From: Rong Tao <[email protected]>
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, indicating a successful match.
Fixes: e91370550f1f ("bpf: Add kfuncs for read-only string operations")
Signed-off-by: Rong Tao <[email protected]>
---
kernel/bpf/helpers.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..bf04881f96ec 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3672,10 +3672,18 @@ __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;
+ /**
+ * corner case i+j==len to ensure that we matched
+ * entire s2. for example, param len=3:
+ * s1: A B C D E F -> i==1
+ * s2: B C D -> j==2
+ */
+ if (i + j == len)
+ break;
__get_kernel_nofault(&c1, s1__ign + j, char, err_out);
if (c1 == '\0')
return -ENOENT;
--
2.51.0
