numa: change get_mempolicy() to use nr_node_ids instead of MAX_NUMNODES

Ralph Campbell · torvalds · commit 050c17f239fd · 2019-02-21T09:00:59.000-08:00
The system call, get_mempolicy() [1], passes an unsigned long *nodemask pointer and an unsigned long maxnode argument which specifies the length of the user's nodemask array in bits (which is rounded up). The manual page says that if the maxnode value is too small, get_mempolicy will return EINVAL but there is no system call to return this minimum value. To determine this value, some programs search /proc/<pid>/status for a line starting with "Mems_allowed:" and use the number of digits in the mask to determine the minimum value. A recent change to the way this line is formatted [2] causes these programs to compute a value less than MAX_NUMNODES so get_mempolicy() returns EINVAL. Change get_mempolicy(), the older compat version of get_mempolicy(), and the copy_nodes_to_user() function to use nr_node_ids instead of MAX_NUMNODES, thus preserving the defacto method of computing the minimum size for the nodemask array and the maxnode argument. [1] http://man7.org/linux/man-pages/man2/get_mempolicy.2.html [2] https://lore.kernel.org/lkml/1545405631-6808-1-git-send-email-longman@redhat.com Link: http://lkml.kernel.org/r/20190211180245.22295-1-rcampbell@nvidia.com Fixes: 4fb8e5b ("include/linux/nodemask.h: use nr_node_ids (not MAX_NUMNODES) in __nodemask_pr_numnodes()") Signed-off-by: Ralph Campbell <rcampbell@nvidia.com> Suggested-by: Alexander Duyck <alexander.duyck@gmail.com> Cc: Waiman Long <longman@redhat.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
@@ -1314,7 +1314,7 @@ static int copy_nodes_to_user(unsigned long __user *mask, unsigned long maxnode,
 			      nodemask_t *nodes)
 {
 	unsigned long copy = ALIGN(maxnode-1, 64) / 8;
-	const int nbytes = BITS_TO_LONGS(MAX_NUMNODES) * sizeof(long);
+	unsigned int nbytes = BITS_TO_LONGS(nr_node_ids) * sizeof(long);
 
 	if (copy > nbytes) {
 		if (copy > PAGE_SIZE)
@@ -1491,7 +1491,7 @@ static int kernel_get_mempolicy(int __user *policy,
 	int uninitialized_var(pval);
 	nodemask_t nodes;
 
-	if (nmask != NULL && maxnode < MAX_NUMNODES)
+	if (nmask != NULL && maxnode < nr_node_ids)
 		return -EINVAL;
 
 	err = do_get_mempolicy(&pval, &nodes, addr, flags);
@@ -1527,7 +1527,7 @@ COMPAT_SYSCALL_DEFINE5(get_mempolicy, int __user *, policy,
 	unsigned long nr_bits, alloc_size;
 	DECLARE_BITMAP(bm, MAX_NUMNODES);
 
-	nr_bits = min_t(unsigned long, maxnode-1, MAX_NUMNODES);
+	nr_bits = min_t(unsigned long, maxnode-1, nr_node_ids);
 	alloc_size = ALIGN(nr_bits, BITS_PER_LONG) / 8;
 
 	if (nmask)
