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    Subject[PATCH 3.10 069/123] ext4: fix reservation overflow in ext4_da_write_begin
    Date
    3.10-stable review patch.  If anyone has any objections, please let me know.

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

    From: Eric Sandeen <sandeen@redhat.com>

    commit 0ff8947fc5f700172b37cbca811a38eb9cb81e08 upstream.

    Delalloc write journal reservations only reserve 1 credit,
    to update the inode if necessary. However, it may happen
    once in a filesystem's lifetime that a file will cross
    the 2G threshold, and require the LARGE_FILE feature to
    be set in the superblock as well, if it was not set already.

    This overruns the transaction reservation, and can be
    demonstrated simply on any ext4 filesystem without the LARGE_FILE
    feature already set:

    dd if=/dev/zero of=testfile bs=1 seek=2147483646 count=1 \
    conv=notrunc of=testfile
    sync
    dd if=/dev/zero of=testfile bs=1 seek=2147483647 count=1 \
    conv=notrunc of=testfile

    leads to:

    EXT4-fs: ext4_do_update_inode:4296: aborting transaction: error 28 in __ext4_handle_dirty_super
    EXT4-fs error (device loop0) in ext4_do_update_inode:4301: error 28
    EXT4-fs error (device loop0) in ext4_reserve_inode_write:4757: Readonly filesystem
    EXT4-fs error (device loop0) in ext4_dirty_inode:4876: error 28
    EXT4-fs error (device loop0) in ext4_da_write_end:2685: error 28

    Adjust the number of credits based on whether the flag is
    already set, and whether the current write may extend past the
    LARGE_FILE limit.

    Signed-off-by: Eric Sandeen <sandeen@redhat.com>
    Signed-off-by: Theodore Ts'o <tytso@mit.edu>
    Reviewed-by: Andreas Dilger <adilger@dilger.ca>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    fs/ext4/inode.c | 17 ++++++++++++++++-
    1 file changed, 16 insertions(+), 1 deletion(-)

    --- a/fs/ext4/inode.c
    +++ b/fs/ext4/inode.c
    @@ -2647,6 +2647,20 @@ static int ext4_nonda_switch(struct supe
    return 0;
    }

    +/* We always reserve for an inode update; the superblock could be there too */
    +static int ext4_da_write_credits(struct inode *inode, loff_t pos, unsigned len)
    +{
    + if (likely(EXT4_HAS_RO_COMPAT_FEATURE(inode->i_sb,
    + EXT4_FEATURE_RO_COMPAT_LARGE_FILE)))
    + return 1;
    +
    + if (pos + len <= 0x7fffffffULL)
    + return 1;
    +
    + /* We might need to update the superblock to set LARGE_FILE */
    + return 2;
    +}
    +
    static int ext4_da_write_begin(struct file *file, struct address_space *mapping,
    loff_t pos, unsigned len, unsigned flags,
    struct page **pagep, void **fsdata)
    @@ -2697,7 +2711,8 @@ retry_grab:
    * of file which has an already mapped buffer.
    */
    retry_journal:
    - handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE, 1);
    + handle = ext4_journal_start(inode, EXT4_HT_WRITE_PAGE,
    + ext4_da_write_credits(inode, pos, len));
    if (IS_ERR(handle)) {
    page_cache_release(page);
    return PTR_ERR(handle);



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