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

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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
This commit is contained in:
Sahitya Tummala 2019-05-10 22:00:33 -04:00 committed by Theodore Ts'o
parent 57a0da28ce
commit 08fc98a4d6
1 changed files with 4 additions and 1 deletions
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5
fs/ext4/namei.c
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@ -872,12 +872,15 @@ static void dx_release(struct dx_frame *frames)
{ {
struct dx_root_info *info; struct dx_root_info *info;
int i; int i;
unsigned int indirect_levels;
if (frames[0].bh == NULL) if (frames[0].bh == NULL)
return; return;
info = &((struct dx_root *)frames[0].bh->b_data)->info; 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) if (frames[i].bh == NULL)
break; break;
brelse(frames[i].bh); brelse(frames[i].bh);