	p->proc_fops = &afs_proc_cells_fops;
-	p->owner = THIS_MODULE;
 
-	p = create_proc_entry("rootcell", 0, proc_afs);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "rootcell",
+			.parent = proc_afs,
+			.proc_fops = &afs_proc_rootcell_fops,
+			.owner = THIS_MODULE,
+		});
 	if (!p)
 		goto error_cells;
-	p->proc_fops = &afs_proc_rootcell_fops;
-	p->owner = THIS_MODULE;
 
 	_leave(" = 0");
 	return 0;
@@ -429,26 +435,35 @@ int afs_proc_cell_setup(struct afs_cell 
 	if (!cell->proc_dir)
 		return -ENOMEM;
 
-	p = create_proc_entry("servers", 0, cell->proc_dir);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "servers",
+			.parent = cell->proc_dir,
+			.proc_fops = &afs_proc_cell_servers_fops,
+			.owner = THIS_MODULE,
+			.data = cell,
+		});
 	if (!p)
 		goto error_proc;
-	p->proc_fops = &afs_proc_cell_servers_fops;
-	p->owner = THIS_MODULE;
-	p->data = cell;
 
-	p = create_proc_entry("vlservers", 0, cell->proc_dir);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "vlservers",
+			.parent = cell->proc_dir,
+			.proc_fops = &afs_proc_cell_vlservers_fops,
+			.owner = THIS_MODULE,
+			.data = cell,
+		});
 	if (!p)
 		goto error_servers;
-	p->proc_fops = &afs_proc_cell_vlservers_fops;
-	p->owner = THIS_MODULE;
-	p->data = cell;
 
-	p = create_proc_entry("volumes", 0, cell->proc_dir);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "volumes",
+			.parent = cell->proc_dir,
+			.proc_fops = &afs_proc_cell_volumes_fops,
+			.owner = THIS_MODULE,
+			.data = cell,
+		});
 	if (!p)
 		goto error_vlservers;
-	p->proc_fops = &afs_proc_cell_volumes_fops;
-	p->owner = THIS_MODULE;
-	p->data = cell;
 
 	_leave(" = 0");
 	return 0;
diff --git a/fs/jbd/journal.c b/fs/jbd/journal.c
index 10fff94..faf0470 100644
--- a/fs/jbd/journal.c
+++ b/fs/jbd/journal.c
@@ -1975,12 +1975,12 @@ #define JBD_PROC_NAME "sys/fs/jbd-debug"
 
 static void __init create_jbd_proc_entry(void)
 {
-	proc_jbd_debug = create_proc_entry(JBD_PROC_NAME, 0644, NULL);
-	if (proc_jbd_debug) {
-		/* Why is this so hard? */
-		proc_jbd_debug->read_proc = read_jbd_debug;
-		proc_jbd_debug->write_proc = write_jbd_debug;
-	}
+	__create_proc_entry(&(struct proc_entry_raw){
+			.name = JBD_PROC_NAME,
+			.mode = 0644,
+			.read_proc = read_jbd_debug,
+			.write_proc = write_jbd_debug,
+		});
 }
 
 static void __exit remove_jbd_proc_entry(void)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 44fc32b..32de473 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1986,12 +1986,12 @@ #define JBD_PROC_NAME "sys/fs/jbd2-debug
 
 static void __init create_jbd_proc_entry(void)
 {
-	proc_jbd_debug = create_proc_entry(JBD_PROC_NAME, 0644, NULL);
-	if (proc_jbd_debug) {
-		/* Why is this so hard? */
-		proc_jbd_debug->read_proc = read_jbd_debug;
-		proc_jbd_debug->write_proc = write_jbd_debug;
-	}
+	__create_proc_entry(&(struct proc_entry_raw){
+			.name = JBD_PROC_NAME,
+			.mode = 0644,
+			.read_proc = read_jbd_debug,
+			.write_proc = write_jbd_debug,
+		});
 }
 
 static void __exit jbd2_remove_jbd_proc_entry(void)
diff --git a/fs/jffs/jffs_proc.c b/fs/jffs/jffs_proc.c
index 9bdd99a..ec00942 100644
--- a/fs/jffs/jffs_proc.c
+++ b/fs/jffs/jffs_proc.c
@@ -85,12 +85,12 @@ int jffs_register_jffs_proc_dir(int mtd,
 	if (!part_root)
 		goto out1;
 
-	/* Create entry for 'info' file */
-	part_info = create_proc_entry ("info", 0, part_root);
-	if (!part_info)
+	if (!__create_proc_entry(&(struct proc_entry_raw){
+			.name = "info",
+			.parent = part_root,
+			.read_proc = jffs_proc_info_read,
+			.data = (void *)c,}))
 		goto out2;
-	part_info->read_proc = jffs_proc_info_read;
-	part_info->data = (void *) c;
 
 	/* Create entry for 'layout' file */
 	part_layout = create_proc_entry ("layout", 0, part_root);
diff --git a/fs/nfs/client.c b/fs/nfs/client.c
index 23ab145..44ca278 100644
--- a/fs/nfs/client.c
+++ b/fs/nfs/client.c
@@ -1406,20 +1406,27 @@ int __init nfs_fs_proc_init(void)
 	proc_fs_nfs->owner = THIS_MODULE;
 
 	/* a file of servers with which we're dealing */
-	p = create_proc_entry("servers", S_IFREG|S_IRUGO, proc_fs_nfs);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "servers",
+			.mode = S_IFREG|S_IRUGO,
+			.parent = proc_fs_nfs,
+			.proc_fops = &nfs_server_list_fops,
+			.owner = THIS_MODULE,
+		});
 	if (!p)
 		goto error_1;
 
-	p->proc_fops = &nfs_server_list_fops;
-	p->owner = THIS_MODULE;
-
 	/* a file of volumes that we have mounted */
-	p = create_proc_entry("volumes", S_IFREG|S_IRUGO, proc_fs_nfs);
+	p = __create_proc_entry(&(struct proc_entry_raw){
+			.name = "volumes",
+			.mode = S_IFREG|S_IRUGO,
+			.parent = proc_fs_nfs,
+			.proc_fops = &nfs_volume_list_fops,
+			.owner = THIS_MODULE,
+		});
 	if (!p)
 		goto error_2;
 
-	p->proc_fops = &nfs_volume_list_fops;
-	p->owner = THIS_MODULE;
 	return 0;
 
 error_2:
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index 853cb87..0bce166 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -657,6 +657,47 @@ struct proc_dir_entry *proc_mkdir(const 
 	return proc_mkdir_mode(name, S_IRUGO | S_IXUGO, parent);
 }
 
+struct proc_dir_entry *__create_proc_entry(struct proc_entry_raw *raw)
+{
+	struct proc_dir_entry *ent;
+	mode_t mode = raw->mode;
+	nlink_t nlink;
+
+	if (S_ISDIR(mode)) {
+		if ((mode & S_IALLUGO) == 0)
+			mode |= S_IRUGO | S_IXUGO;
+		nlink = 2;
+	} else {
+		if ((mode & S_IFMT) == 0)
+			mode |= S_IFREG;
+		if ((mode & S_IALLUGO) == 0)
+			mode |= S_IRUGO;
+		nlink = 1;
+	}
+
+	ent = proc_create(&raw->parent, raw->name, mode, nlink);
+	if (ent) {
+		if (S_ISDIR(mode)) {
+			ent->proc_fops = &proc_dir_operations;
+			ent->proc_iops = &proc_dir_inode_operations;
+		}
+
+		ent->size = raw->size;
+		if (raw->proc_fops)
+			ent->proc_fops = raw->proc_fops;
+		ent->data = raw->data;
+		ent->read_proc = raw->read_proc;
+		ent->write_proc = raw->write_proc;
+		ent->owner = raw->owner;
+
+		if (proc_register(raw->parent, ent) < 0) {
+			kfree(ent);
+			ent = NULL;
+		}
+	}
+	return ent;
+}
+
 struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
 					 struct proc_dir_entry *parent)
 {
diff --git a/fs/proc/root.c b/fs/proc/root.c
index 64d242b..f7d3fda 100644
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -166,6 +166,7 @@ struct proc_dir_entry proc_root = {
 EXPORT_SYMBOL(proc_symlink);
 EXPORT_SYMBOL(proc_mkdir);
 EXPORT_SYMBOL(create_proc_entry);
+EXPORT_SYMBOL(__create_proc_entry);
 EXPORT_SYMBOL(remove_proc_entry);
 EXPORT_SYMBOL(proc_root);
 EXPORT_SYMBOL(proc_root_fs);
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index 87dec8f..0523180 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -68,6 +68,18 @@ struct proc_dir_entry {
 	void *set;
 };
 
+struct proc_entry_raw {
+	const char *name;
+	mode_t mode;
+	loff_t size;
+	const struct file_operations *proc_fops;
+	struct module *owner;
+	struct proc_dir_entry *parent;
+	void *data;
+	read_proc_t *read_proc;
+	write_proc_t *write_proc;
+};
+
 struct kcore_list {
 	struct kcore_list *next;
 	unsigned long addr;
@@ -107,6 +119,7 @@ char *task_mem(struct mm_struct *, char 
 
 extern struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
 						struct proc_dir_entry *parent);
+struct proc_dir_entry *__create_proc_entry(struct proc_entry_raw *raw);
 extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);
 
 extern struct vfsmount *proc_mnt;
@@ -214,6 +227,11 @@ static inline void proc_flush_task(struc
 static inline struct proc_dir_entry *create_proc_entry(const char *name,
 	mode_t mode, struct proc_dir_entry *parent) { return NULL; }
 
+static inline struct proc_dir_entry *__create_proc_entry(struct proc_entry_raw *raw)
+{
+	return NULL;
+}
+
 #define remove_proc_entry(name, parent) do {} while (0)
 
 static inline struct proc_dir_entry *proc_symlink(const char *name,
diff --git a/kernel/configs.c b/kernel/configs.c
index 8fa1fb2..1694608 100644
--- a/kernel/configs.c
+++ b/kernel/configs.c
@@ -85,18 +85,16 @@ static const struct file_operations ikco
 
 static int __init ikconfig_init(void)
 {
-	struct proc_dir_entry *entry;
+	struct proc_entry_raw pe_raw = {
+		.name		= "config.gz",
+		.mode		= S_IFREG | S_IRUGO,
+		.parent		= &proc_root,
+		.proc_fops	= &ikconfig_file_ops,
+		.size		= kernel_config_data_size,
+	};
 
 	/* create the current config file */
-	entry = create_proc_entry("config.gz", S_IFREG | S_IRUGO,
-				  &proc_root);
-	if (!entry)
-		return -ENOMEM;
-
-	entry->proc_fops = &ikconfig_file_ops;
-	entry->size = kernel_config_data_size;
-
-	return 0;
+	return __create_proc_entry(&pe_raw) ? 0 : -ENOMEM;
 }
 
 /***************************************************/
diff --git a/kernel/dma.c b/kernel/dma.c
index 937b13c..51726c0 100644
--- a/kernel/dma.c
+++ b/kernel/dma.c
@@ -149,12 +149,11 @@ static const struct file_operations proc
 
 static int __init proc_dma_init(void)
 {
-	struct proc_dir_entry *e;
-
-	e = create_proc_entry("dma", 0, NULL);
-	if (e)
-		e->proc_fops = &proc_dma_operations;
-
+	struct proc_entry_raw pe_raw = {
+		.name	   = "dma",
+		.proc_fops = &proc_dma_operations,
+	};
+	__create_proc_entry(&pe_raw);
 	return 0;
 }
 
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 61f5c71..aecabf5 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -130,17 +130,17 @@ void register_irq_proc(unsigned int irq)
 
 #ifdef CONFIG_SMP
 	{
-		struct proc_dir_entry *entry;
+		struct proc_entry_raw pe_raw = {
+			.name = "smp_affinity",
+			.mode = 0600,
+			.parent = irq_desc[irq].dir,
+			.data = (void *)(long)irq,
+			.read_proc = irq_affinity_read_proc,
+			.write_proc = irq_affinity_write_proc,
+		};
 
 		/* create /proc/irq/<irq>/smp_affinity */
-		entry = create_proc_entry("smp_affinity", 0600, irq_desc[irq].dir);
-
-		if (entry) {
-			entry->nlink = 1;
-			entry->data = (void *)(long)irq;
-			entry->read_proc = irq_affinity_read_proc;
-			entry->write_proc = irq_affinity_write_proc;
-		}
+		__create_proc_entry(&pe_raw);
 	}
 #endif
 }
diff --git a/kernel/kallsyms.c b/kernel/kallsyms.c
index 6f294ff..3f26794 100644
--- a/kernel/kallsyms.c
+++ b/kernel/kallsyms.c
@@ -442,11 +442,12 @@ static const struct file_operations kall
 
 static int __init kallsyms_init(void)
 {
-	struct proc_dir_entry *entry;
-
-	entry = create_proc_entry("kallsyms", 0444, NULL);
-	if (entry)
-		entry->proc_fops = &kallsyms_operations;
+	struct proc_entry_raw pe_raw = {
+		.name	   = "kallsyms",
+		.mode	   = 0444,
+		.proc_fops = &kallsyms_operations,
+	};
+	__create_proc_entry(&pe_raw);
 	return 0;
 }
 __initcall(kallsyms_init);
diff --git a/kernel/lockdep_proc.c b/kernel/lockdep_proc.c
index b554b40..3d297d4 100644
--- a/kernel/lockdep_proc.c
+++ b/kernel/lockdep_proc.c
@@ -328,16 +328,19 @@ static const struct file_operations proc
 
 static int __init lockdep_proc_init(void)
 {
-	struct proc_dir_entry *entry;
-
-	entry = create_proc_entry("lockdep", S_IRUSR, NULL);
-	if (entry)
-		entry->proc_fops = &proc_lockdep_operations;
-
-	entry = create_proc_entry("lockdep_stats", S_IRUSR, NULL);
-	if (entry)
-		entry->proc_fops = &proc_lockdep_stats_operations;
-
+	struct proc_entry_raw pe_raw_lockdep = {
+		.name = "lockdep",
+		.mode = S_IRUSR,
+		.proc_fops = &proc_lockdep_operations,
+	};
+	struct proc_entry_raw pe_raw_lockdep_stats = {
+		.name = "lockdep_stats",
+		.mode = S_IRUSR,
+		.proc_fops = &proc_lockdep_stats_operations,
+	};
+
+	__create_proc_entry(&pe_raw_lockdep);
+	__create_proc_entry(&pe_raw_lockdep_stats);
 	return 0;
 }
 
diff --git a/kernel/profile.c b/kernel/profile.c
index fb5e03d..19b73a0 100644
--- a/kernel/profile.c
+++ b/kernel/profile.c
@@ -429,15 +429,16 @@ static int prof_cpu_mask_write_proc (str
 
 void create_prof_cpu_mask(struct proc_dir_entry *root_irq_dir)
 {
-	struct proc_dir_entry *entry;
-
+	struct proc_entry_raw pe_raw = {
+		.name = "prof_cpu_mask",
+		.mode = 0600,
+		.parent = root_irq_dir,
+		.data = &prof_cpu_mask,
+		.read_proc = prof_cpu_mask_read_proc,
+		.write_proc = prof_cpu_mask_write_proc,
+	};
 	/* create /proc/irq/prof_cpu_mask */
-	if (!(entry = create_proc_entry("prof_cpu_mask", 0600, root_irq_dir)))
-		return;
-	entry->nlink = 1;
-	entry->data = (void *)&prof_cpu_mask;
-	entry->read_proc = prof_cpu_mask_read_proc;
-	entry->write_proc = prof_cpu_mask_write_proc;
+	__create_proc_entry(&pe_raw);
 }
 
 /*
@@ -561,16 +562,19 @@ #endif
 
 static int __init create_proc_profile(void)
 {
-	struct proc_dir_entry *entry;
+	struct proc_entry_raw pe_raw = {
+		.name	   = "profile",
+		.mode	   = S_IWUSR | S_IRUGO,
+		.proc_fops = &proc_profile_operations,
+		.size	   = (1 + prof_len) * sizeof(atomic_t),
+	};
 
 	if (!prof_on)
 		return 0;
 	if (create_hash_tables())
 		return -1;
-	if (!(entry = create_proc_entry("profile", S_IWUSR | S_IRUGO, NULL)))
+	if (!__create_proc_entry(&pe_raw))
 		return 0;
-	entry->proc_fops = &proc_profile_operations;
-	entry->size = (1+prof_len) * sizeof(atomic_t);
 	hotcpu_notifier(profile_cpu_callback, 0);
 	return 0;
 }
diff --git a/kernel/resource.c b/kernel/resource.c
index 7b9a497..7caf831 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -131,14 +131,17 @@ static const struct file_operations proc
 
 static int __init ioresources_init(void)
 {
-	struct proc_dir_entry *entry;
-
-	entry = create_proc_entry("ioports", 0, NULL);
-	if (entry)
-		entry->proc_fops = &proc_ioports_operations;
-	entry = create_proc_entry("iomem", 0, NULL);
-	if (entry)
-		entry->proc_fops = &proc_iomem_operations;
+	struct proc_entry_raw pe_raw_ioports = {
+		.name = "ioports",
+		.proc_fops = &proc_ioports_operations,
+	};
+	struct proc_entry_raw pe_raw_iomem = {
+		.name = "iomem",
+		.proc_fops = &proc_iomem_operations,
+	};
+
+	__create_proc_entry(&pe_raw_ioports);
+	__create_proc_entry(&pe_raw_iomem);
 	return 0;
 }
 __initcall(ioresources_init);

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