[PATCH 2/8] sysvshm: report error on failure to reattach, avoid crash

[Matt Helsley]

On Tue, Sep 14, 2010 at 03:02:04PM -0500, Nathan Lynch wrote:
> If ipcshm_restore fails to look up the file object for the region
> being restored, it should return the error to its caller and not
> proceed to dereference the file pointer.
> 
> Signed-off-by: Nathan Lynch <ntl at pobox.com>

(Important fix. Adding Oren to Cc)

Reviewed-by: Matt Helsley <matthltc at us.ibm.com>

> ---
>  ipc/shm.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/ipc/shm.c b/ipc/shm.c
> index eed4b9a..1ba9193 100644
> --- a/ipc/shm.c
> +++ b/ipc/shm.c
> @@ -334,7 +334,7 @@ int ipcshm_restore(struct ckpt_ctx *ctx, struct mm_struct *mm,
> 
>  	file = ckpt_obj_fetch(ctx, h->ino_objref, CKPT_OBJ_FILE);
>  	if (IS_ERR(file))
> -		PTR_ERR(file);
> +		return PTR_ERR(file);

Odd that the original code didn't trigger any unused result or must check
warnings. In linux/err.h I already see:

	static inline long __must_check PTR_ERR(const void *ptr)
	...

And in linux/compiler-gcc3.h
	if __GNUC_MINOR__ >= 4
	#define __must_check            __attribute__((warn_unused_result))
	#endif

or for those of us using GCC 4.x (linux/compiler-gcc4.h):
	#define __must_check            __attribute__((warn_unused_result))

and in my .config I have:
	CONFIG_SYSVIPC=y
	CONFIG_SYSVIPC_CHECKPOINT=y
	...
	CONFIG_ENABLE_MUST_CHECK=y

plus a simple test:

	#include <stdlib.h>

	static inline void * __attribute__((warn_unused_result)) foo(void)
	{
		return NULL;
	}

	int main (void)
	{
		if (0)
			foo();
		return 0;
	}

even without -Wall triggers the compiler warning just fine. So I can't
see why the warning is not triggering.

Cheers,
	-Matt