[PATCH] jfs: Fix inconsistency between memory allocation and ea_buf->max_size

[Paolo Pisati]

From: Shankara Pailoor <shankarapailoor at gmail.com>

CVE-2018-12233

The code is assuming the buffer is max_size length, but we weren't
allocating enough space for it.

Signed-off-by: Shankara Pailoor <shankarapailoor at gmail.com>
Signed-off-by: Dave Kleikamp <dave.kleikamp at oracle.com>
(cherry picked from commit 92d34134193e5b129dc24f8d79cb9196626e8d7a)
Signed-off-by: Paolo Pisati <paolo.pisati at canonical.com>
---
 fs/jfs/xattr.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/fs/jfs/xattr.c b/fs/jfs/xattr.c
index 6910662..54da0d6 100644
--- a/fs/jfs/xattr.c
+++ b/fs/jfs/xattr.c
@@ -493,15 +493,17 @@ static int ea_get(struct inode *inode, struct ea_buffer *ea_buf, int min_size)
 	if (size > PSIZE) {
 		/*
 		 * To keep the rest of the code simple.  Allocate a
-		 * contiguous buffer to work with
+		 * contiguous buffer to work with. Make the buffer large
+		 * enough to make use of the whole extent.
 		 */
-		ea_buf->xattr = kmalloc(size, GFP_KERNEL);
+		ea_buf->max_size = (size + sb->s_blocksize - 1) &
+		    ~(sb->s_blocksize - 1);
+
+		ea_buf->xattr = kmalloc(ea_buf->max_size, GFP_KERNEL);
 		if (ea_buf->xattr == NULL)
 			return -ENOMEM;
 
 		ea_buf->flag = EA_MALLOC;
-		ea_buf->max_size = (size + sb->s_blocksize - 1) &
-		    ~(sb->s_blocksize - 1);
 
 		if (ea_size == 0)
 			return 0;
-- 
2.7.4