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 <p.bansal@xxxxxxxxxxx>
> 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 <p.bansal@xxxxxxxxxxx>
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
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