linux-kernel - [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for 64-bit f

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Date:   Thu,  5 Oct 2017 21:36:36 +0300
From:   Sergey Klyaus <sergey.m.klyaus@...il.com>
To:     sergey.m.klyaus@...il.com
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH] vfs: fix statfs64() returning impossible EOVERFLOW for 64-bit f_files

compat_statfs64 structure has some 32-bit and some 64-bit fields, so
64d2ab32e "vfs: fix put_compat_statfs64() does not handle errors" fixed
32-bit overflow checks not being performed, but accidentally enabled
checks for f_files and f_ffree that are 64-bit and cannot have overflow.
Now checks for both groups of fields are enabled by different
conditions.

This broke my Steam runtime and can be reproduced with this test case:

    # mount -t tmpfs -o nr_inodes=4294967297 tmpfs /mnt
    $ cat statfs.c

int main() {
        struct statvfs sv;
        statvfs("/mnt", &sv);
        printf("%d %llu %llu\n", errno,
                (unsigned long long) sv.f_files,
                (unsigned long long) sv.f_ffree);
        return 0;
}
    $ gcc -g -m32 -D_FILE_OFFSET_BITS=64 statfs.c
    $ ./a.out
    75 134513445 0
    |  \- some junk on stack
    EOVERFLOW

Signed-off-by: Sergey Klyaus <sergey.m.klyaus@...il.com>
---
 fs/statfs.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/statfs.c b/fs/statfs.c
index fab9b6a3c116..073bb2d1871e 100644
--- a/fs/statfs.c
+++ b/fs/statfs.c
@@ -307,6 +307,8 @@ static int put_compat_statfs64(struct compat_statfs64 __user *ubuf, struct kstat
 		if ((kbuf->f_type | kbuf->f_bsize | kbuf->f_namelen |
 		     kbuf->f_frsize | kbuf->f_flags) & 0xffffffff00000000ULL)
 			return -EOVERFLOW;
+	}
+	if (sizeof(ubuf->f_blocks) == 4) {
 		/* f_files and f_ffree may be -1; it's okay
 		 * to stuff that into 32 bits */
 		if (kbuf->f_files != 0xffffffffffffffffULL
-- 
2.14.1