Commit 08fc98a4 authored May 10, 2019 by Sahitya Tummala Committed by Theodore Ts'o May 10, 2019

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



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: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Andreas Dilger <adilger@dilger.ca>
Cc: stable@kernel.org

parent 57a0da28

fs/ext4/namei.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -872,12 +872,15 @@ 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);

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