It is counterintuitive at best that mmap'ing a hugetlbfs file with
MAP_HUGETLB fails, while mmap'ing it without will a) succeed and b)
return huge pages.
Signed-off-by: Joern Engel <jo...@logfs.org>
---
mm/mmap.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/mm/mmap.c b/mm/mmap.c
index 2a594246..76eb6df 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -33,6 +33,7 @@
#include <linux/uprobes.h>
#include <linux/rbtree_augmented.h>
#include <linux/sched/sysctl.h>
+#include <linux/magic.h>
#include <asm/uaccess.h>
#include <asm/cacheflush.h>
@@ -1313,6 +1314,11 @@ unsigned long do_mmap_pgoff(struct file *file, unsigned
long addr,
return addr;
}
+static inline int is_hugetlb_file(struct file *file)
+{
+ return file->f_inode->i_sb->s_magic == HUGETLBFS_MAGIC;
+}
+
SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned long, len,
unsigned long, prot, unsigned long, flags,
unsigned long, fd, unsigned long, pgoff)
@@ -1322,11 +1328,12 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr,
unsigned long, len,
if (!(flags & MAP_ANONYMOUS)) {
audit_mmap_fd(fd, flags);
- if (unlikely(flags & MAP_HUGETLB))
- return -EINVAL;
file = fget(fd);
if (!file)
goto out;
+ retval = -EINVAL;
+ if (unlikely(flags & MAP_HUGETLB && !is_hugetlb_file(file)))
+ goto out_fput;
} else if (flags & MAP_HUGETLB) {
struct user_struct *user = NULL;
/*
@@ -1346,6 +1353,7 @@ SYSCALL_DEFINE6(mmap_pgoff, unsigned long, addr, unsigned
long, len,
flags &= ~(MAP_EXECUTABLE | MAP_DENYWRITE);
retval = vm_mmap_pgoff(file, addr, len, prot, flags, pgoff);
+out_fput:
if (file)
fput(file);
out:
--
1.7.10.4
--
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