From: Sahitya Tummala stummala@codeaurora.org
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: 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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/ext4/namei.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/fs/ext4/namei.c +++ b/fs/ext4/namei.c @@ -871,12 +871,15 @@ static void dx_release(struct dx_frame * { 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);