BPF_OBJ_GET_INFO_BY_FD for bpf_link copies struct bpf_link_info back to
userspace only when ->fill_link_info() succeeds. Some link info providers,
however, can return -ENOSPC after computing valid metadata when a nested
userspace output buffer is too small.
For example, perf event tracepoint link info can determine the required
tp_name length before copying the name fails with -ENOSPC. The current
top-level error handling returns immediately in that case, so userspace
observes -ENOSPC but loses the metadata needed to retry with a sufficiently
large buffer.
Allow bpf_link_get_info_by_fd() to copy the top-level bpf_link_info back
on -ENOSPC, while still returning -ENOSPC to userspace. Also let perf
event kprobe, uprobe, and tracepoint link info fill their metadata before
returning -ENOSPC from nested name buffer copying.
Fixes: f2e10bff16a0 ("bpf: Add support for BPF_OBJ_GET_INFO_BY_FD for bpf_link")
Fixes: 1b715e1b0ec5 ("bpf: Support ->fill_link_info for perf_event")
Signed-off-by: Sun Jian <[email protected]>
---
kernel/bpf/syscall.c | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index 6db306d23b47..80ab02b1c813 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -4060,7 +4060,7 @@ static int bpf_perf_link_fill_kprobe(const struct
perf_event *event,
ulen = info->perf_event.kprobe.name_len;
err = bpf_perf_link_fill_common(event, uname, &ulen, &offset, &addr,
&type, &missed);
- if (err)
+ if (err && err != -ENOSPC)
return err;
if (type == BPF_FD_TYPE_KRETPROBE)
info->perf_event.type = BPF_PERF_EVENT_KRETPROBE;
@@ -4073,7 +4073,7 @@ static int bpf_perf_link_fill_kprobe(const struct
perf_event *event,
addr = 0;
info->perf_event.kprobe.addr = addr;
info->perf_event.kprobe.cookie = event->bpf_cookie;
- return 0;
+ return err;
}
static void bpf_perf_link_fdinfo_kprobe(const struct perf_event *event,
@@ -4116,7 +4116,7 @@ static int bpf_perf_link_fill_uprobe(const struct
perf_event *event,
ulen = info->perf_event.uprobe.name_len;
err = bpf_perf_link_fill_common(event, uname, &ulen, &offset,
&ref_ctr_offset,
&type, NULL);
- if (err)
+ if (err && err != -ENOSPC)
return err;
if (type == BPF_FD_TYPE_URETPROBE)
@@ -4127,7 +4127,7 @@ static int bpf_perf_link_fill_uprobe(const struct
perf_event *event,
info->perf_event.uprobe.offset = offset;
info->perf_event.uprobe.cookie = event->bpf_cookie;
info->perf_event.uprobe.ref_ctr_offset = ref_ctr_offset;
- return 0;
+ return err;
}
static void bpf_perf_link_fdinfo_uprobe(const struct perf_event *event,
@@ -4180,13 +4180,13 @@ static int bpf_perf_link_fill_tracepoint(const struct
perf_event *event,
uname = u64_to_user_ptr(info->perf_event.tracepoint.tp_name);
ulen = info->perf_event.tracepoint.name_len;
err = bpf_perf_link_fill_common(event, uname, &ulen, NULL, NULL, NULL,
NULL);
- if (err)
+ if (err && err != -ENOSPC)
return err;
info->perf_event.type = BPF_PERF_EVENT_TRACEPOINT;
info->perf_event.tracepoint.name_len = ulen;
info->perf_event.tracepoint.cookie = event->bpf_cookie;
- return 0;
+ return err;
}
static int bpf_perf_link_fill_perf_event(const struct perf_event *event,
@@ -5536,7 +5536,7 @@ static int bpf_link_get_info_by_fd(struct file *file,
struct bpf_link_info __user *uinfo = u64_to_user_ptr(attr->info.info);
struct bpf_link_info info;
u32 info_len = attr->info.info_len;
- int err;
+ int err = 0;
err = bpf_check_uarg_tail_zero(USER_BPFPTR(uinfo), sizeof(info),
info_len);
if (err)
@@ -5554,7 +5554,7 @@ static int bpf_link_get_info_by_fd(struct file *file,
if (link->ops->fill_link_info) {
err = link->ops->fill_link_info(link, &info);
- if (err)
+ if (err && err != -ENOSPC)
return err;
}
@@ -5562,7 +5562,7 @@ static int bpf_link_get_info_by_fd(struct file *file,
put_user(info_len, &uattr->info.info_len))
return -EFAULT;
- return 0;
+ return err;
}
--
2.43.0
