Hi,
On 7/28/20 5:19 PM, Peilin Ye wrote:
> raw_cmd_copyout() is potentially copying uninitialized kernel stack memory
> since it is initializing `cmd` by assignment, which may cause the compiler
> to leave uninitialized holes in this structure. Fix it by using memcpy()
> instead.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 2145e15e0557 ("floppy: don't write kernel-only members to FDRAWCMD ioctl output")
> Suggested-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> Suggested-by: Arnd Bergmann <arnd@xxxxxxxx>
> Signed-off-by: Peilin Ye <yepeilin.cs@xxxxxxxxx>
Reviewed-by: Denis Efremov <efremov@xxxxxxxxx>
ptr comes from raw_cmd_copyin and it should be ok to use memcpy.
Jens, could you please take this one to your 5.9 branch?
> ---
> $ pahole -C "floppy_raw_cmd" drivers/block/floppy.o
> struct floppy_raw_cmd {
> unsigned int flags; /* 0 4 */
>
> /* XXX 4 bytes hole, try to pack */
>
> void * data; /* 8 8 */
> char * kernel_data; /* 16 8 */
> struct floppy_raw_cmd * next; /* 24 8 */
> long int length; /* 32 8 */
> long int phys_length; /* 40 8 */
> int buffer_length; /* 48 4 */
> unsigned char rate; /* 52 1 */
> unsigned char cmd_count; /* 53 1 */
> union {
> struct {
> unsigned char cmd[16]; /* 54 16 */
> /* --- cacheline 1 boundary (64 bytes) was 6 bytes ago --- */
> unsigned char reply_count; /* 70 1 */
> unsigned char reply[16]; /* 71 16 */
> }; /* 54 33 */
> unsigned char fullcmd[33]; /* 54 33 */
> }; /* 54 33 */
>
> /* XXX 1 byte hole, try to pack */
>
> /* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */
> int track; /* 88 4 */
> int resultcode; /* 92 4 */
> int reserved1; /* 96 4 */
> int reserved2; /* 100 4 */
>
> /* size: 104, cachelines: 2, members: 14 */
> /* sum members: 99, holes: 2, sum holes: 5 */
> /* last cacheline: 40 bytes */
> };
>
It would be nice to add lkml links with discussion on the issue or
https://www.nccgroup.com/us/about-us/newsroom-and-events/blog/2019/october/padding-the-struct-how-a-compiler-optimization-can-disclose-stack-memory/
in addition to pahole output.
> drivers/block/floppy.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/floppy.c b/drivers/block/floppy.c
> index 09079aee8dc4..b8ea98f7a9cb 100644
> --- a/drivers/block/floppy.c
> +++ b/drivers/block/floppy.c
> @@ -3126,7 +3126,9 @@ static int raw_cmd_copyout(int cmd, void __user *param,
> int ret;
>
> while (ptr) {
> - struct floppy_raw_cmd cmd = *ptr;
> + struct floppy_raw_cmd cmd;
> +
> + memcpy(&cmd, ptr, sizeof(cmd))> cmd.next = NULL;
> cmd.kernel_data = NULL;
> ret = copy_to_user(param, &cmd, sizeof(cmd));
>
Thanks,
Denis
