Commit b2569260 authored Apr 18, 2018 by Theodore Ts'o

ext4: set h_journal if there is a failure starting a reserved handle



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: 8f7d89f3 ("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>

parent 349fa7d6

fs/jbd2/transaction.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -532,6 +532,7 @@ int jbd2_journal_start_reserved(handle_t *handle, unsigned int type,
		*/
		ret = start_this_handle(journal, handle, GFP_NOFS);
		if (ret < 0) {
		handle->h_journal = journal;
		jbd2_journal_free_reserved(handle);
		return ret;
		}

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