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    Subject[PATCH] UBIFS: fix zero-length truncations
    Date
    From: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

    Always allow truncations to zero, even if budgeting thinks there
    is no space. UBIFS reserves some space for deletions anyway.

    Otherwise, the following happans:
    1. create a file, and write as much as possible there, until ENOSPC
    2. truncate the file, which fails with ENOSPC, which is not good.

    Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
    ---
    fs/ubifs/dir.c | 1 -
    fs/ubifs/file.c | 20 ++++++++++++++++----
    2 files changed, 16 insertions(+), 5 deletions(-)

    diff --git a/fs/ubifs/dir.c b/fs/ubifs/dir.c
    index 5c96f1f..2b267c9 100644
    --- a/fs/ubifs/dir.c
    +++ b/fs/ubifs/dir.c
    @@ -587,7 +587,6 @@ static int ubifs_unlink(struct inode *dir, struct dentry *dentry)
    if (err) {
    if (err != -ENOSPC)
    return err;
    - err = 0;
    budgeted = 0;
    }

    diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c
    index 4071d1c..3d698e2 100644
    --- a/fs/ubifs/file.c
    +++ b/fs/ubifs/file.c
    @@ -793,7 +793,7 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
    int err;
    struct ubifs_budget_req req;
    loff_t old_size = inode->i_size, new_size = attr->ia_size;
    - int offset = new_size & (UBIFS_BLOCK_SIZE - 1);
    + int offset = new_size & (UBIFS_BLOCK_SIZE - 1), budgeted = 1;
    struct ubifs_inode *ui = ubifs_inode(inode);

    dbg_gen("ino %lu, size %lld -> %lld", inode->i_ino, old_size, new_size);
    @@ -811,8 +811,15 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
    /* A funny way to budget for truncation node */
    req.dirtied_ino_d = UBIFS_TRUN_NODE_SZ;
    err = ubifs_budget_space(c, &req);
    - if (err)
    - return err;
    + if (err) {
    + /*
    + * Treat truncations to zero as deletion and always allow them,
    + * just like we do for '->unlink()'.
    + */
    + if (new_size || err != -ENOSPC)
    + return err;
    + budgeted = 0;
    + }

    err = vmtruncate(inode, new_size);
    if (err)
    @@ -869,7 +876,12 @@ static int do_truncation(struct ubifs_info *c, struct inode *inode,
    err = ubifs_jnl_truncate(c, inode, old_size, new_size);
    mutex_unlock(&ui->ui_mutex);
    out_budg:
    - ubifs_release_budget(c, &req);
    + if (budgeted)
    + ubifs_release_budget(c, &req);
    + else {
    + c->nospace = c->nospace_rp = 0;
    + smp_wmb();
    + }
    return err;
    }

    --
    1.5.4.1


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