On 25.08.22 11:50, Jan Beulich wrote:
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@xxxxxxxxxxxxxxx> Fixes: ab520be8cd5d ("xen/privcmd: Add IOCTL_PRIVCMD_DM_OP") Reported-by: Rustam Subkhankulov <subkhankulov@xxxxxxxxx> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx> 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)?
This would require to rework the loop in lock_pages() to be able to handle only a partial buffer. This would add some complexity, but OTOH I'd get an exact error code back in case of failure. I'll have a try and see how the result would look like. Juergen
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