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SubjectRe: [ 130/184] CVE-2012-4508 kernel: ext4: AIO vs fallocate stale
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On Tue, 2013-06-04 at 19:23 +0200, Willy Tarreau wrote:
> 2.6.32-longterm review patch. If anyone has any objections, please let me know.
>
> ------------------
> data exposure
>
> From: Jamie Iles <jamie.iles@oracle.com>
>
> CVE-2012-4508 kernel: ext4: AIO vs fallocate stale data exposure
> [dannf: backported to Debian's 2.6.32]

Well, this has an interesting ancestry. The original upstream commits
were c278531d39f3158bfee93dc67da0b77e09776de2,
60d4616f3dc63371b3dc367e5e88fd4b4f037f65 and (most importantly)
dee1f973ca341c266229faa5a1a5bb268bed3531 by Dmitry Monakhov
<dmonakhov@openvz.org>. They were backported into the RHEL 6 kernel by
Lukas Czerner, according to its changelog. Dann got this version from
Oracle's redpatch repository, where, if I understand rightly, Jamie Iles
attempted to regenerate Lukas's patch(es).

Would any of the above named be prepared to put their Signed-off-by to
this?

Ben.

> Signed-off-by: Willy Tarreau <w@1wt.eu>
> ---
> fs/ext4/extents.c | 67 ++++++++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 66 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index f4b471d..3f022ea 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -62,6 +62,7 @@ ext4_fsblk_t ext_pblock(struct ext4_extent *ex)
> * idx_pblock:
> * combine low and high parts of a leaf physical block number into ext4_fsblk_t
> */
> +#define EXT4_EXT_DATA_VALID 0x8 /* extent contains valid data */
> ext4_fsblk_t idx_pblock(struct ext4_extent_idx *ix)
> {
> ext4_fsblk_t block;
> @@ -2933,6 +2934,30 @@ static int ext4_split_unwritten_extents(handle_t *handle,
> ext4_ext_mark_uninitialized(ex3);
> err = ext4_ext_insert_extent(handle, inode, path, ex3, flags);
> if (err == -ENOSPC && may_zeroout) {
> + /*
> + * This is different from the upstream, because we
> + * need only a flag to say that the extent contains
> + * the actual data.
> + *
> + * If the extent contains valid data, which can only
> + * happen if AIO races with fallocate, then we got
> + * here from ext4_convert_unwritten_extents_dio().
> + * So we have to be careful not to zeroout valid data
> + * in the extent.
> + *
> + * To avoid it, we only zeroout the ex3 and extend the
> + * extent which is going to become initialized to cover
> + * ex3 as well. and continue as we would if only
> + * split in two was required.
> + */
> + if (flags & EXT4_EXT_DATA_VALID) {
> + err = ext4_ext_zeroout(inode, ex3);
> + if (err)
> + goto fix_extent_len;
> + max_blocks = allocated;
> + ex2->ee_len = cpu_to_le16(max_blocks);
> + goto skip;
> + }
> err = ext4_ext_zeroout(inode, &orig_ex);
> if (err)
> goto fix_extent_len;
> @@ -2978,6 +3003,7 @@ static int ext4_split_unwritten_extents(handle_t *handle,
>
> allocated = max_blocks;
> }
> +skip:
> /*
> * If there was a change of depth as part of the
> * insertion of ex3 above, we need to update the length
> @@ -3030,11 +3056,16 @@ fix_extent_len:
> ext4_ext_dirty(handle, inode, path + depth);
> return err;
> }
> +
> static int ext4_convert_unwritten_extents_dio(handle_t *handle,
> struct inode *inode,
> + ext4_lblk_t iblock,
> + unsigned int max_blocks,
> struct ext4_ext_path *path)
> {
> struct ext4_extent *ex;
> + ext4_lblk_t ee_block;
> + unsigned int ee_len;
> struct ext4_extent_header *eh;
> int depth;
> int err = 0;
> @@ -3043,6 +3074,30 @@ static int ext4_convert_unwritten_extents_dio(handle_t *handle,
> depth = ext_depth(inode);
> eh = path[depth].p_hdr;
> ex = path[depth].p_ext;
> + ee_block = le32_to_cpu(ex->ee_block);
> + ee_len = ext4_ext_get_actual_len(ex);
> +
> + ext_debug("ext4_convert_unwritten_extents_endio: inode %lu, logical"
> + "block %llu, max_blocks %u\n", inode->i_ino,
> + (unsigned long long)ee_block, ee_len);
> +
> + /* If extent is larger than requested then split is required */
> +
> + if (ee_block != iblock || ee_len > max_blocks) {
> + err = ext4_split_unwritten_extents(handle, inode, path,
> + iblock, max_blocks,
> + EXT4_EXT_DATA_VALID);
> + if (err < 0)
> + goto out;
> + ext4_ext_drop_refs(path);
> + path = ext4_ext_find_extent(inode, iblock, path);
> + if (IS_ERR(path)) {
> + err = PTR_ERR(path);
> + goto out;
> + }
> + depth = ext_depth(inode);
> + ex = path[depth].p_ext;
> + }
>
> err = ext4_ext_get_access(handle, inode, path + depth);
> if (err)
> @@ -3129,7 +3184,8 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
> /* async DIO end_io complete, convert the filled extent to written */
> if (flags == EXT4_GET_BLOCKS_DIO_CONVERT_EXT) {
> ret = ext4_convert_unwritten_extents_dio(handle, inode,
> - path);
> + iblock, max_blocks,
> + path);
> if (ret >= 0)
> ext4_update_inode_fsync_trans(handle, inode, 1);
> goto out2;
> @@ -3498,6 +3554,12 @@ void ext4_ext_truncate(struct inode *inode)
> int err = 0;
>
> /*
> + * finish any pending end_io work so we won't run the risk of
> + * converting any truncated blocks to initialized later
> + */
> + flush_aio_dio_completed_IO(inode);
> +
> + /*
> * probably first extent we're gonna free will be last in block
> */
> err = ext4_writepage_trans_blocks(inode);
> @@ -3630,6 +3692,9 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
> mutex_unlock(&inode->i_mutex);
> return ret;
> }
> +
> + /* Prevent race condition between unwritten */
> + flush_aio_dio_completed_IO(inode);
> retry:
> while (ret >= 0 && ret < max_blocks) {
> block = block + ret;

--
Ben Hutchings
Theory and practice are closer in theory than in practice.
- John Levine, moderator of comp.compilers
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