On 8/28/25 06:35, Andrii Nakryiko wrote:
cc'ing Viktor as well
On Tue, Aug 26, 2025 at 9:29 PM Rong Tao <rtoax@xxxxxxxxxxx> wrote:
From: Rong Tao <rongtao@xxxxxxxx>
strnstr should not treat the ending '\0' of s2 as a matching character,
otherwise the parameter 'len' will be meaningless, for example:
1. bpf_strnstr("openat", "open", 4) = -ENOENT
2. bpf_strnstr("openat", "open", 5) = 0
please add these cases to the tests
This patch makes (1) return 0, indicating a successful match.
Signed-off-by: Rong Tao <rongtao@xxxxxxxx>
---
kernel/bpf/helpers.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..65bd0050c560 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3681,6 +3681,8 @@ __bpf_kfunc int bpf_strnstr(const char *s1__ign, const char *s2__ign, size_t len
return -ENOENT;
if (c1 != c2)
break;
+ if (j == len - 1)
+ return i;
But this seems like a wrong fix. The API assumes that s2 is
Thanks a lot Andrii Nakryiko, I just submit V2, please review.
well-formed zero-terminated string, and so we shouldn't just randomly
truncate it. Along the examples above, what will happen to
bpf_strnstr("openat", "open", 3)? With your fix it will return
success, right? But it shouldn't, IMO, because "open" wasn't really
found in the first 3 characters of, effectively, "ope".
We should also test bpf_strnstr("", "", 0)... ;)
So maybe something like this (but I haven't really tested it):
diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 401b4932cc49..ced7132980fe 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -3672,10 +3672,12 @@ __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;
+ if (i + j == len)
+ break;
It's works fine, thanks.
__get_kernel_nofault(&c1, s1__ign + j, char, err_out);
if (c1 == '\0')
return -ENOENT;
pw-bot: cr
}
if (j == XATTR_SIZE_MAX)
return -E2BIG;
--
2.51.0
