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fscrypto: require write access to mount to set encryption policy

Since setting an encryption policy requires writing metadata to the
filesystem, it should be guarded by mnt_want_write/mnt_drop_write.
Otherwise, a user could cause a write to a frozen or readonly
filesystem.  This was handled correctly by f2fs but not by ext4.  Make
fscrypt_process_policy() handle it rather than relying on the filesystem
to get it right.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: stable@vger.kernel.org # 4.1+; check fs/{ext4,f2fs}
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Acked-by: Jaegeuk Kim <jaegeuk@kernel.org>
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ebiggers authored and tytso committed Sep 8, 2016
1 parent 002ced4 commit ba63f23d69a3a10e7e527a02702023da68ef8a6d
Showing with 29 additions and 25 deletions.
  1. +25 −13 fs/crypto/policy.c
  2. +1 −1 fs/ext4/ioctl.c
  3. +1 −8 fs/f2fs/file.c
  4. +2 −3 include/linux/fscrypto.h
View
@@ -11,6 +11,7 @@
#include <linux/random.h>
#include <linux/string.h>
#include <linux/fscrypto.h>
#include <linux/mount.h>
static int inode_has_encryption_context(struct inode *inode)
{
@@ -92,31 +93,42 @@ static int create_encryption_context_from_policy(struct inode *inode,
return inode->i_sb->s_cop->set_context(inode, &ctx, sizeof(ctx), NULL);
}
int fscrypt_process_policy(struct inode *inode,
int fscrypt_process_policy(struct file *filp,
const struct fscrypt_policy *policy)
{
struct inode *inode = file_inode(filp);
int ret;
if (!inode_owner_or_capable(inode))
return -EACCES;
if (policy->version != 0)
return -EINVAL;
ret = mnt_want_write_file(filp);
if (ret)
return ret;
if (!inode_has_encryption_context(inode)) {
if (!S_ISDIR(inode->i_mode))
return -EINVAL;
if (!inode->i_sb->s_cop->empty_dir)
return -EOPNOTSUPP;
if (!inode->i_sb->s_cop->empty_dir(inode))
return -ENOTEMPTY;
return create_encryption_context_from_policy(inode, policy);
ret = -EINVAL;
else if (!inode->i_sb->s_cop->empty_dir)
ret = -EOPNOTSUPP;
else if (!inode->i_sb->s_cop->empty_dir(inode))
ret = -ENOTEMPTY;
else
ret = create_encryption_context_from_policy(inode,
policy);
} else if (!is_encryption_context_consistent_with_policy(inode,
policy)) {
printk(KERN_WARNING
"%s: Policy inconsistent with encryption context\n",
__func__);
ret = -EINVAL;
}
if (is_encryption_context_consistent_with_policy(inode, policy))
return 0;
printk(KERN_WARNING "%s: Policy inconsistent with encryption context\n",
__func__);
return -EINVAL;
mnt_drop_write_file(filp);
return ret;
}
EXPORT_SYMBOL(fscrypt_process_policy);
View
@@ -776,7 +776,7 @@ long ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
(struct fscrypt_policy __user *)arg,
sizeof(policy)))
return -EFAULT;
return fscrypt_process_policy(inode, &policy);
return fscrypt_process_policy(filp, &policy);
#else
return -EOPNOTSUPP;
#endif
View
@@ -1757,21 +1757,14 @@ static int f2fs_ioc_set_encryption_policy(struct file *filp, unsigned long arg)
{
struct fscrypt_policy policy;
struct inode *inode = file_inode(filp);
int ret;
if (copy_from_user(&policy, (struct fscrypt_policy __user *)arg,
sizeof(policy)))
return -EFAULT;
ret = mnt_want_write_file(filp);
if (ret)
return ret;
f2fs_update_time(F2FS_I_SB(inode), REQ_TIME);
ret = fscrypt_process_policy(inode, &policy);
mnt_drop_write_file(filp);
return ret;
return fscrypt_process_policy(filp, &policy);
}
static int f2fs_ioc_get_encryption_policy(struct file *filp, unsigned long arg)
View
@@ -274,8 +274,7 @@ extern void fscrypt_restore_control_page(struct page *);
extern int fscrypt_zeroout_range(struct inode *, pgoff_t, sector_t,
unsigned int);
/* policy.c */
extern int fscrypt_process_policy(struct inode *,
const struct fscrypt_policy *);
extern int fscrypt_process_policy(struct file *, const struct fscrypt_policy *);
extern int fscrypt_get_policy(struct inode *, struct fscrypt_policy *);
extern int fscrypt_has_permitted_context(struct inode *, struct inode *);
extern int fscrypt_inherit_context(struct inode *, struct inode *,
@@ -345,7 +344,7 @@ static inline int fscrypt_notsupp_zeroout_range(struct inode *i, pgoff_t p,
}
/* policy.c */
static inline int fscrypt_notsupp_process_policy(struct inode *i,
static inline int fscrypt_notsupp_process_policy(struct file *f,
const struct fscrypt_policy *p)
{
return -EOPNOTSUPP;

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