jbd2: don't mark block as modified if the handle is out of credits

Do not set the b_modified flag in block's journal head should not
until after we're sure that jbd2_journal_dirty_metadat() will not
abort with an error due to there not being enough space reserved in
the jbd2 handle.

Otherwise, future attempts to modify the buffer may lead a large
number of spurious errors and warnings.

This addresses CVE-2018-10883.

https://bugzilla.kernel.org/show_bug.cgi?id=200071

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

diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 51dd68e67b0f3abfcd115196724079e226467d09..c0b66a7a795b1cd22de3061930e454ff24394925 100644 (file)
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1361,6 +1361,13 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
                if (jh->b_transaction == transaction &&
                    jh->b_jlist != BJ_Metadata) {
                        jbd_lock_bh_state(bh);
+                       if (jh->b_transaction == transaction &&
+                           jh->b_jlist != BJ_Metadata)
+                               pr_err("JBD2: assertion failure: h_type=%u "
+                                      "h_line_no=%u block_no=%llu jlist=%u\n",
+                                      handle->h_type, handle->h_line_no,
+                                      (unsigned long long) bh->b_blocknr,
+                                      jh->b_jlist);
                        J_ASSERT_JH(jh, jh->b_transaction != transaction ||
                                        jh->b_jlist == BJ_Metadata);
                        jbd_unlock_bh_state(bh);
@@ -1380,11 +1387,11 @@ int jbd2_journal_dirty_metadata(handle_t *handle, struct buffer_head *bh)
                 * of the transaction. This needs to be done
                 * once a transaction -bzzz
                 */
-               jh->b_modified = 1;
                if (handle->h_buffer_credits <= 0) {
                        ret = -ENOSPC;
                        goto out_unlock_bh;
                }
+               jh->b_modified = 1;
                handle->h_buffer_credits--;
        }