From: "Darrick J. Wong" Subject: [PATCH 1/2] ext4: check EA value offset when loading Date: Sun, 14 Sep 2014 10:32:59 -0700 Message-ID: <20140914173259.31996.39833.stgit@birch.djwong.org> References: <20140914173252.31996.86784.stgit@birch.djwong.org> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Cc: linux-ext4@vger.kernel.org To: tytso@mit.edu, darrick.wong@oracle.com Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:34185 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752801AbaINRdF (ORCPT ); Sun, 14 Sep 2014 13:33:05 -0400 In-Reply-To: <20140914173252.31996.86784.stgit@birch.djwong.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: When loading extended attributes, check each entry's value offset to make sure it doesn't collide with the entries. Without this check it is easy to crash the kernel by mounting a malicious FS containing a file with an EA wherein e_value_offs = 0 and e_value_size > 0 and then deleting the EA, which corrupts the name list. (See the f_ea_value_crash test's FS image in e2fsprogs for an example.) Signed-off-by: Darrick J. Wong --- fs/ext4/xattr.c | 34 +++++++++++++++++++++++++--------- 1 file changed, 25 insertions(+), 9 deletions(-) diff --git a/fs/ext4/xattr.c b/fs/ext4/xattr.c index e738733..c11738e 100644 --- a/fs/ext4/xattr.c +++ b/fs/ext4/xattr.c @@ -189,15 +189,29 @@ ext4_listxattr(struct dentry *dentry, char *buffer, size_t size) return ext4_xattr_list(dentry, buffer, size); } -static int -ext4_xattr_check_names(struct ext4_xattr_entry *entry, void *end) +int +ext4_xattr_check_names(struct ext4_xattr_entry *entry, void *end, + void *value_start) { - while (!IS_LAST_ENTRY(entry)) { - struct ext4_xattr_entry *next = EXT4_XATTR_NEXT(entry); + struct ext4_xattr_entry *e = entry; + + while (!IS_LAST_ENTRY(e)) { + struct ext4_xattr_entry *next = EXT4_XATTR_NEXT(e); if ((void *)next >= end) return -EIO; - entry = next; + e = next; } + + while (!IS_LAST_ENTRY(entry)) { + if (entry->e_value_size != 0 && + (value_start + le16_to_cpu(entry->e_value_offs) < + (void *)e + sizeof(__u32) || + value_start + le16_to_cpu(entry->e_value_offs) + + le32_to_cpu(entry->e_value_size) > end)) + return -EIO; + entry = EXT4_XATTR_NEXT(entry); + } + return 0; } @@ -214,7 +228,8 @@ ext4_xattr_check_block(struct inode *inode, struct buffer_head *bh) return -EIO; if (!ext4_xattr_block_csum_verify(inode, bh->b_blocknr, BHDR(bh))) return -EIO; - error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size); + error = ext4_xattr_check_names(BFIRST(bh), bh->b_data + bh->b_size, + bh->b_data); if (!error) set_buffer_verified(bh); return error; @@ -331,7 +346,7 @@ ext4_xattr_ibody_get(struct inode *inode, int name_index, const char *name, header = IHDR(inode, raw_inode); entry = IFIRST(header); end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size; - error = ext4_xattr_check_names(entry, end); + error = ext4_xattr_check_names(entry, end, entry); if (error) goto cleanup; error = ext4_xattr_find_entry(&entry, name_index, name, @@ -463,7 +478,7 @@ ext4_xattr_ibody_list(struct dentry *dentry, char *buffer, size_t buffer_size) raw_inode = ext4_raw_inode(&iloc); header = IHDR(inode, raw_inode); end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size; - error = ext4_xattr_check_names(IFIRST(header), end); + error = ext4_xattr_check_names(IFIRST(header), end, IFIRST(header)); if (error) goto cleanup; error = ext4_xattr_list_entries(dentry, IFIRST(header), @@ -986,7 +1001,8 @@ int ext4_xattr_ibody_find(struct inode *inode, struct ext4_xattr_info *i, is->s.here = is->s.first; is->s.end = (void *)raw_inode + EXT4_SB(inode->i_sb)->s_inode_size; if (ext4_test_inode_state(inode, EXT4_STATE_XATTR)) { - error = ext4_xattr_check_names(IFIRST(header), is->s.end); + error = ext4_xattr_check_names(IFIRST(header), is->s.end, + IFIRST(header)); if (error) return error; /* Find the named attribute. */