efi: Make efivarfs entries immutable by default

"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 (except for a whitelist), and make tools that
aren't quite so broad-spectrum unset the immutable flag.

Signed-off-by: Peter Jones <pjones@redhat.com>
Tested-by: Lee, Chun-Yi <jlee@suse.com>
Acked-by: Matthew Garrett <mjg59@coreos.com>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>

9 files changed, 258 insertions, 41 deletions

diff --git a/Documentation/filesystems/efivarfs.txt b/Documentation/filesystems/efivarfs.txt
index c477af086e65..686a64bba775 100644
--- a/Documentation/filesystems/efivarfs.txt
+++ b/Documentation/filesystems/efivarfs.txt
@@ -14,3 +14,10 @@ filesystem.
 efivarfs is typically mounted like this,
 
         mount -t efivarfs none /sys/firmware/efi/efivars
+
+Due to the presence of numerous firmware bugs where removing non-standard
+UEFI variables causes the system firmware to fail to POST, efivarfs
+files that are not well-known standardized variables are created
+as immutable files.  This doesn't prevent removal - "chattr -i" will work -
+but it does prevent this kind of failure from being accomplished
+accidentally.
diff --git a/drivers/firmware/efi/vars.c b/drivers/firmware/efi/vars.c
index 9a53da21e7b6..50f10bad2604 100644
--- a/drivers/firmware/efi/vars.c
+++ b/drivers/firmware/efi/vars.c
@@ -172,10 +172,12 @@ struct variable_validate {
 };
 
 /*
- * This is the list of variables we need to validate.
+ * This is the list of variables we need to validate, as well as the
+ * whitelist for what we think is safe not to default to immutable.
  *
  * If it has a validate() method that's not NULL, it'll go into the
- * validation routine.  If not, it is assumed valid.
+ * validation routine.  If not, it is assumed valid, but still used for
+ * whitelisting.
  *
  * Note that it's sorted by {vendor,name}, but globbed names must come after
  * any other name with the same prefix.
@@ -193,11 +195,37 @@ static const struct variable_validate variable_validate[] = {
         { EFI_GLOBAL_VARIABLE_GUID, "ErrOut", validate_device_path },
         { EFI_GLOBAL_VARIABLE_GUID, "ErrOutDev", validate_device_path },
         { EFI_GLOBAL_VARIABLE_GUID, "Lang", validate_ascii_string },
+        { EFI_GLOBAL_VARIABLE_GUID, "OsIndications", NULL },
         { EFI_GLOBAL_VARIABLE_GUID, "PlatformLang", validate_ascii_string },
         { EFI_GLOBAL_VARIABLE_GUID, "Timeout", validate_uint16 },
         { NULL_GUID, "", NULL },
 };
 
+static bool
+variable_matches(const char *var_name, size_t len, const char *match_name,
+                 int *match)
+{
+        for (*match = 0; ; (*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 && *match == len)
+                        return true;
+
+                if (c != u)
+                        return false;
+
+                if (!c)
+                        return true;
+        }
+        return true;
+}
+
 bool
 efivar_validate(efi_guid_t vendor, efi_char16_t *var_name, u8 *data,
                 unsigned long data_size)
@@ -221,35 +249,48 @@ efivar_validate(efi_guid_t vendor, efi_char16_t *var_name, u8 *data,
                 if (efi_guidcmp(vendor, variable_validate[i].vendor))
                         continue;
 
-                for (match = 0; ; match++) {
-                        char c = name[match];
-                        char u = utf8_name[match];
-
-                        /* Wildcard in the matching name means we've matched */
-                        if (c == '*') {
-                                kfree(utf8_name);
-                                return variable_validate[i].validate(var_name,
-                                                        match, data, data_size);
-                        }
-
-                        /* Case sensitive match */
-                        if (c != u)
+                if (variable_matches(utf8_name, utf8_size+1, name, &match)) {
+                        if (variable_validate[i].validate == NULL)
                                 break;
-
-                        /* Reached the end of the string while matching */
-                        if (!c) {
-                                kfree(utf8_name);
-                                return variable_validate[i].validate(var_name,
-                                                        match, data, data_size);
-                        }
+                        kfree(utf8_name);
+                        return variable_validate[i].validate(var_name, match,
+                                                             data, data_size);
                 }
         }
-
         kfree(utf8_name);
         return true;
 }
 EXPORT_SYMBOL_GPL(efivar_validate);
 
+bool
+efivar_variable_is_removable(efi_guid_t vendor, const char *var_name,
+                             size_t len)
+{
+        int i;
+        bool found = false;
+        int match = 0;
+
+        /*
+         * Check if our variable is in the validated variables list
+         */
+        for (i = 0; variable_validate[i].name[0] != '\0'; i++) {
+                if (efi_guidcmp(variable_validate[i].vendor, vendor))
+                        continue;
+
+                if (variable_matches(var_name, len,
+                                     variable_validate[i].name, &match)) {
+                        found = true;
+                        break;
+                }
+        }
+
+        /*
+         * If it's in our list, it is removable.
+         */
+        return found;
+}
+EXPORT_SYMBOL_GPL(efivar_variable_is_removable);
+
 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 c424e4813ec8..d48e0d261d78 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 +104,78 @@ out_free:
         return size;
 }
 
+static int
+efivarfs_ioc_getxflags(struct file *file, void __user *arg)
+{
+        struct inode *inode = file->f_mapping->host;
+        unsigned int i_flags;
+        unsigned int flags = 0;
+
+        i_flags = inode->i_flags;
+        if (i_flags & 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;
+        unsigned int i_flags = 0;
+        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;
+
+        if (flags & FS_IMMUTABLE_FL)
+                i_flags |= S_IMMUTABLE;
+
+
+        error = mnt_want_write_file(file);
+        if (error)
+                return error;
+
+        inode_lock(inode);
+        inode_set_flags(inode, i_flags, S_IMMUTABLE);
+        inode_unlock(inode);
+
+        mnt_drop_write_file(file);
+
+        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 3381b9da9ee6..e2ab6d0497f2 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_removable)
 {
         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_removable ? 0 : S_IMMUTABLE;
                 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_removable = 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 +122,16 @@ 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_removable(var->var.VendorGuid,
+                                         dentry->d_name.name, namelen))
+                is_removable = true;
+
+        inode = efivarfs_get_inode(dir->i_sb, dir, mode, 0, is_removable);
+        if (!inode) {
+                err = -ENOMEM;
+                goto out;
+        }
+
         for (i = 0; i < namelen; i++)
                 var->var.VariableName[i] = dentry->d_name.name[i];
 
@@ -138,7 +145,8 @@ 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 b5ff16addb7c..b4505188e799 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_removable);
 
 extern struct list_head efivarfs_list;
 
diff --git a/fs/efivarfs/super.c b/fs/efivarfs/super.c
index 8651ac28ec0d..dd029d13ea61 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_removable = 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_removable(entry->var.VendorGuid, name, len))
+                is_removable = 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_removable);
         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, true);
         if (!inode)
                 return -ENOMEM;
         inode->i_op = &efivarfs_dir_inode_operations;
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 16ca611aabc8..47be3ad7d3e5 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1201,6 +1201,8 @@ struct efivar_entry *efivar_entry_find(efi_char16_t *name, efi_guid_t guid,
 
 bool efivar_validate(efi_guid_t vendor, efi_char16_t *var_name, u8 *data,
                      unsigned long data_size);
+bool efivar_variable_is_removable(efi_guid_t vendor, const char *name,
+                                  size_t len);
 
 extern struct work_struct efivar_work;
 void efivar_run_worker(void);
diff --git a/tools/testing/selftests/efivarfs/efivarfs.sh b/tools/testing/selftests/efivarfs/efivarfs.sh
index 77edcdcc016b..057278448515 100755
--- a/tools/testing/selftests/efivarfs/efivarfs.sh
+++ b/tools/testing/selftests/efivarfs/efivarfs.sh
@@ -88,7 +88,11 @@ test_delete()
                 exit 1
         fi
 
-        rm $file
+        rm $file 2>/dev/null
+        if [ $? -ne 0 ]; then
+                chattr -i $file
+                rm $file
+        fi
 
         if [ -e $file ]; then
                 echo "$file couldn't be deleted" >&2
@@ -111,6 +115,7 @@ test_zero_size_delete()
                 exit 1
         fi
 
+        chattr -i $file
         printf "$attrs" > $file
 
         if [ -e $file ]; then
@@ -141,7 +146,11 @@ test_valid_filenames()
                         echo "$file could not be created" >&2
                         ret=1
                 else
-                        rm $file
+                        rm $file 2>/dev/null
+                        if [ $? -ne 0 ]; then
+                                chattr -i $file
+                                rm $file
+                        fi
                 fi
         done
 
@@ -174,7 +183,11 @@ test_invalid_filenames()
 
                 if [ -e $file ]; then
                         echo "Creating $file should have failed" >&2
-                        rm $file
+                        rm $file 2>/dev/null
+                        if [ $? -ne 0 ]; then
+                                chattr -i $file
+                                rm $file
+                        fi
                         ret=1
                 fi
         done
diff --git a/tools/testing/selftests/efivarfs/open-unlink.c b/tools/testing/selftests/efivarfs/open-unlink.c
index 8c0764407b3c..4af74f733036 100644
--- a/tools/testing/selftests/efivarfs/open-unlink.c
+++ b/tools/testing/selftests/efivarfs/open-unlink.c
@@ -1,10 +1,68 @@
+#include <errno.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <stdlib.h>
 #include <unistd.h>
+#include <sys/ioctl.h>
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
+#include <linux/fs.h>
+
+static int set_immutable(const char *path, int immutable)
+{
+        unsigned int flags;
+        int fd;
+        int rc;
+        int error;
+
+        fd = open(path, O_RDONLY);
+        if (fd < 0)
+                return fd;
+
+        rc = ioctl(fd, FS_IOC_GETFLAGS, &flags);
+        if (rc < 0) {
+                error = errno;
+                close(fd);
+                errno = error;
+                return rc;
+        }
+
+        if (immutable)
+                flags |= FS_IMMUTABLE_FL;
+        else
+                flags &= ~FS_IMMUTABLE_FL;
+
+        rc = ioctl(fd, FS_IOC_SETFLAGS, &flags);
+        error = errno;
+        close(fd);
+        errno = error;
+        return rc;
+}
+
+static int get_immutable(const char *path)
+{
+        unsigned int flags;
+        int fd;
+        int rc;
+        int error;
+
+        fd = open(path, O_RDONLY);
+        if (fd < 0)
+                return fd;
+
+        rc = ioctl(fd, FS_IOC_GETFLAGS, &flags);
+        if (rc < 0) {
+                error = errno;
+                close(fd);
+                errno = error;
+                return rc;
+        }
+        close(fd);
+        if (flags & FS_IMMUTABLE_FL)
+                return 1;
+        return 0;
+}
 
 int main(int argc, char **argv)
 {
@@ -27,7 +85,7 @@ int main(int argc, char **argv)
         buf[4] = 0;
 
         /* create a test variable */
-        fd = open(path, O_WRONLY | O_CREAT);
+        fd = open(path, O_WRONLY | O_CREAT, 0600);
         if (fd < 0) {
                 perror("open(O_WRONLY)");
                 return EXIT_FAILURE;
@@ -41,6 +99,18 @@ int main(int argc, char **argv)
 
         close(fd);
 
+        rc = get_immutable(path);
+        if (rc < 0) {
+                perror("ioctl(FS_IOC_GETFLAGS)");
+                return EXIT_FAILURE;
+        } else if (rc) {
+                rc = set_immutable(path, 0);
+                if (rc < 0) {
+                        perror("ioctl(FS_IOC_SETFLAGS)");
+                        return EXIT_FAILURE;
+                }
+        }
+
         fd = open(path, O_RDONLY);
         if (fd < 0) {
                 perror("open");