[PATCH] vfs: fix statfs64() does not handle errors

[Li Wang]

statfs64() does NOT return -1 and setting errno to EOVERFLOW when some
variables(like: f_bsize) overflowed in the returned struct.

reproducer:
step1. mount hugetlbfs with two different pagesize on ppc64 arch.

$ hugeadm --pool-pages-max 16M:0
$ hugeadm --create-mount
$ mount | grep -i hugetlbfs
none on /var/lib/hugetlbfs/pagesize-16MB type hugetlbfs (rw,relatime,seclabel,pagesize=16777216)
none on /var/lib/hugetlbfs/pagesize-16GB type hugetlbfs (rw,relatime,seclabel,pagesize=17179869184)

step2. compile & run this C program.

$ cat statfs64_test.c

 #define _LARGEFILE64_SOURCE
 #include <stdio.h>
 #include <sys/statfs.h>

 int main()
 {
	struct statfs64 sb;
	int err;

	err = statfs64("/var/lib/hugetlbfs/pagesize-16GB", &sb);
	if (err)
		return -1;

	printf("sizeof f_bsize = %d, f_bsize=%ld\n", sizeof(sb.f_bsize), sb.f_bsize);

	return 0;
 }

$ gcc -m32 statfs64_test.c
$ ./a.out
sizeof f_bsize = 4, f_bsize=0

Signed-off-by: Li Wang <liwang@xxxxxxxxxx>
---

Notes:
    This is my first patch to kernel fs part, I'm not sure if
    this one useful, but just want someone have a look.
    
    thanks~

 fs/statfs.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/fs/statfs.c b/fs/statfs.c
index 083dc0a..849dde95 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -151,6 +151,23 @@ static int do_statfs64(struct kstatfs *st, struct statfs64 __user *p)
 	if (sizeof(buf) == sizeof(*st))
 		memcpy(&buf, st, sizeof(*st));
 	else {
+		if (sizeof buf.f_bsize == 4) {
+			if ((st->f_blocks | st->f_bfree | st->f_bavail |
+			     st->f_bsize | st->f_frsize) &
+			    0xffffffff00000000ULL)
+				return -EOVERFLOW;
+			/*
+			 * f_files and f_ffree may be -1; it's okay to stuff
+			 * that into 32 bits
+			 */
+			if (st->f_files != -1 &&
+			    (st->f_files & 0xffffffff00000000ULL))
+				return -EOVERFLOW;
+			if (st->f_ffree != -1 &&
+			    (st->f_ffree & 0xffffffff00000000ULL))
+				return -EOVERFLOW;
+		}
+
 		buf.f_type = st->f_type;
 		buf.f_bsize = st->f_bsize;
 		buf.f_blocks = st->f_blocks;
-- 
1.8.3.1