On Mon 17-09-18 04:19:02, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 2e2a0c961a87 Merge branch 'progarray_mapinmap_dump' > git tree: bpf-next > console output: https://syzkaller.appspot.com/x/log.txt?x=17622811400000 > kernel config: https://syzkaller.appspot.com/x/.config?x=8f59875069d721b6 > dashboard link: https://syzkaller.appspot.com/bug?extid=7f4a27091759e2fe7453 > compiler: gcc (GCC) 8.0.1 20180413 (experimental) > > Unfortunately, I don't have any reproducer for this crash yet. > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+7f4a27091759e2fe7453@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KASAN: use-after-free in atomic_inc > include/asm-generic/atomic-instrumented.h:109 [inline] > BUG: KASAN: use-after-free in get_bh include/linux/buffer_head.h:283 > [inline] > BUG: KASAN: use-after-free in jbd2_log_do_checkpoint+0x113d/0x13e0 > fs/jbd2/checkpoint.c:337 > Write of size 4 at addr ffff8801b6d96300 by task syz-executor1/904 This is at: if (buffer_locked(bh)) { spin_unlock(&journal->j_list_lock); get_bh(bh); wait_on_buffer(bh); /* the journal_head may have gone by now */ BUFFER_TRACE(bh, "brelse"); __brelse(bh); spin_lock(&journal->j_list_lock); goto restart2; } And indeed that get_bh() should be called before we unlock j_list_lock as otherwise we can race with jbd2_journal_try_to_free_buffers(). I'll send a fix. Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
