From 08fc98a4d6424af66eb3ac4e2cedd2fc927ed436 Mon Sep 17 00:00:00 2001
From: Sahitya Tummala <stummala@codeaurora.org>
Date: Fri, 10 May 2019 22:00:33 -0400
Subject: [PATCH] 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
---
fs/ext4/namei.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index e917830eae84d..ac7457fef9e63 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -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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