Preventing "rm -rf /sys/firmware/efi/efivars/" from damage

Preventing "rm -rf /sys/firmware/efi/efivars/" from damage

[Peter Jones]

Hi everybody,
Here's a patchset to make all the variables in efivarfs that aren't well
known to be reasonably safe to delete be immutable by default.

This should alleviate the danger of somebody accidentally using "rm" to
remove some proprietary file that turns out to be important to the
platform, which for some reason it also can't regenerate during POST.

In all cases this is just preventing the user from accidentally
triggering a major security problem with their underlying firmware, but
stopping accidents isn't a bad thing.  These firmwares still need CVEs
and updates to fix them.  Maybe using ESRT and fwupd :)

Thanks.

[PATCH 1/5] Add ucs2 -> utf8 helper functions

[Peter Jones]

This adds ucs2_utf8size(), which tells us how big our ucs2 string is in
bytes, and ucs2_as_utf8, which translates from ucs2 to utf8..
---
 include/linux/ucs2_string.h |  4 +++
 lib/ucs2_string.c           | 62 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+)

diff --git a/include/linux/ucs2_string.h b/include/linux/ucs2_string.h
index cbb20af..bb679b4 100644
--- a/include/linux/ucs2_string.h
+++ b/include/linux/ucs2_string.h
@@ -11,4 +11,8 @@ unsigned long ucs2_strlen(const ucs2_char_t *s);
 unsigned long ucs2_strsize(const ucs2_char_t *data, unsigned long maxlength);
 int ucs2_strncmp(const ucs2_char_t *a, const ucs2_char_t *b, size_t len);
 
+unsigned long ucs2_utf8size(const ucs2_char_t *src);
+unsigned long ucs2_as_utf8(u8 *dest, const ucs2_char_t *src,
+			   unsigned long maxlength);
+
 #endif /* _LINUX_UCS2_STRING_H_ */
diff --git a/lib/ucs2_string.c b/lib/ucs2_string.c
index 6f500ef..17dd74e 100644
--- a/lib/ucs2_string.c
+++ b/lib/ucs2_string.c
@@ -49,3 +49,65 @@ ucs2_strncmp(const ucs2_char_t *a, const ucs2_char_t *b, size_t len)
         }
 }
 EXPORT_SYMBOL(ucs2_strncmp);
+
+unsigned long
+ucs2_utf8size(const ucs2_char_t *src)
+{
+	unsigned long i;
+	unsigned long j = 0;
+
+	for (i = 0; i < ucs2_strlen(src); i++) {
+		u16 c = src[i];
+
+		if (c > 0x800)
+			j += 3;
+		else if (c > 0x80)
+			j += 2;
+		else
+			j += 1;
+	}
+
+	return j;
+}
+EXPORT_SYMBOL(ucs2_utf8size);
+
+/*
+ * copy at most maxlength bytes of whole utf8 characters to dest from the
+ * ucs2 string src.
+ *
+ * The return value is the number of characters copied, not including the
+ * final NUL character.
+ */
+unsigned long
+ucs2_as_utf8(u8 *dest, const ucs2_char_t *src, unsigned long maxlength)
+{
+	unsigned int i;
+	unsigned long j = 0;
+	unsigned long limit = ucs2_strnlen(src, maxlength);
+
+	for (i = 0; maxlength && i < limit; i++) {
+		u16 c = src[i];
+
+		if (c > 0x800) {
+			if (maxlength < 3)
+				break;
+			maxlength -= 3;
+			dest[j++] = 0xe0 | (c & 0xf000) >> 12;
+			dest[j++] = 0x80 | (c & 0x0fc0) >> 8;
+			dest[j++] = 0x80 | (c & 0x003f);
+		} else if (c > 0x80) {
+			if (maxlength < 2)
+				break;
+			maxlength -= 2;
+			dest[j++] = 0xc0 | (c & 0xfe0) >> 5;
+			dest[j++] = 0x80 | (c & 0x01f);
+		} else {
+			maxlength -= 1;
+			dest[j++] = c & 0x7f;
+		}
+	}
+	if (maxlength)
+		dest[j] = '\0';
+	return j;
+}
+EXPORT_SYMBOL(ucs2_as_utf8);
-- 
2.5.0

[PATCH 2/5] efi: use ucs2_as_utf8 in efivarfs instead of open coding a bad version

[Peter Jones]

Translate EFI's UCS-2 variable names to UTF-8 instead of just assuming
all variable names fit in ASCII.

Signed-off-by: Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 drivers/firmware/efi/efivars.c | 13 ++++---------
 fs/efivarfs/super.c            |  7 +++----
 2 files changed, 7 insertions(+), 13 deletions(-)

diff --git a/drivers/firmware/efi/efivars.c b/drivers/firmware/efi/efivars.c
index 756eca8..eef6331 100644
--- a/drivers/firmware/efi/efivars.c
+++ b/drivers/firmware/efi/efivars.c
@@ -540,7 +540,7 @@ static ssize_t efivar_delete(struct file *filp, struct kobject *kobj,
 static int
 efivar_create_sysfs_entry(struct efivar_entry *new_var)
 {
-	int i, short_name_size;
+	int short_name_size;
 	char *short_name;
 	unsigned long variable_name_size;
 	efi_char16_t *variable_name;
@@ -553,22 +553,17 @@ efivar_create_sysfs_entry(struct efivar_entry *new_var)
 	 * Length of the variable bytes in ASCII, plus the '-' separator,
 	 * plus the GUID, plus trailing NUL
 	 */
-	short_name_size = variable_name_size / sizeof(efi_char16_t)
-				+ 1 + EFI_VARIABLE_GUID_LEN + 1;
+	short_name_size = ucs2_utf8size(new_var->var.VariableName) + 1;
 
 	short_name = kzalloc(short_name_size, GFP_KERNEL);
 
 	if (!short_name)
 		return -ENOMEM;
 
-	/* Convert Unicode to normal chars (assume top bits are 0),
-	   ala UTF-8 */
-	for (i=0; i < (int)(variable_name_size / sizeof(efi_char16_t)); i++) {
-		short_name[i] = variable_name[i] & 0xFF;
-	}
+	ucs2_as_utf8(short_name, variable_name, short_name_size);
+
 	/* This is ugly, but necessary to separate one vendor's
 	   private variables from another's.         */
-
 	*(short_name + strlen(short_name)) = '-';
 	efi_guid_to_str(&new_var->var.VendorGuid,
 			 short_name + strlen(short_name));
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index b8a564f..8651ac2 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -118,7 +118,7 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	struct dentry *dentry, *root = sb->s_root;
 	unsigned long size = 0;
 	char *name;
-	int len, i;
+	int len;
 	int err = -ENOMEM;
 
 	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
@@ -128,15 +128,14 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	memcpy(entry->var.VariableName, name16, name_size);
 	memcpy(&(entry->var.VendorGuid), &vendor, sizeof(efi_guid_t));
 
-	len = ucs2_strlen(entry->var.VariableName);
+	len = ucs2_utf8size(entry->var.VariableName);
 
 	/* name, plus '-', plus GUID, plus NUL*/
 	name = kmalloc(len + 1 + EFI_VARIABLE_GUID_LEN + 1, GFP_KERNEL);
 	if (!name)
 		goto fail;
 
-	for (i = 0; i < len; i++)
-		name[i] = entry->var.VariableName[i] & 0xFF;
+	ucs2_as_utf8(name, entry->var.VariableName, len);
 
 	name[len] = '-';
 
-- 
2.5.0

[PATCH 3/5] efi: do variable name validation tests in utf8

[Peter Jones]

Actually translate from ucs2 to utf8 before doing the test, and then
test against our other utf8 data, instead of fudging it.

Signed-off-by: Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 drivers/firmware/efi/vars.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 70a0fb1..36c5a6e 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -192,7 +192,15 @@ bool
 efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
 {
 	int i;
-	u16 *unicode_name = var_name;
+	unsigned long utf8_size;
+	u8 *utf8_name;
+
+	utf8_size = ucs2_utf8size(var_name);
+	utf8_name = kmalloc(utf8_size + 1, GFP_KERNEL);
+	if (!utf8_name)
+		return false;
+
+	ucs2_as_utf8(utf8_name, var_name, len);
 
 	for (i = 0; variable_validate[i].validate != NULL; i++) {
 		const char *name = variable_validate[i].name;
@@ -200,28 +208,29 @@ efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
 
 		for (match = 0; ; match++) {
 			char c = name[match];
-			u16 u = unicode_name[match];
-
-			/* All special variables are plain ascii */
-			if (u > 127)
-				return true;
+			char u = utf8_name[match];
 
 			/* Wildcard in the matching name means we've matched */
-			if (c == '*')
+			if (c == '*') {
+				kfree(utf8_name);
 				return variable_validate[i].validate(var_name,
 							     match, data, len);
+			}
 
 			/* Case sensitive match */
 			if (c != u)
 				break;
 
 			/* Reached the end of the string while matching */
-			if (!c)
+			if (!c) {
+				kfree(utf8_name);
 				return variable_validate[i].validate(var_name,
 							     match, data, len);
+			}
 		}
 	}
 
+	kfree(utf8_name);
 	return true;
 }
 EXPORT_SYMBOL_GPL(efivar_validate);
-- 
2.5.0

[PATCH 4/5] efi: make our variable validation list include the guid

[Peter Jones]

We're not actually checking the guid in the validation code, but it
makes it easier to use the list for other things later.

Signed-off-by: Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 drivers/firmware/efi/vars.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 36c5a6e..e084d08 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -165,27 +165,28 @@ validate_ascii_string(efi_char16_t *var_name, int match, u8 *buffer,
 }
 
 struct variable_validate {
+	efi_guid_t guid;
 	char *name;
 	bool (*validate)(efi_char16_t *var_name, int match, u8 *data,
 			 unsigned long len);
 };
 
 static const struct variable_validate variable_validate[] = {
-	{ "BootNext", validate_uint16 },
-	{ "BootOrder", validate_boot_order },
-	{ "DriverOrder", validate_boot_order },
-	{ "Boot*", validate_load_option },
-	{ "Driver*", validate_load_option },
-	{ "ConIn", validate_device_path },
-	{ "ConInDev", validate_device_path },
-	{ "ConOut", validate_device_path },
-	{ "ConOutDev", validate_device_path },
-	{ "ErrOut", validate_device_path },
-	{ "ErrOutDev", validate_device_path },
-	{ "Timeout", validate_uint16 },
-	{ "Lang", validate_ascii_string },
-	{ "PlatformLang", validate_ascii_string },
-	{ "", NULL },
+	{ EFI_GLOBAL_VARIABLE_GUID, "BootNext", validate_uint16 },
+	{ EFI_GLOBAL_VARIABLE_GUID, "BootOrder", validate_boot_order },
+	{ EFI_GLOBAL_VARIABLE_GUID, "DriverOrder", validate_boot_order },
+	{ EFI_GLOBAL_VARIABLE_GUID, "Boot*", validate_load_option },
+	{ EFI_GLOBAL_VARIABLE_GUID, "Driver*", validate_load_option },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ConIn", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ConInDev", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ConOut", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ConOutDev", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ErrOut", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "ErrOutDev", validate_device_path },
+	{ EFI_GLOBAL_VARIABLE_GUID, "Timeout", validate_uint16 },
+	{ EFI_GLOBAL_VARIABLE_GUID, "Lang", validate_ascii_string },
+	{ EFI_GLOBAL_VARIABLE_GUID, "PlatformLang", validate_ascii_string },
+	{ NULL_GUID, "", NULL },
 };
 
 bool
@@ -202,7 +203,7 @@ efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
 
 	ucs2_as_utf8(utf8_name, var_name, len);
 
-	for (i = 0; variable_validate[i].validate != NULL; i++) {
+	for (i = 0; variable_validate[i].name[0] != '\0'; i++) {
 		const char *name = variable_validate[i].name;
 		int match;
 
-- 
2.5.0

[PATCH 5/5] efi: Make efivarfs entries immutable by default.

[Peter Jones]

"rm -rf" is bricking some peoples' laptops because of variables being
used to store non-reinitializable firmware driver data that's required
to POST the hardware.

These are 100% bugs, and they need to be fixed, but in the mean time it
shouldn't be easy to *accidentally* brick machines.

We have to have delete working, and picking which variables do and don't
work for deletion is quite intractable, so instead make everything
immutable by default, and make tools that aren't quite so broad-spectrum
unset the immutable flag.

Signed-off-by: Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
 drivers/firmware/efi/vars.c | 82 +++++++++++++++++++++++++++++++++------------
 fs/efivarfs/file.c          | 69 ++++++++++++++++++++++++++++++++++++++
 fs/efivarfs/inode.c         | 32 ++++++++++++------
 fs/efivarfs/internal.h      |  3 +-
 fs/efivarfs/super.c         |  9 +++--
 include/linux/efi.h         |  2 ++
 6 files changed, 162 insertions(+), 35 deletions(-)

diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index e084d08..3a16a57 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -186,9 +186,32 @@ static const struct variable_validate variable_validate[] = {
 	{ EFI_GLOBAL_VARIABLE_GUID, "Timeout", validate_uint16 },
 	{ EFI_GLOBAL_VARIABLE_GUID, "Lang", validate_ascii_string },
 	{ EFI_GLOBAL_VARIABLE_GUID, "PlatformLang", validate_ascii_string },
+	{ EFI_GLOBAL_VARIABLE_GUID, "OsIndications", NULL },
 	{ NULL_GUID, "", NULL },
 };
 
+static bool
+variable_matches(const char *var_name, size_t len, const char *match_name,
+		 int *match)
+{
+	for (*match = 0; match_name[*match] && *match < len; (*match)++) {
+		char c = match_name[*match];
+		char u = var_name[*match];
+
+		/* Wildcard in the matching name means we've matched */
+		if (c == '*')
+			return true;
+
+		/* Case sensitive match */
+		if (c != u)
+			break;
+
+		if (!c)
+			return true;
+	}
+	return false;
+}
+
 bool
 efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
 {
@@ -205,36 +228,53 @@ efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len)
 
 	for (i = 0; variable_validate[i].name[0] != '\0'; i++) {
 		const char *name = variable_validate[i].name;
-		int match;
+		int match = 0;
 
-		for (match = 0; ; match++) {
-			char c = name[match];
-			char u = utf8_name[match];
+		if (variable_matches(utf8_name, utf8_size+1, name, &match)) {
+			kfree(utf8_name);
+			if (variable_validate[i].validate == NULL)
+				break;
+			return variable_validate[i].validate(var_name, match,
+							     data, len);
+		}
 
-			/* Wildcard in the matching name means we've matched */
-			if (c == '*') {
-				kfree(utf8_name);
-				return variable_validate[i].validate(var_name,
-							     match, data, len);
-			}
+	}
+	kfree(utf8_name);
+	return true;
+}
+EXPORT_SYMBOL_GPL(efivar_validate);
 
-			/* Case sensitive match */
-			if (c != u)
-				break;
+bool
+efivar_variable_is_protected(efi_guid_t vendor, const char *var_name,
+			     size_t len)
+{
+	int i;
+	bool found = false;
+	int match = 0;
 
-			/* Reached the end of the string while matching */
-			if (!c) {
-				kfree(utf8_name);
-				return variable_validate[i].validate(var_name,
-							     match, data, len);
-			}
+	/*
+	 * Now check the validated variables list and then the whitelist -
+	 * both are whitelists
+	 */
+	for (i = 0; variable_validate[i].name[0] != '\0'; i++) {
+		if (efi_guidcmp(variable_validate[i].guid, vendor))
+			continue;
+
+		if (variable_matches(var_name, len,
+				     variable_validate[i].name, &match)) {
+			found = true;
+			break;
 		}
 	}
 
-	kfree(utf8_name);
+	/*
+	 * If we found it in our list, it /isn't/ one of our protected names.
+	 */
+	if (found)
+		return false;
 	return true;
 }
-EXPORT_SYMBOL_GPL(efivar_validate);
+EXPORT_SYMBOL_GPL(efivar_variable_is_protected);
 
 static efi_status_t
 check_var_size(u32 attributes, unsigned long size)
diff --git a/fs/efivarfs/file.c b/fs/efivarfs/file.c
index c424e48..b793c85 100644
--- a/fs/efivarfs/file.c
+++ b/fs/efivarfs/file.c
@@ -10,6 +10,7 @@
 #include <linux/efi.h>
 #include <linux/fs.h>
 #include <linux/slab.h>
+#include <linux/mount.h>
 
 #include "internal.h"
 
@@ -103,9 +104,77 @@ out_free:
 	return size;
 }
 
+static int
+efivarfs_ioc_getxflags(struct file *file,
+		       void __user *arg)
+{
+	struct inode *inode = file->f_mapping->host;
+	unsigned int iflags;
+	unsigned int flags = 0;
+
+	iflags = inode->i_flags;
+	if (iflags & S_IMMUTABLE)
+		flags |= FS_IMMUTABLE_FL;
+
+	if (copy_to_user(arg, &flags, sizeof(flags)))
+		return -EFAULT;
+	return 0;
+}
+
+static int
+efivarfs_ioc_setxflags(struct file *file,
+		       void __user *arg)
+{
+	struct inode *inode = file->f_mapping->host;
+	unsigned int flags;
+	int error;
+
+	if (!inode_owner_or_capable(inode))
+		return -EACCES;
+
+	if (copy_from_user(&flags, arg, sizeof(flags)))
+		return -EFAULT;
+
+	if (flags & ~FS_IMMUTABLE_FL)
+		return -EOPNOTSUPP;
+
+	if (!capable(CAP_LINUX_IMMUTABLE))
+		return -EPERM;
+
+	error = mnt_want_write_file(file);
+	if (error)
+		return error;
+
+	if (flags & FS_IMMUTABLE_FL)
+		inode->i_flags |= S_IMMUTABLE;
+	else
+		inode->i_flags &= ~S_IMMUTABLE;
+
+	return 0;
+}
+
+long
+efivarfs_file_ioctl(
+		    struct file *file,
+		    unsigned int cmd,
+		    unsigned long p)
+{
+	void __user *arg = (void __user *)p;
+
+	switch (cmd) {
+	case FS_IOC_GETFLAGS:
+		return efivarfs_ioc_getxflags(file, arg);
+	case FS_IOC_SETFLAGS:
+		return efivarfs_ioc_setxflags(file, arg);
+	}
+
+	return -ENOTTY;
+}
+
 const struct file_operations efivarfs_file_operations = {
 	.open	= simple_open,
 	.read	= efivarfs_file_read,
 	.write	= efivarfs_file_write,
 	.llseek	= no_llseek,
+	.unlocked_ioctl = efivarfs_file_ioctl,
 };
diff --git a/fs/efivarfs/inode.c b/fs/efivarfs/inode.c
index 3381b9d..00735e0 100644
--- a/fs/efivarfs/inode.c
+++ b/fs/efivarfs/inode.c
@@ -15,7 +15,8 @@
 #include "internal.h"
 
 struct inode *efivarfs_get_inode(struct super_block *sb,
-				const struct inode *dir, int mode, dev_t dev)
+				const struct inode *dir, int mode,
+				dev_t dev, bool is_protected)
 {
 	struct inode *inode = new_inode(sb);
 
@@ -23,6 +24,7 @@ struct inode *efivarfs_get_inode(struct super_block *sb,
 		inode->i_ino = get_next_ino();
 		inode->i_mode = mode;
 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+		inode->i_flags = is_protected ? S_IMMUTABLE : 0;
 		switch (mode & S_IFMT) {
 		case S_IFREG:
 			inode->i_fop = &efivarfs_file_operations;
@@ -102,22 +104,17 @@ static void efivarfs_hex_to_guid(const char *str, efi_guid_t *guid)
 static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 			  umode_t mode, bool excl)
 {
-	struct inode *inode;
+	struct inode *inode = NULL;
 	struct efivar_entry *var;
 	int namelen, i = 0, err = 0;
+	bool is_protected = false;
 
 	if (!efivarfs_valid_name(dentry->d_name.name, dentry->d_name.len))
 		return -EINVAL;
 
-	inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0);
-	if (!inode)
-		return -ENOMEM;
-
 	var = kzalloc(sizeof(struct efivar_entry), GFP_KERNEL);
-	if (!var) {
-		err = -ENOMEM;
-		goto out;
-	}
+	if (!var)
+		return -ENOMEM;
 
 	/* length of the variable name itself: remove GUID and separator */
 	namelen = dentry->d_name.len - EFI_VARIABLE_GUID_LEN - 1;
@@ -125,6 +122,18 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 	efivarfs_hex_to_guid(dentry->d_name.name + namelen + 1,
 			&var->var.VendorGuid);
 
+	if (efivar_variable_is_protected(var->var.VendorGuid,
+					 dentry->d_name.name,
+					 dentry->d_name.len))
+		is_protected = true;
+
+	inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0, is_protected);
+	if (!inode) {
+		err = -ENOMEM;
+		goto out;
+	}
+	inode->i_flags = 0;
+
 	for (i = 0; i < namelen; i++)
 		var->var.VariableName[i] = dentry->d_name.name[i];
 
@@ -138,7 +147,8 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
 out:
 	if (err) {
 		kfree(var);
-		iput(inode);
+		if (inode)
+			iput(inode);
 	}
 	return err;
 }
diff --git a/fs/efivarfs/internal.h b/fs/efivarfs/internal.h
index b5ff16a..f435832 100644
--- a/fs/efivarfs/internal.h
+++ b/fs/efivarfs/internal.h
@@ -15,7 +15,8 @@ extern const struct file_operations efivarfs_file_operations;
 extern const struct inode_operations efivarfs_dir_inode_operations;
 extern bool efivarfs_valid_name(const char *str, int len);
 extern struct inode *efivarfs_get_inode(struct super_block *sb,
-			const struct inode *dir, int mode, dev_t dev);
+			const struct inode *dir, int mode, dev_t dev,
+			bool is_protected);
 
 extern struct list_head efivarfs_list;
 
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 8651ac2..6d5dd56 100644
--- a/fs/efivarfs/super.c
+++ b/fs/efivarfs/super.c
@@ -120,6 +120,7 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 	char *name;
 	int len;
 	int err = -ENOMEM;
+	bool is_protected = false;
 
 	entry = kzalloc(sizeof(*entry), GFP_KERNEL);
 	if (!entry)
@@ -137,13 +138,17 @@ static int efivarfs_callback(efi_char16_t *name16, efi_guid_t vendor,
 
 	ucs2_as_utf8(name, entry->var.VariableName, len);
 
+	if (efivar_variable_is_protected(entry->var.VendorGuid, name, len))
+		is_protected = true;
+
 	name[len] = '-';
 
 	efi_guid_to_str(&entry->var.VendorGuid, name + len + 1);
 
 	name[len + EFI_VARIABLE_GUID_LEN+1] = '\0';
 
-	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0644, 0);
+	inode = efivarfs_get_inode(sb, d_inode(root), S_IFREG | 0644, 0,
+				   is_protected);
 	if (!inode)
 		goto fail_name;
 
@@ -199,7 +204,7 @@ static int efivarfs_fill_super(struct super_block *sb, void *data, int silent)
 	sb->s_d_op		= &efivarfs_d_ops;
 	sb->s_time_gran         = 1;
 
-	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0);
+	inode = efivarfs_get_inode(sb, NULL, S_IFDIR | 0755, 0, false);
 	if (!inode)
 		return -ENOMEM;
 	inode->i_op = &efivarfs_dir_inode_operations;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 569b5a8..afc841b 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1200,6 +1200,8 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
 				       struct list_head *head, bool remove);
 
 bool efivar_validate(efi_char16_t *var_name, u8 *data, unsigned long len);
+bool efivar_variable_is_protected(efi_guid_t vendor, const char *name,
+				  size_t len);
 
 extern struct work_struct efivar_work;
 void efivar_run_worker(void);
-- 
2.5.0

Re: [PATCH 5/5] efi: Make efivarfs entries immutable by default.

[Matt Fleming]

On Tue, 02 Feb, at 05:33:06PM, Peter Jones wrote:
> "rm -rf" is bricking some peoples' laptops because of variables being
> used to store non-reinitializable firmware driver data that's required
> to POST the hardware.
> 
> These are 100% bugs, and they need to be fixed, but in the mean time it
> shouldn't be easy to *accidentally* brick machines.
> 
> We have to have delete working, and picking which variables do and don't
> work for deletion is quite intractable, so instead make everything
> immutable by default, and make tools that aren't quite so broad-spectrum
> unset the immutable flag.
> 
> Signed-off-by: Peter Jones <pjones-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> ---
>  drivers/firmware/efi/vars.c | 82 +++++++++++++++++++++++++++++++++------------
>  fs/efivarfs/file.c          | 69 ++++++++++++++++++++++++++++++++++++++
>  fs/efivarfs/inode.c         | 32 ++++++++++++------
>  fs/efivarfs/internal.h      |  3 +-
>  fs/efivarfs/super.c         |  9 +++--
>  include/linux/efi.h         |  2 ++
>  6 files changed, 162 insertions(+), 35 deletions(-)
 
Only the last two patches (4 and 5) of this series are required to fix
this bricking issue, right? The fix needs backporting to stable
kernels and if the first three patches are just improving the
robustness of UCS-2 handling, they don't qualify for backport.

> diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
> index e084d08..3a16a57 100644
> --- a/drivers/firmware/efi/vars.c
> +++ b/drivers/firmware/efi/vars.c
> @@ -186,9 +186,32 @@ static const struct variable_validate variable_validate[] = {
>  	{ EFI_GLOBAL_VARIABLE_GUID, "Timeout", validate_uint16 },
>  	{ EFI_GLOBAL_VARIABLE_GUID, "Lang", validate_ascii_string },
>  	{ EFI_GLOBAL_VARIABLE_GUID, "PlatformLang", validate_ascii_string },
> +	{ EFI_GLOBAL_VARIABLE_GUID, "OsIndications", NULL },
>  	{ NULL_GUID, "", NULL },
>  };

It would be good to include a comment above this table that documents
what it is used for since we're adding one more use.
  
> +bool
> +efivar_variable_is_protected(efi_guid_t vendor, const char *var_name,
> +			     size_t len)
> +{
> +	int i;
> +	bool found = false;
> +	int match = 0;
>  
> -			/* Reached the end of the string while matching */
> -			if (!c) {
> -				kfree(utf8_name);
> -				return variable_validate[i].validate(var_name,
> -							     match, data, len);
> -			}
> +	/*
> +	 * Now check the validated variables list and then the whitelist -
> +	 * both are whitelists
> +	 */
> +	for (i = 0; variable_validate[i].name[0] != '\0'; i++) {
> +		if (efi_guidcmp(variable_validate[i].guid, vendor))
> +			continue;
> +
> +		if (variable_matches(var_name, len,
> +				     variable_validate[i].name, &match)) {
> +			found = true;
> +			break;
>  		}
>  	}
>  
> -	kfree(utf8_name);
> +	/*
> +	 * If we found it in our list, it /isn't/ one of our protected names.
> +	 */
> +	if (found)
> +		return false;
>  	return true;
>  }
> -EXPORT_SYMBOL_GPL(efivar_validate);
> +EXPORT_SYMBOL_GPL(efivar_variable_is_protected);

"protected" is a bit of a vague word in this context.

How about inverting the return values and naming it,

efivar_variable_is_removable() ? Or efivar_variable_is_deletable() ?
  
> @@ -102,22 +104,17 @@ static void efivarfs_hex_to_guid(const char *str, efi_guid_t *guid)
>  static int efivarfs_create(struct inode *dir, struct dentry *dentry,
>  			  umode_t mode, bool excl)
>  {
> -	struct inode *inode;
> +	struct inode *inode = NULL;
>  	struct efivar_entry *var;
>  	int namelen, i = 0, err = 0;
> +	bool is_protected = false;
>  
>  	if (!efivarfs_valid_name(dentry->d_name.name, dentry->d_name.len))
>  		return -EINVAL;
>  
> -	inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0);
> -	if (!inode)
> -		return -ENOMEM;
> -
>  	var = kzalloc(sizeof(struct efivar_entry), GFP_KERNEL);
> -	if (!var) {
> -		err = -ENOMEM;
> -		goto out;
> -	}
> +	if (!var)
> +		return -ENOMEM;
>  
>  	/* length of the variable name itself: remove GUID and separator */
>  	namelen = dentry->d_name.len - EFI_VARIABLE_GUID_LEN - 1;
> @@ -125,6 +122,18 @@ static int efivarfs_create(struct inode *dir, struct dentry *dentry,
>  	efivarfs_hex_to_guid(dentry->d_name.name + namelen + 1,
>  			&var->var.VendorGuid);
>  
> +	if (efivar_variable_is_protected(var->var.VendorGuid,
> +					 dentry->d_name.name,
> +					 dentry->d_name.len))
> +		is_protected = true;
> +
> +	inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0, is_protected);
> +	if (!inode) {
> +		err = -ENOMEM;
> +		goto out;
> +	}
> +	inode->i_flags = 0;
> +

What's the point looking up efivar_variable_is_protected() if you
trash ->i_flags?

Re: Preventing "rm -rf /sys/firmware/efi/efivars/" from damage

[Matthew Garrett]

For the set:

Acked-by: Matthew Garrett <mjg59-JW9irJGTvgXQT0dZR+AlfA@public.gmane.org>

-- 
Matthew Garrett | mjg59-1xO5oi07KQx4cg9Nei1l7Q@public.gmane.org