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. Reported-by: syzbot+c9b724fbb41cf2538b7b@xxxxxxxxxxxxxxxxxxxxxxxxx Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b Fixes: ee2a098851bf ("bpf: Adjust BPF stack helper functions to accommodate skip > 0") Acked-by: Yonghong Song <yonghong.song@xxxxxxxxx> Acked-by: Song Liu <song@xxxxxxxxxx> Signed-off-by: Arnaud Lecomte <contact@xxxxxxxxxxxxxx> --- Changes in v2: - Fixed max_depth names across get stack id Changes in v4: - Removed unnecessary empty line in __bpf_get_stackid Changes in v6: - Added back trace_len computation in __bpf_get_stackid Changes in v7: - Removed usefull trace->nr assignation in bpf_get_stackid_pe - Added restoration of trace->nr for both kernel and user traces in bpf_get_stackid_pe Changes in v9: - Fixed variable declarations in bpf_get_stackid_pe - Added the missing truncate of trace_nr in __bpf_getstackid Link to v8: https://lore.kernel.org/all/20250905134833.26791-1-contact@xxxxxxxxxxxxxx/ --- --- kernel/bpf/stackmap.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c index 9a86b5acac10..ac5ec3253ce6 100644 --- a/kernel/bpf/stackmap.c +++ b/kernel/bpf/stackmap.c @@ -251,8 +251,8 @@ static long __bpf_get_stackid(struct bpf_map *map, { struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map); struct stack_map_bucket *bucket, *new_bucket, *old_bucket; + u32 hash, id, trace_nr, trace_len, i, max_storable; u32 skip = flags & BPF_F_SKIP_FIELD_MASK; - u32 hash, id, trace_nr, trace_len, i; bool user = flags & BPF_F_USER_STACK; u64 *ips; bool hash_matches; @@ -261,7 +261,9 @@ static long __bpf_get_stackid(struct bpf_map *map, /* skipping more than usable stack trace */ return -EFAULT; + max_storable = map->value_size / stack_map_data_size(map); trace_nr = trace->nr - skip; + trace_nr = min_t(u32, trace_nr, max_storable); trace_len = trace_nr * sizeof(u64); ips = trace->ip + skip; hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); @@ -369,6 +371,7 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, { struct perf_event *event = ctx->event; struct perf_callchain_entry *trace; + u32 elem_size, max_depth; bool kernel, user; __u64 nr_kernel; int ret; @@ -390,15 +393,16 @@ 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); + __u64 nr = trace->nr; /* save original */ if (kernel) { - __u64 nr = trace->nr; - trace->nr = nr_kernel; + max_depth = + stack_map_calculate_max_depth(map->value_size, elem_size, flags); + trace->nr = min_t(u32, nr_kernel, max_depth); ret = __bpf_get_stackid(map, trace, flags); - /* restore nr */ - trace->nr = nr; } else { /* user */ u64 skip = flags & BPF_F_SKIP_FIELD_MASK; @@ -407,8 +411,15 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx, return -EFAULT; flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip; + max_depth = + stack_map_calculate_max_depth(map->value_size, elem_size, flags); + trace->nr = min_t(u32, trace->nr, max_depth); ret = __bpf_get_stackid(map, trace, flags); } + + /* restore nr */ + trace->nr = nr; + return ret; } -- 2.43.0
