4.4-stable review patch. If anyone has any objections, please let me know.
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From: Theodore Ts'o tytso@mit.edu
commit b2569260d55228b617bd82aba6d0db2faeeb4116 upstream.
If ext4 tries to start a reserved handle via jbd2_journal_start_reserved(), and the journal has been aborted, this can result in a NULL pointer dereference. This is because the fields h_journal and h_transaction in the handle structure share the same memory, via a union, so jbd2_journal_start_reserved() will clear h_journal before calling start_this_handle(). If this function fails due to an aborted handle, h_journal will still be NULL, and the call to jbd2_journal_free_reserved() will pass a NULL journal to sub_reserve_credits().
This can be reproduced by running "kvm-xfstests -c dioread_nolock generic/475".
Cc: stable@kernel.org # 3.11 Fixes: 8f7d89f36829b ("jbd2: transaction reservation support") Signed-off-by: Theodore Ts'o tytso@mit.edu Reviewed-by: Andreas Dilger adilger@dilger.ca Reviewed-by: Jan Kara jack@suse.cz Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/jbd2/transaction.c | 1 + 1 file changed, 1 insertion(+)
--- a/fs/jbd2/transaction.c +++ b/fs/jbd2/transaction.c @@ -527,6 +527,7 @@ int jbd2_journal_start_reserved(handle_t */ ret = start_this_handle(journal, handle, GFP_NOFS); if (ret < 0) { + handle->h_journal = journal; jbd2_journal_free_reserved(handle); return ret; }