On Wed, Dec 20, 2017 at 8:59 AM, Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > On Wed, Dec 20, 2017 at 08:50:40AM +0100, Dmitry Vyukov wrote: >> > >> > The line number in lib/rbtree.c seems to be slightly off. Looking at the >> > disassembly: >> > >> > ffffffff825b5ea0 <rb_insert_color>: >> > ffffffff825b5ea0: 55 push %rbp >> > ffffffff825b5ea1: 48 8b 17 mov (%rdi),%rdx >> > ffffffff825b5ea4: 48 89 e5 mov %rsp,%rbp >> > ffffffff825b5ea7: 48 85 d2 test %rdx,%rdx >> > ffffffff825b5eaa: 0f 84 4c 01 00 00 je ffffffff825b5ffc <rb_insert_color+0x15c> >> > ffffffff825b5eb0: 48 8b 02 mov (%rdx),%rax >> > ffffffff825b5eb3: a8 01 test $0x1,%al >> > ffffffff825b5eb5: 75 5e jne ffffffff825b5f15 <rb_insert_color+0x75> >> > ffffffff825b5eb7: 48 8b 48 08 mov 0x8(%rax),%rcx >> > >> > It crashed on 'mov 0x8(%rax),%rcx' which corresponds to >> > 'tmp = gparent->rb_right;' at lib/rbtree.c:131. So 'parent' was the root node, >> > but its color was red, while it is supposed to be black. >> > >> > No idea how that happened, but it's almost certainly not an ext4 bug. In fact >> > there is another report of this same crash that has a different call trace: >> > >> > Call Trace: >> > key_alloc_serial security/keys/key.c:170 [inline] >> > key_alloc+0x54c/0x5b0 security/keys/key.c:319 >> > keyring_alloc+0x4d/0xb0 security/keys/keyring.c:503 >> > install_process_keyring_to_cred.part.3+0x38/0x80 security/keys/process_keys.c:192 >> > install_process_keyring_to_cred security/keys/process_keys.c:634 [inline] >> > install_process_keyring security/keys/process_keys.c:217 [inline] >> > lookup_user_key+0x4ed/0x7c0 security/keys/process_keys.c:574 >> > SYSC_add_key security/keys/keyctl.c:114 [inline] >> > SyS_add_key+0xec/0x260 security/keys/keyctl.c:62 >> > entry_SYSCALL_64_fastpath+0x1f/0x96 >> >> >> My first hypothesis for an non-explainable, non-reproducible >> corruption would be a data race. Is there all locking in place? > > It doesn't seem to be a locking problem. In the ext4 case the rbtree is > associated with a struct file's dir_private_info, which is protected by > ->f_pos_lock (taken early in sys_getdents()). But this won't prevent somebody else to mess with the struct without taking the lock. > And in the keyrings case, the > rbtree is protected by key_serial_lock.
