Syzkaller reported a KASAN slab-out-of-bounds write in __bpf_get_stackid() when copying stack trace data. The issue occurs when the perf trace contains more stack entries than the stack map bucket can hold, leading to an out-of-bounds write in the bucket's data array. Changes in v2: - Fixed max_depth names across get stack id Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b Signed-off-by: Arnaud Lecomte --- kernel/bpf/stackmap.c | 24 ++++++++++++++---------- 1 file changed, 14 insertions(+), 10 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index a267567e36dd..e1ee18cbbbb2 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -246,7 +246,7 @@ get_callchain_entry_for_task(struct task_struct *task, u32 max_depth) } static long __bpf_get_stackid(struct bpf_map *map, - struct perf_callchain_entry *trace, u64 flags) + struct perf_callchain_entry *trace, u64 flags, u32 max_depth) { struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); struct stack_map_bucket *bucket, *new_bucket, *old_bucket; @@ -262,6 +262,8 @@ static long __bpf_get_stackid(struct bpf_map *map, trace_nr = trace->nr - skip; trace_len = trace_nr * sizeof(u64); + trace_nr = min(trace_nr, max_depth - skip); + ips = trace->ip + skip; hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); id = hash & (smap->n_buckets - 1); @@ -321,19 +323,17 @@ static long __bpf_get_stackid(struct bpf_map *map, BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, u64, flags) { - u32 max_depth = map->value_size / stack_map_data_size(map); - u32 skip = flags & BPF_F_SKIP_FIELD_MASK; + u32 elem_size = stack_map_data_size(map); bool user = flags & BPF_F_USER_STACK; struct perf_callchain_entry *trace; bool kernel = !user; + u32 max_depth; if (unlikely(flags & ~(BPF_F_SKIP_FIELD_MASK | BPF_F_USER_STACK | BPF_F_FAST_STACK_CMP | BPF_F_REUSE_STACKID))) return -EINVAL; - max_depth += skip; - if (max_depth > sysctl_perf_event_max_stack) - max_depth = sysctl_perf_event_max_stack; + max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags); trace = get_perf_callchain(regs, 0, kernel, user, max_depth, false, false); @@ -342,7 +342,7 @@ BPF_CALL_3(bpf_get_stackid, struct pt_regs *, regs, struct bpf_map *, map, /* couldn't fetch the stack trace */ return -EFAULT; - return __bpf_get_stackid(map, trace, flags); + return __bpf_get_stackid(map, trace, flags, max_depth); } const struct bpf_func_proto bpf_get_stackid_proto = { @@ -374,6 +374,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, bool kernel, user; __u64 nr_kernel; int ret; + u32 elem_size, max_depth; /* perf_sample_data doesn't have callchain, use bpf_get_stackid */ if (!(event->attr.sample_type & PERF_SAMPLE_CALLCHAIN)) @@ -392,16 +393,18 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, return -EFAULT; nr_kernel = count_kernel_ip(trace); - + elem_size = stack_map_data_size(map); if (kernel) { __u64 nr = trace->nr; trace->nr = nr_kernel; - ret = __bpf_get_stackid(map, trace, flags); + max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags); + ret = __bpf_get_stackid(map, trace, flags, max_depth); /* restore nr */ trace->nr = nr; } else { /* user */ + u64 skip = flags & BPF_F_SKIP_FIELD_MASK; skip += nr_kernel; @@ -409,7 +412,8 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, return -EFAULT; flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip; - ret = __bpf_get_stackid(map, trace, flags); + max_depth = stack_map_calculate_max_depth(map->value_size, elem_size, flags); + ret = __bpf_get_stackid(map, trace, flags, max_depth); } return ret; } -- 2.43.0