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Commit f1213cac authored by Abhijith Das's avatar Abhijith Das Committed by Steven Whitehouse
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GFS2: Fix race in gfs2_rs_alloc 



QE aio tests uncovered a race condition in gfs2_rs_alloc where it's possible
to come out of the function with a valid ip->i_res allocation but it gets
freed before use resulting in a NULL ptr dereference.

This patch envelopes the initial short-circuit check for non-NULL ip->i_res
into the mutex lock. With this patch, I was able to successfully run the
reproducer test multiple times.

Resolves: rhbz#878476
Signed-off-by: default avatarAbhi Das <adas@redhat.com>
Signed-off-by: default avatarSteven Whitehouse <swhiteho@redhat.com>
parent ec148752

fs/gfs2/rgrp.c

+10 −12
Original line number Diff line number Diff line
@@ -557,22 +557,20 @@ void gfs2_free_clones(struct gfs2_rgrpd *rgd) 
 */

int gfs2_rs_alloc(struct gfs2_inode *ip)

{

	struct gfs2_blkreserv *res;

	int error = 0;



	down_write(&ip->i_rw_mutex);

	if (ip->i_res)

		return 0;



	res = kmem_cache_zalloc(gfs2_rsrv_cachep, GFP_NOFS);

	if (!res)

		return -ENOMEM;

		goto out;



	RB_CLEAR_NODE(&res->rs_node);

	ip->i_res = kmem_cache_zalloc(gfs2_rsrv_cachep, GFP_NOFS);

	if (!ip->i_res) {

		error = -ENOMEM;

		goto out;

	}



	down_write(&ip->i_rw_mutex);

	if (ip->i_res)

		kmem_cache_free(gfs2_rsrv_cachep, res);

	else

		ip->i_res = res;

	RB_CLEAR_NODE(&ip->i_res->rs_node);

out:

	up_write(&ip->i_rw_mutex);

	return 0;

}