From: Xu Yu xuyu@linux.alibaba.com

[ upstream commit 0803278b0b4d8eeb2b461fb698785df65a725d9e ]

Syzkaller hit 'KASAN: use-after-free Write in sanitize_ptr_alu' bug.

Call trace:

dump_stack+0xbf/0x12e print_address_description+0x6a/0x280 kasan_report+0x237/0x360 sanitize_ptr_alu+0x85a/0x8d0 adjust_ptr_min_max_vals+0x8f2/0x1ca0 adjust_reg_min_max_vals+0x8ed/0x22e0 do_check+0x1ca6/0x5d00 bpf_check+0x9ca/0x2570 bpf_prog_load+0xc91/0x1030 __se_sys_bpf+0x61e/0x1f00 do_syscall_64+0xc8/0x550 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Fault injection trace:

kfree+0xea/0x290  free_func_state+0x4a/0x60  free_verifier_state+0x61/0xe0  push_stack+0x216/0x2f0 <- inject failslab  sanitize_ptr_alu+0x2b1/0x8d0  adjust_ptr_min_max_vals+0x8f2/0x1ca0  adjust_reg_min_max_vals+0x8ed/0x22e0  do_check+0x1ca6/0x5d00  bpf_check+0x9ca/0x2570  bpf_prog_load+0xc91/0x1030  __se_sys_bpf+0x61e/0x1f00  do_syscall_64+0xc8/0x550  entry_SYSCALL_64_after_hwframe+0x49/0xbe

When kzalloc() fails in push_stack(), free_verifier_state() will free current verifier state. As push_stack() returns, dst_reg was restored if ptr_is_dst_reg is false. However, as member of the cur_state, dst_reg is also freed, and error occurs when dereferencing dst_reg. Simply fix it by testing ret of push_stack() before restoring dst_reg.

Fixes: 979d63d50c0c ("bpf: prevent out of bounds speculation on pointer arithmetic") Signed-off-by: Xu Yu xuyu@linux.alibaba.com Signed-off-by: Daniel Borkmann daniel@iogearbox.net --- kernel/bpf/verifier.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index bcb42aa..acc2305 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -2815,7 +2815,7 @@ static int sanitize_ptr_alu(struct bpf_verifier_env *env, *dst_reg = *ptr_reg; } ret = push_stack(env, env->insn_idx + 1, env->insn_idx, true); - if (!ptr_is_dst_reg) + if (!ptr_is_dst_reg && ret) *dst_reg = tmp; return !ret ? -EFAULT : 0; }