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Commit c19db366 authored by Sahitya Tummala's avatar Sahitya Tummala Committed by Greg Kroah-Hartman
Browse files

ext4: fix use-after-free in dx_release() 



commit 08fc98a4d6424af66eb3ac4e2cedd2fc927ed436 upstream.

The buffer_head (frames[0].bh) and it's corresping page can be
potentially free'd once brelse() is done inside the for loop
but before the for loop exits in dx_release(). It can be free'd
in another context, when the page cache is flushed via
drop_caches_sysctl_handler(). This results into below data abort
when accessing info->indirect_levels in dx_release().

Unable to handle kernel paging request at virtual address ffffffc17ac3e01e
Call trace:
 dx_release+0x70/0x90
 ext4_htree_fill_tree+0x2d4/0x300
 ext4_readdir+0x244/0x6f8
 iterate_dir+0xbc/0x160
 SyS_getdents64+0x94/0x174

Signed-off-by: default avatarSahitya Tummala <stummala@codeaurora.org>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Reviewed-by: default avatarAndreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0db24122

fs/ext4/namei.c

+4 −1
Original line number Diff line number Diff line
@@ -871,12 +871,15 @@ static void dx_release(struct dx_frame *frames) 
{

	struct dx_root_info *info;

	int i;

	unsigned int indirect_levels;



	if (frames[0].bh == NULL)

		return;



	info = &((struct dx_root *)frames[0].bh->b_data)->info;

	for (i = 0; i <= info->indirect_levels; i++) {

	/* save local copy, "info" may be freed after brelse() */

	indirect_levels = info->indirect_levels;

	for (i = 0; i <= indirect_levels; i++) {

		if (frames[i].bh == NULL)

			break;

		brelse(frames[i].bh);