From: Rong Tao <rongtao@xxxxxxxx>
strnstr should not treat the ending '\0' of s2 as a matching character
if the parameter 'len' equal to s2 string length, for example:
1. bpf_strnstr("openat", "open", 4) = -ENOENT
2. bpf_strnstr("openat", "open", 5) = 0
This patch makes (1) return 0, fix just the `len == strlen(s2)` case.
And fix a more general case when s2 is a suffix of the first len
characters of s1.
Fixes: e91370550f1f ("bpf: Add kfuncs for read-only string operations")
Signed-off-by: Rong Tao <rongtao@xxxxxxxx>
---
kernel/bpf/helpers.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..91ad124844ae 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3672,10 +3672,17 @@ __bpf_kfunc int bpf_strnstr(const char *s1__ign, const char *s2__ign, size_t len
guard(pagefault)();
for (i = 0; i < XATTR_SIZE_MAX; i++) {
- for (j = 0; i + j < len && j < XATTR_SIZE_MAX; j++) {
+ for (j = 0; i + j <= len && j < XATTR_SIZE_MAX; j++) {
__get_kernel_nofault(&c2, s2__ign + j, char, err_out);
if (c2 == '\0')
return i;
+ /**
+ * We allow reading an extra byte from s2 (note the
+ * `i + j <= len` above) to cover the case when s2 is
+ * a suffix of the first len chars of s1.
+ */
+ if (i + j == len)
+ break;
__get_kernel_nofault(&c1, s1__ign + j, char, err_out);
if (c1 == '\0')
return -ENOENT;
--
2.51.0
