On Fri, Aug 29, 2025 at 9:32 AM Rong Tao rtoax@foxmail.com wrote:
From: Rong Tao rongtao@cestc.cn
I reworded patch subject a bit, please check the final version
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) = 0This 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@cestc.cn
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;/**
fixed up comment style (extra *) when applying to bpf tree, thanks.
* 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