When FORTIFY_SOURCE reports about a run-time buffer overread, the wrong
buffer size was being shown in the error message. (The bounds checking
was correct.)

Fixes: 3d965b33e40d ("fortify: Improve buffer overflow reporting")
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: <linux-hardening@vger.kernel.org>
---
 include/linux/fortify-string.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index e4ce1cae03bf..b3b53f8c1b28 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -596,7 +596,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
 	if (p_size != SIZE_MAX && p_size < size)
 		fortify_panic(func, FORTIFY_WRITE, p_size, size, true);
 	else if (q_size != SIZE_MAX && q_size < size)
-		fortify_panic(func, FORTIFY_READ, p_size, size, true);
+		fortify_panic(func, FORTIFY_READ, q_size, size, true);
 
 	/*
 	 * Warn when writing beyond destination field size.
-- 
2.34.1

On 29/07/25 17:18, Kees Cook wrote:
> When FORTIFY_SOURCE reports about a run-time buffer overread, the wrong
> buffer size was being shown in the error message. (The bounds checking
> was correct.)
> 
> Fixes: 3d965b33e40d ("fortify: Improve buffer overflow reporting")
> Signed-off-by: Kees Cook <kees@kernel.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Thanks!
-Gustavo

> ---
> Cc: <linux-hardening@vger.kernel.org>
> ---
>   include/linux/fortify-string.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
> index e4ce1cae03bf..b3b53f8c1b28 100644
> --- a/include/linux/fortify-string.h
> +++ b/include/linux/fortify-string.h
> @@ -596,7 +596,7 @@ __FORTIFY_INLINE bool fortify_memcpy_chk(__kernel_size_t size,
>   	if (p_size != SIZE_MAX && p_size < size)
>   		fortify_panic(func, FORTIFY_WRITE, p_size, size, true);
>   	else if (q_size != SIZE_MAX && q_size < size)
> -		fortify_panic(func, FORTIFY_READ, p_size, size, true);
> +		fortify_panic(func, FORTIFY_READ, q_size, size, true);
>   
>   	/*
>   	 * Warn when writing beyond destination field size.