On 25.08.2022 11:26, Juergen Gross wrote:
The error exit of privcmd_ioctl_dm_op() is calling unlock_pages() potentially with pages being NULL, leading to a NULL dereference.
Additionally lock_pages() doesn't check for pin_user_pages_fast() having been completely successful, resulting in potentially not locking all pages into memory. This could result in sporadic failures when using the related memory in user mode.
Fix all of that by calling unlock_pages() always with the real number of pinned pages, which will be zero in case pages being NULL, and by checking the number of patches pinned by pin_user_pages_fast()
Nit: s/patches/pages/
matching the expected number of pages.
Cc: stable@vger.kernel.org Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP") Reported-by: Rustam Subkhankulov subkhankulov@ispras.ru Signed-off-by: Juergen Gross jgross@suse.com
Reviewed-by: Jan Beulich jbeulich@suse.com
I have a question / suggestion, though:
--- a/drivers/xen/privcmd.c +++ b/drivers/xen/privcmd.c @@ -602,6 +602,10 @@ static int lock_pages( *pinned += page_count; nr_pages -= page_count; pages += page_count;
/* Exact reason isn't known, EFAULT is one possibility. */if (page_count < requested)return -EFAULT;
I don't really know the inner workings of pin_user_pages_fast() nor what future plans there are with it. To be as independent of its behavior as possible, how about bailing here only when page_count actually is zero (i.e. no forward progress)?
Jan