[patch] vfs: check for integer overflows in posix_acl_alloc()

[Dan Carpenter <dan.carpenter@oracle.com>]

We've seen cases where people passed negative numbers to
posix_acl_alloc() and we fixed the caller.  For example 093019cf1b "xfs:
fix acl count validation in xfs_acl_from_disk()".  But there are other
places which might be affected like ext4_acl_from_disk() which checks
for negative but doesn't check an upper limit.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index cea4623..cd7fd2f 100644
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -46,7 +46,12 @@ posix_acl_alloc(int count, gfp_t flags)
 {
 	const size_t size = sizeof(struct posix_acl) +
 	                    count * sizeof(struct posix_acl_entry);
-	struct posix_acl *acl = kmalloc(size, flags);
+	struct posix_acl *acl;
+
+	if (count < 0 || count > (SIZE_MAX - sizeof(struct posix_acl) /
+					sizeof(struct posix_acl_entry)))
+		return NULL;
+	acl = kmalloc(size, flags);
 	if (acl)
 		posix_acl_init(acl, count);
 	return acl;