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Fix bpf_strnstr len error #5861

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Fix bpf_strnstr len error #5861

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0715f71
bpf/helpers: bpf_strnstr: Exact match length
Rtoax Aug 29, 2025
0100b17
selftests/bpf: Add tests for bpf_strnstr
Rtoax Aug 29, 2025
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9 changes: 8 additions & 1 deletion kernel/bpf/helpers.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
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8 changes: 6 additions & 2 deletions tools/testing/selftests/bpf/progs/string_kfuncs_success.c
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Expand Up @@ -30,8 +30,12 @@ __test(2) int test_strcspn(void *ctx) { return bpf_strcspn(str, "lo"); }
__test(6) int test_strstr_found(void *ctx) { return bpf_strstr(str, "world"); }
__test(-ENOENT) int test_strstr_notfound(void *ctx) { return bpf_strstr(str, "hi"); }
__test(0) int test_strstr_empty(void *ctx) { return bpf_strstr(str, ""); }
__test(0) int test_strnstr_found(void *ctx) { return bpf_strnstr(str, "hello", 6); }
__test(-ENOENT) int test_strnstr_notfound(void *ctx) { return bpf_strnstr(str, "hi", 10); }
__test(0) int test_strnstr_found1(void *ctx) { return bpf_strnstr("", "", 0); }
__test(0) int test_strnstr_found2(void *ctx) { return bpf_strnstr(str, "hello", 5); }
__test(0) int test_strnstr_found3(void *ctx) { return bpf_strnstr(str, "hello", 6); }
__test(-ENOENT) int test_strnstr_notfound1(void *ctx) { return bpf_strnstr(str, "hi", 10); }
__test(-ENOENT) int test_strnstr_notfound2(void *ctx) { return bpf_strnstr(str, "hello", 4); }
__test(-ENOENT) int test_strnstr_notfound3(void *ctx) { return bpf_strnstr("", "a", 0); }
__test(0) int test_strnstr_empty(void *ctx) { return bpf_strnstr(str, "", 1); }

char _license[] SEC("license") = "GPL";
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