From 754efdc19b6195cd5e31419dba9590e6e2eb6139 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 14 Mar 2023 19:32:38 -0700 Subject: [PATCH] sched_getaffinity: don't assume 'cpumask_size()' is fully initialized [ Upstream commit 6015b1aca1a233379625385feb01dd014aca60b5 ] The getaffinity() system call uses 'cpumask_size()' to decide how big the CPU mask is - so far so good. It is indeed the allocation size of a cpumask. But the code also assumes that the whole allocation is initialized without actually doing so itself. That's wrong, because we might have fixed-size allocations (making copying and clearing more efficient), but not all of it is then necessarily used if 'nr_cpu_ids' is smaller. Having checked other users of 'cpumask_size()', they all seem to be ok, either using it purely for the allocation size, or explicitly zeroing the cpumask before using the size in bytes to copy it. See for example the ublk_ctrl_get_queue_affinity() function that uses the proper 'zalloc_cpumask_var()' to make sure that the whole mask is cleared, whether the storage is on the stack or if it was an external allocation. Fix this by just zeroing the allocation before using it. Do the same for the compat version of sched_getaffinity(), which had the same logic. Also, for consistency, make sched_getaffinity() use 'cpumask_bits()' to access the bits. For a cpumask_var_t, it ends up being a pointer to the same data either way, but it's just a good idea to treat it like you would a 'cpumask_t'. The compat case already did that. Reported-by: Ryan Roberts Link: https://lore.kernel.org/lkml/7d026744-6bd6-6827-0471-b5e8eae0be3f@arm.com/ Cc: Yury Norov Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- kernel/compat.c | 2 +- kernel/sched/core.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/kernel/compat.c b/kernel/compat.c index a2bc1d6ceb570..241516f326c04 100644 --- a/kernel/compat.c +++ b/kernel/compat.c @@ -240,7 +240,7 @@ COMPAT_SYSCALL_DEFINE3(sched_getaffinity, compat_pid_t, pid, unsigned int, len, if (len & (sizeof(compat_ulong_t)-1)) return -EINVAL; - if (!alloc_cpumask_var(&mask, GFP_KERNEL)) + if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) return -ENOMEM; ret = sched_getaffinity(pid, mask); diff --git a/kernel/sched/core.c b/kernel/sched/core.c index d5765b7c92f79..51ac62637e4ed 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -5661,14 +5661,14 @@ SYSCALL_DEFINE3(sched_getaffinity, pid_t, pid, unsigned int, len, if (len & (sizeof(unsigned long)-1)) return -EINVAL; - if (!alloc_cpumask_var(&mask, GFP_KERNEL)) + if (!zalloc_cpumask_var(&mask, GFP_KERNEL)) return -ENOMEM; ret = sched_getaffinity(pid, mask); if (ret == 0) { unsigned int retlen = min(len, cpumask_size()); - if (copy_to_user(user_mask_ptr, mask, retlen)) + if (copy_to_user(user_mask_ptr, cpumask_bits(mask), retlen)) ret = -EFAULT; else ret = retlen; -- 2.39.5