ext4: add corruption check in ext4_xattr_set_entry()

commit 5369a762c882c0b6e9599e4ebbb3a9ba9eee7e2d upstream.

In theory this should have been caught earlier when the xattr list was
verified, but in case it got missed, it's simple enough to add check
to make sure we don't overrun the xattr buffer.

This addresses CVE-2018-10879.

https://bugzilla.kernel.org/show_bug.cgi?id=200001

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c
index ed1cf24a78319fd00cbb364b4d283c3bea5fd5f5..e5abf939989a84da86bb737e49b84f754c1a6fa5 100644 (file)
--- a/fs/ext4/xattr.c
+++ b/fs/ext4/xattr.c
@@ -1559,7 +1559,7 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
                                handle_t *handle, struct inode *inode,
                                bool is_block)
 {
-       struct ext4_xattr_entry *last;
+       struct ext4_xattr_entry *last, *next;
        struct ext4_xattr_entry *here = s->here;
        size_t min_offs = s->end - s->base, name_len = strlen(i->name);
        int in_inode = i->in_inode;
@@ -1594,7 +1594,13 @@ static int ext4_xattr_set_entry(struct ext4_xattr_info *i,
 
        /* Compute min_offs and last. */
        last = s->first;
-       for (; !IS_LAST_ENTRY(last); last = EXT4_XATTR_NEXT(last)) {
+       for (; !IS_LAST_ENTRY(last); last = next) {
+               next = EXT4_XATTR_NEXT(last);
+               if ((void *)next >= s->end) {
+                       EXT4_ERROR_INODE(inode, "corrupted xattr entries");
+                       ret = -EFSCORRUPTED;
+                       goto out;
+               }
                if (!last->e_value_inum && last->e_value_size) {
                        size_t offs = le16_to_cpu(last->e_value_offs);
                        if (offs < min_offs)