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    Subject[PATCH 4.14 21/53] ext4: verify the depth of extent tree in ext4_find_extent()
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Theodore Ts'o <tytso@mit.edu>

    commit bc890a60247171294acc0bd67d211fa4b88d40ba upstream.

    If there is a corupted file system where the claimed depth of the
    extent tree is -1, this can cause a massive buffer overrun leading to
    sadness.

    This addresses CVE-2018-10877.

    https://bugzilla.kernel.org/show_bug.cgi?id=199417

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

    ---
    fs/ext4/ext4_extents.h | 1 +
    fs/ext4/extents.c | 6 ++++++
    2 files changed, 7 insertions(+)

    --- a/fs/ext4/ext4_extents.h
    +++ b/fs/ext4/ext4_extents.h
    @@ -103,6 +103,7 @@ struct ext4_extent_header {
    };

    #define EXT4_EXT_MAGIC cpu_to_le16(0xf30a)
    +#define EXT4_MAX_EXTENT_DEPTH 5

    #define EXT4_EXTENT_TAIL_OFFSET(hdr) \
    (sizeof(struct ext4_extent_header) + \
    --- a/fs/ext4/extents.c
    +++ b/fs/ext4/extents.c
    @@ -881,6 +881,12 @@ ext4_find_extent(struct inode *inode, ex

    eh = ext_inode_hdr(inode);
    depth = ext_depth(inode);
    + if (depth < 0 || depth > EXT4_MAX_EXTENT_DEPTH) {
    + EXT4_ERROR_INODE(inode, "inode has invalid extent depth: %d",
    + depth);
    + ret = -EFSCORRUPTED;
    + goto err;
    + }

    if (path) {
    ext4_ext_drop_refs(path);

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