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ecryptfs: use vfs_get_link() 

Here again we are copying form one buffer to another, while jumping through
hoops to make kernel memory look like userspace memory.

For no good reason, since vfs_get_link() provides exactly what is needed.

As a bonus, now the security hook for readlink is also called on the
underlying inode.

Note: this can be called from link-following context.  But this is okay:

 - not in RCU mode

 - commit e54ad7f1ee ("proc: prevent stacking filesystems on top")

 - ecryptfs is *reading* the underlying symlink not following it, so the
   right security hook is being called

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Cc: Tyler Hicks <tyhicks@canonical.com>
This commit is contained in:
Miklos Szeredi 2016-12-09 16:45:03 +01:00
parent 3f9ca75516
commit 6c988f5759
1 changed files with 12 additions and 17 deletions
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29
fs/ecryptfs/inode.c
View File

@ -631,28 +631,23 @@ out_lock:
static char *ecryptfs_readlink_lower(struct dentry *dentry, size_t *bufsiz) static char *ecryptfs_readlink_lower(struct dentry *dentry, size_t *bufsiz)
{ {
DEFINE_DELAYED_CALL(done);
struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry); struct dentry *lower_dentry = ecryptfs_dentry_to_lower(dentry);
char *lower_buf; const char *link;
char *buf; char *buf;
mm_segment_t old_fs;
int rc; int rc;
lower_buf = kmalloc(PATH_MAX, GFP_KERNEL); link = vfs_get_link(lower_dentry, &done);
if (!lower_buf) if (IS_ERR(link))
return ERR_PTR(-ENOMEM); return ERR_CAST(link);
old_fs = get_fs();
set_fs(get_ds());
rc = d_inode(lower_dentry)->i_op->readlink(lower_dentry,
(char __user *)lower_buf,
PATH_MAX);
set_fs(old_fs);
if (rc < 0)
goto out;
rc = ecryptfs_decode_and_decrypt_filename(&buf, bufsiz, dentry->d_sb, rc = ecryptfs_decode_and_decrypt_filename(&buf, bufsiz, dentry->d_sb,
lower_buf, rc); link, strlen(link));
out: do_delayed_call(&done);
kfree(lower_buf); if (rc)
return rc ? ERR_PTR(rc) : buf; return ERR_PTR(rc);
return buf;
} }
static const char *ecryptfs_get_link(struct dentry *dentry, static const char *ecryptfs_get_link(struct dentry *dentry,