Hi Priya - Thanks for the report and patch. I have some inline comments.
On 2014-09-24 06:58:01, Priya Bansal wrote:
> This patch fixes the issue which was found in
> ecryptfs_setxattr(). Previously, while trying to create a file when ecryptfs
> is mounted over ext4 filesystem with encrypted view enabled, the kernel
> crashes. the reason being the function fsstack_copy_attr_all was trying to
> access dentry->d_inode which was null hence the kernel crashes with NULL
> pointer dereference. Now a check has been applied which prevents such
> condition.
>
> From 74856445756aba18f98aa5b98ad46e7d98f54737 Mon Sep 17 00:00:00 2001
> From: Priya Bansal <[email protected]>
> Date: Fri, 29 Aug 2014 10:27:27 +0530
> Subject: [PATCH] Fix in ecryptfs_setxattr for NULL check before calling
> fsstack_copy_attr_all. This patch fixes the issue which was found in
> ecryptfs_setxattr(). Previously, while trying to create a file when ecryptfs
> is mounted over ext4 filesystem with encrypted view enabled, the kernel
> crashes. the reason being the function fsstack_copy_attr_all was trying to
> access dentry->d_inode which was null hence the kernel crashes with NULL
> pointer dereference. Now a check has been applied which prevents such
> condition.
> Signed-off-by: Priya Bansal <[email protected]>
This commit message is poorly formatted. Have a look at the
"15) The canonical patch format" section of the
Documentation/SubmittingPatches file. It gives a nice description of how
the commit message should be formatted.
> ---
> linux-3.16.1/fs/ecryptfs/inode.c | 18 ++++++++++++++++--
> 1 file changed, 16 insertions(+), 2 deletions(-)
> diff --git a/linux-3.16.1/fs/ecryptfs/inode.c b/linux-3.16.1/fs/ecryptfs/inode.c
> index d4a9431..7da03e5 100644
> --- a/linux-3.16.1/fs/ecryptfs/inode.c
> +++ b/linux-3.16.1/fs/ecryptfs/inode.c
> @@ -1031,6 +1031,8 @@ ecryptfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> {
> int rc = 0;
> struct dentry *lower_dentry;
> + struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
> + &ecryptfs_superblock_to_private(dentry->d_sb)->mount_crypt_stat;
>
> lower_dentry = ecryptfs_dentry_to_lower(dentry);
> if (!lower_dentry->d_inode->i_op->setxattr) {
> @@ -1039,8 +1041,20 @@ ecryptfs_setxattr(struct dentry *dentry, const char *name, const void *value,
> }
>
> rc = vfs_setxattr(lower_dentry, name, value, size, flags);
> - if (!rc)
> - fsstack_copy_attr_all(dentry->d_inode, lower_dentry->d_inode);
> + if (!rc) {
> + if (dentry->d_inode == NULL) {
> + if (mount_crypt_stat->flags
> + & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
> + rc = -EPERM;
> + else if (mount_crypt_stat->flags
> + & ECRYPTFS_XATTR_METADATA_ENABLED)
> + goto out;
> + } else {
> + fsstack_copy_attr_all(dentry->d_inode,
> + lower_dentry->d_inode);
> + }
> + }
> +
> out:
> return rc;
> }
> --
I don't think this is the proper fix. It fixes the NULL pointer
dereference but ecryptfs_setxattr() shouldn't be reachable in encrypted
view mounts. There's a feeble attempt to prevent the modification of
files in ecryptfs_open() when encrypted view is in use but I think we
should force the MS_RDONLY flag on the superblock when the
ecryptfs_encrypted_view mount option is specified.
I'll follow this email up with a patch. I'd appreciate any review and/or
testing you can provide. Thanks!
Tyler
The ecryptfs_encrypted_view mount option greatly changes the
functionality of an eCryptfs mount. Instead of encrypting and decrypting
lower files, it provides a unified view of the encrypted files in the
lower filesystem. The presence of the ecryptfs_encrypted_view mount
option is intended to force a read-only mount and modifying files is not
supported when the feature is in use. See the following commit for more
information:
e77a56d [PATCH] eCryptfs: Encrypted passthrough
This patch forces the mount to be read-only when the
ecryptfs_encrypted_view mount option is specified by setting the
MS_RDONLY flag on the superblock. Additionally, this patch removes some
broken logic in ecryptfs_open() that attempted to prevent modifications
of files when the encrypted view feature was in use. The check in
ecryptfs_open() was not sufficient to prevent file modifications using
system calls that do not operate on a file descriptor.
Signed-off-by: Tyler Hicks <[email protected]>
Reported-by: Priya Bansal <[email protected]>
---
fs/ecryptfs/file.c | 12 ------------
fs/ecryptfs/main.c | 16 +++++++++++++---
2 files changed, 13 insertions(+), 15 deletions(-)
diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index b4b6ab9..e466640 100644
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -190,23 +190,11 @@ static int ecryptfs_open(struct inode *inode, struct file *file)
{
int rc = 0;
struct ecryptfs_crypt_stat *crypt_stat = NULL;
- struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
struct dentry *ecryptfs_dentry = file->f_path.dentry;
/* Private value of ecryptfs_dentry allocated in
* ecryptfs_lookup() */
struct ecryptfs_file_info *file_info;
- mount_crypt_stat = &ecryptfs_superblock_to_private(
- ecryptfs_dentry->d_sb)->mount_crypt_stat;
- if ((mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
- && ((file->f_flags & O_WRONLY) || (file->f_flags & O_RDWR)
- || (file->f_flags & O_CREAT) || (file->f_flags & O_TRUNC)
- || (file->f_flags & O_APPEND))) {
- printk(KERN_WARNING "Mount has encrypted view enabled; "
- "files may only be read\n");
- rc = -EPERM;
- goto out;
- }
/* Released in ecryptfs_release or end of function if failure */
file_info = kmem_cache_zalloc(ecryptfs_file_info_cache, GFP_KERNEL);
ecryptfs_set_file_private(file, file_info);
diff --git a/fs/ecryptfs/main.c b/fs/ecryptfs/main.c
index 1b119d3..34eb843 100644
--- a/fs/ecryptfs/main.c
+++ b/fs/ecryptfs/main.c
@@ -493,6 +493,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
{
struct super_block *s;
struct ecryptfs_sb_info *sbi;
+ struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
struct ecryptfs_dentry_info *root_info;
const char *err = "Getting sb failed";
struct inode *inode;
@@ -511,6 +512,7 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
err = "Error parsing options";
goto out;
}
+ mount_crypt_stat = &sbi->mount_crypt_stat;
s = sget(fs_type, NULL, set_anon_super, flags, NULL);
if (IS_ERR(s)) {
@@ -557,11 +559,19 @@ static struct dentry *ecryptfs_mount(struct file_system_type *fs_type, int flags
/**
* Set the POSIX ACL flag based on whether they're enabled in the lower
- * mount. Force a read-only eCryptfs mount if the lower mount is ro.
- * Allow a ro eCryptfs mount even when the lower mount is rw.
+ * mount.
*/
s->s_flags = flags & ~MS_POSIXACL;
- s->s_flags |= path.dentry->d_sb->s_flags & (MS_RDONLY | MS_POSIXACL);
+ s->s_flags |= path.dentry->d_sb->s_flags & MS_POSIXACL;
+
+ /**
+ * Force a read-only eCryptfs mount when:
+ * 1) The lower mount is ro
+ * 2) The ecryptfs_encrypted_view mount option is specified
+ */
+ if (path.dentry->d_sb->s_flags & MS_RDONLY ||
+ mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
+ s->s_flags |= MS_RDONLY;
s->s_maxbytes = path.dentry->d_sb->s_maxbytes;
s->s_blocksize = path.dentry->d_sb->s_blocksize;
--
2.1.0