[PATCH bpf v1 1/2] bpf: fix unpopulated path_size when uprobe_multi fields unset

Tyrone Wu
2024-10-09T22:07:00Z

Previously when retrieving `bpf_link_info.uprobe_multi` with `path` and
`path_size` fields unset, the `path_size` field is not populated
(remains 0). This behavior was inconsistent with how other input/output
string buffer fields work, as the field should be populated in cases
when:
- both buffer and length are set (currently works as expected)
- both buffer and length are unset (not working as expected)

This patch now fills the `path_size` field when `path` and `path_size`
are unset.

Fixes: e56fdbfb06e2 ("bpf: Add link_info support for uprobe multi link")
Signed-off-by: Tyrone Wu <wudevelops@gmail.com>
---
kernel/trace/bpf_trace.c | 35 +++++++++++++++++------------------
1 file changed, 17 insertions(+), 18 deletions(-)

diff --git a/kernel/trace/bpf_trace.c b/kernel/trace/bpf_trace.c
index a582cd25ca87..ba34e4f3fa8f 100644
--- a/kernel/trace/bpf_trace.c
+++ b/kernel/trace/bpf_trace.c
@@ -3133,7 +3133,8 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
struct bpf_uprobe_multi_link *umulti_link;
u32 ucount = info->uprobe_multi.count;
int err = 0, i;
- long left;
+ char *p, *buf;
+ long left = 0;

if (!upath ^ !upath_size)
return -EINVAL;
@@ -3147,26 +3148,24 @@ static int bpf_uprobe_multi_link_fill_link_info(const struct bpf_link *link,
info->uprobe_multi.pid = umulti_link->task ?
task_pid_nr_ns(umulti_link->task, task_active_pid_ns(current)) : 0;

- if (upath) {
- char *p, *buf;
-
- upath_size = min_t(u32, upath_size, PATH_MAX);
+ upath_size = upath_size ? min_t(u32, upath_size, PATH_MAX) : PATH_MAX;
+ buf = kmalloc(upath_size, GFP_KERNEL);
+ if (!buf)
+ return -ENOMEM;
+ p = d_path(&umulti_link->path, buf, upath_size);
+ if (IS_ERR(p)) {
+ kfree(buf);
+ return PTR_ERR(p);
+ }
+ upath_size = buf + upath_size - p;

- buf = kmalloc(upath_size, GFP_KERNEL);
- if (!buf)
- return -ENOMEM;
- p = d_path(&umulti_link->path, buf, upath_size);
- if (IS_ERR(p)) {
- kfree(buf);
- return PTR_ERR(p);
- }
- upath_size = buf + upath_size - p;
+ if (upath) {
left = copy_to_user(upath, p, upath_size);
- kfree(buf);
- if (left)
- return -EFAULT;
- info->uprobe_multi.path_size = upath_size;
}
+ kfree(buf);
+ if (left)
+ return -EFAULT;
+ info->uprobe_multi.path_size = upath_size;

if (!uoffsets && !ucookies && !uref_ctr_offsets)
return 0;
--
2.43.0