[patch 66/85] eCryptfs: check readlink result was not an errorbefore using it

[Greg KH]

2.6.27-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Duane Griffin <duaneg@xxxxxxxxx>

commit a17d5232de7b53d34229de79ec22f4bb04adb7e4 upstream.

The result from readlink is being used to index into the link name
buffer without checking whether it is a valid length. If readlink
returns an error this will fault or cause memory corruption.

Cc: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxx>
Cc: Dustin Kirkland <kirkland@xxxxxxxxxxxxx>
Cc: ecryptfs-devel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Duane Griffin <duaneg@xxxxxxxxx>
Acked-by: Michael Halcrow <mhalcrow@xxxxxxxxxx>
Acked-by: Tyler Hicks <tyhicks@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 fs/ecryptfs/inode.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -673,10 +673,11 @@ static void *ecryptfs_follow_link(struct
 	ecryptfs_printk(KERN_DEBUG, "Calling readlink w/ "
 			"dentry->d_name.name = [%s]\n", dentry->d_name.name);
 	rc = dentry->d_inode->i_op->readlink(dentry, (char __user *)buf, len);
-	buf[rc] = '\0';
 	set_fs(old_fs);
 	if (rc < 0)
 		goto out_free;
+	else
+		buf[rc] = '\0';
 	rc = 0;
 	nd_set_link(nd, buf);
 	goto out;

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