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bpf: Fix stackmap overflow check in __bpf_get_stackid()

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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.

Fixes: ee2a098851 ("bpf: Adjust BPF stack helper functions to accommodate skip > 0")
Reported-by: syzbot+c9b724fbb41cf2538b7b@syzkaller.appspotmail.com
Signed-off-by: Arnaud Lecomte <contact@arnaud-lcm.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yonghong.song@linux.dev>
Acked-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/bpf/20251025192941.1500-1-contact@arnaud-lcm.com

Closes: https://syzkaller.appspot.com/bug?extid=c9b724fbb41cf2538b7b
This commit is contained in:
Arnaud Lecomte 2025-10-25 19:29:41 +00:00 committed by Andrii Nakryiko
parent e17d62fedd
commit 23f852daa4
1 changed files with 8 additions and 7 deletions
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15
kernel/bpf/stackmap.c
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@ -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 bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
struct stack_map_bucket *bucket, *new_bucket, *old_bucket; struct stack_map_bucket *bucket, *new_bucket, *old_bucket;
u32 hash, id, trace_nr, trace_len, i, max_depth;
u32 skip = flags & BPF_F_SKIP_FIELD_MASK; u32 skip = flags & BPF_F_SKIP_FIELD_MASK;
u32 hash, id, trace_nr, trace_len, i;
bool user = flags & BPF_F_USER_STACK; bool user = flags & BPF_F_USER_STACK;
u64 *ips; u64 *ips;
bool hash_matches; bool hash_matches;
@ -261,7 +261,8 @@ static long __bpf_get_stackid(struct bpf_map *map,
/* skipping more than usable stack trace */ /* skipping more than usable stack trace */
return -EFAULT; return -EFAULT;
trace_nr = trace->nr - skip; max_depth = stack_map_calculate_max_depth(map->value_size, stack_map_data_size(map), flags);
trace_nr = min_t(u32, trace->nr - skip, max_depth - skip);
trace_len = trace_nr * sizeof(u64); trace_len = trace_nr * sizeof(u64);
ips = trace->ip + skip; ips = trace->ip + skip;
hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0); hash = jhash2((u32 *)ips, trace_len / sizeof(u32), 0);
@ -390,15 +391,11 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
return -EFAULT; return -EFAULT;
nr_kernel = count_kernel_ip(trace); nr_kernel = count_kernel_ip(trace);
__u64 nr = trace->nr; /* save original */
if (kernel) { if (kernel) {
__u64 nr = trace->nr;
trace->nr = nr_kernel; trace->nr = nr_kernel;
ret = __bpf_get_stackid(map, trace, flags); ret = __bpf_get_stackid(map, trace, flags);
/* restore nr */
trace->nr = nr;
} else { /* user */ } else { /* user */
u64 skip = flags & BPF_F_SKIP_FIELD_MASK; u64 skip = flags & BPF_F_SKIP_FIELD_MASK;
@ -409,6 +406,10 @@ BPF_CALL_3(bpf_get_stackid_pe, struct bpf_perf_event_data_kern *, ctx,
flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip; flags = (flags & ~BPF_F_SKIP_FIELD_MASK) | skip;
ret = __bpf_get_stackid(map, trace, flags); ret = __bpf_get_stackid(map, trace, flags);
} }
/* restore nr */
trace->nr = nr;
return ret; return ret;
} }