2024-02-02 12:43:49

by Arnd Bergmann

Subject: [PATCH] mm/damon/dbgfs: fix bogus string length

From: Arnd Bergmann <[email protected]>

gcc correctly points out that using strnlen() on a fixed size array
is nonsense with an overlong limit:

mm/damon/dbgfs.c: In function 'damon_dbgfs_deprecated_read':
mm/damon/dbgfs.c:814:19: error: 'strnlen' specified bound 1024 exceeds source size 512 [-Werror=stringop-overread]
814 | int len = strnlen(kbuf, 1024);
| ^~~~~~~~~~~~~~~~~~~
mm/damon/dbgfs.c:813:14: note: source object allocated here
813 | char kbuf[512] = DAMON_DBGFS_DEPRECATION_NOTICE;
| ^~~~

In fact, neither of the arbitrary limits are needed here: The first
one can just be a static const string and avoid wasting any more
space then necessary, and the strnlen() can be either strlen() or
sizeof(kbuf)-1, both of which the compiler turns into the same
constant here.

Fixes: adf9047adfff ("mm/damon/dbgfs: implement deprecation notice file")
Signed-off-by: Arnd Bergmann <[email protected]>
---
mm/damon/dbgfs.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/mm/damon/dbgfs.c b/mm/damon/dbgfs.c
index f7abbc0633aa..4a189eb65d14 100644
--- a/mm/damon/dbgfs.c
+++ b/mm/damon/dbgfs.c
@@ -810,10 +810,9 @@ static void dbgfs_destroy_ctx(struct damon_ctx *ctx)
static ssize_t damon_dbgfs_deprecated_read(struct file *file,
char __user *buf, size_t count, loff_t *ppos)
{
- char kbuf[512] = DAMON_DBGFS_DEPRECATION_NOTICE;
- int len = strnlen(kbuf, 1024);
+ static const char kbuf[] = DAMON_DBGFS_DEPRECATION_NOTICE;

- return simple_read_from_buffer(buf, count, ppos, kbuf, len);
+ return simple_read_from_buffer(buf, count, ppos, kbuf, strlen(kbuf));
}

/*
--
2.39.2

2024-02-02 17:17:53

by SeongJae Park

Subject: Re: [PATCH] mm/damon/dbgfs: fix bogus string length

Hi Arnd,

On Fri, 2 Feb 2024 13:43:26 +0100 Arnd Bergmann <[email protected]> wrote:

> From: Arnd Bergmann <[email protected]>
>
> gcc correctly points out that using strnlen() on a fixed size array
> is nonsense with an overlong limit:
>
> mm/damon/dbgfs.c: In function 'damon_dbgfs_deprecated_read':
> mm/damon/dbgfs.c:814:19: error: 'strnlen' specified bound 1024 exceeds source size 512 [-Werror=stringop-overread]
> 814 | int len = strnlen(kbuf, 1024);
> | ^~~~~~~~~~~~~~~~~~~
> mm/damon/dbgfs.c:813:14: note: source object allocated here
> 813 | char kbuf[512] = DAMON_DBGFS_DEPRECATION_NOTICE;
> | ^~~~
>
> In fact, neither of the arbitrary limits are needed here: The first
> one can just be a static const string and avoid wasting any more
> space then necessary, and the strnlen() can be either strlen() or
> sizeof(kbuf)-1, both of which the compiler turns into the same
> constant here.

Thank you for this fix!

>
> Fixes: adf9047adfff ("mm/damon/dbgfs: implement deprecation notice file")
> Signed-off-by: Arnd Bergmann <[email protected]>

Reviewed-by: SeongJae Park <[email protected]>


Thanks,
SJ

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