On 8/11/24 16:54, Jordan Rome wrote:
This adds a kfunc wrapper around strncpy_from_user,
which can be called from sleepable BPF programs.
This matches the non-sleepable 'bpf_probe_read_user_str'
helper.
Signed-off-by: Jordan Rome <linux@xxxxxxxxxxxxxx>
---
kernel/bpf/helpers.c | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index d02ae323996b..5eeb7c2ca622 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -2939,6 +2939,37 @@ __bpf_kfunc void bpf_iter_bits_destroy(struct bpf_iter_bits *it)
bpf_mem_free(&bpf_global_ma, kit->bits);
}
+/**
+ * bpf_copy_from_user_str() - Copy a string from an unsafe user address
+ * @dst: Destination address, in kernel space. This buffer must be at
+ * least @dst__szk bytes long.
+ * @dst__szk: Maximum number of bytes to copy, including the trailing NUL.
+ * @unsafe_ptr__ign: Source address, in user space.
+ *
+ * Copies a NUL-terminated string from userspace to BPF space. If user string is
+ * too long this will still ensure zero termination in the dst buffer unless
+ * buffer size is 0.
+ */
+__bpf_kfunc int bpf_copy_from_user_str(void *dst, u32 dst__szk, const void __user *unsafe_ptr__ign)
+{
+ int ret;
+
+ if (unlikely(!dst__szk))
+ return 0;
+
+ ret = strncpy_from_user(dst, unsafe_ptr__ign, dst__szk);
+ if (unlikely(ret < 0)) {
+ memset(dst, 0, dst__szk);
+ } else if (ret >= dst__szk) {
+ ret = dst__szk;
+ ((char *)dst)[ret - 1] = '\0';
+ } else if (ret > 0) {
+ ret++;
I prefer to keep consistent with strncpy_from_user().
Considering ret >= dst__szk, it is not actually copying dst__szk bytes.
The last byte is generated by this function, not copying from
the source buffer.
Copying at most dst__szk - 1 bytes is more concise.
The code could be simpler with this concept.
ret = strncpy_from_user(dst, unsafe_ptr__ign, dst_szk - 1);
((char *)dst)[max(ret, 0)] = 0;
WDYT?
+ }
+
+ return ret;
+}
+
__bpf_kfunc_end_defs();
BTF_KFUNCS_START(generic_btf_ids)
@@ -3024,6 +3055,7 @@ BTF_ID_FLAGS(func, bpf_preempt_enable)
BTF_ID_FLAGS(func, bpf_iter_bits_new, KF_ITER_NEW)
BTF_ID_FLAGS(func, bpf_iter_bits_next, KF_ITER_NEXT | KF_RET_NULL)
BTF_ID_FLAGS(func, bpf_iter_bits_destroy, KF_ITER_DESTROY)
+BTF_ID_FLAGS(func, bpf_copy_from_user_str, KF_SLEEPABLE)
BTF_KFUNCS_END(common_btf_ids)
static const struct btf_kfunc_id_set common_kfunc_set = {
--
2.44.1
