The patch below does not apply to the 4.9-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
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
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c index e917830eae84..ac7457fef9e6 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);