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bpf: strnchr not suitable for getting NUL-terminator

Message ID tencent_EC72CD3879FA6F102FC56E4495F0E822EC0A@qq.com (mailing list archive)
State Not Applicable
Delegated to: BPF
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Series bpf: strnchr not suitable for getting NUL-terminator | expand

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Commit Message

Edward Adam Davis April 10, 2024, 12:33 a.m. UTC 
The strnchr() is not suitable for obtaining the end of a string with a length
exceeding 1 and ending with a NUL character.

Signed-off-by: Edward Adam Davis <eadavis@qq.com>
---
 kernel/bpf/helpers.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

Yonghong Song April 10, 2024, 3:09 p.m. UTC | #1 
On 4/9/24 5:33 PM, Edward Adam Davis wrote:
> The strnchr() is not suitable for obtaining the end of a string with a length
> exceeding 1 and ending with a NUL character.

Could you give more detailed explanation with specific examples? I think
strnchr() does the right thing here. Note that if fmt is not NULL,
strnchrnul() never returns NULL pointer so in the change below,
'if (!fmt_end)' will be always false.

>
> Signed-off-by: Edward Adam Davis <eadavis@qq.com>
> ---
>   kernel/bpf/helpers.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
> index 449b9a5d3fe3..07490eba24fe 100644
> --- a/kernel/bpf/helpers.c
> +++ b/kernel/bpf/helpers.c
> @@ -826,7 +826,7 @@ int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
>   	u64 cur_arg;
>   	char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
>   
> -	fmt_end = strnchr(fmt, fmt_size, 0);
> +	fmt_end = strnchrnul(fmt, fmt_size, 0);
>   	if (!fmt_end)
>   		return -EINVAL;
>   	fmt_size = fmt_end - fmt;
Edward Adam Davis April 11, 2024, 11:05 a.m. UTC | #2 
> > The strnchr() is not suitable for obtaining the end of a string with a length
> > exceeding 1 and ending with a NUL character.
> 
> Could you give more detailed explanation with specific examples? I think
> strnchr() does the right thing here. Note that if fmt is not NULL,
> strnchrnul() never returns NULL pointer so in the change below,
> 'if (!fmt_end)' will be always false.
My mistake, strnchr() work well.
> 
> >
diff mbox series

Patch

diff --git a/kernel/bpf/helpers.c b/kernel/bpf/helpers.c
index 449b9a5d3fe3..07490eba24fe 100644
--- a/kernel/bpf/helpers.c
+++ b/kernel/bpf/helpers.c
@@ -826,7 +826,7 @@  int bpf_bprintf_prepare(char *fmt, u32 fmt_size, const u64 *raw_args,
 	u64 cur_arg;
 	char fmt_ptype, cur_ip[16], ip_spec[] = "%pXX";
 
-	fmt_end = strnchr(fmt, fmt_size, 0);
+	fmt_end = strnchrnul(fmt, fmt_size, 0);
 	if (!fmt_end)
 		return -EINVAL;
 	fmt_size = fmt_end - fmt;