releases/4.19.34/vfs-fix-preadv64v2-and-pwritev64v2-compat-syscalls-w.patch

From bf9901d0c75ae562dcbbfebe290160e89f48d3c6 Mon Sep 17 00:00:00 2001
From: Aurelien Jarno <aurelien@aurel32.net>
Date: Thu, 6 Dec 2018 20:05:34 +0100
Subject: vfs: fix preadv64v2 and pwritev64v2 compat syscalls with offset == -1

[ Upstream commit cc4b1242d7e3b42eed73881fc749944146493e4f ]

The preadv2 and pwritev2 syscalls are supposed to emulate the readv and
writev syscalls when offset == -1. Therefore the compat code should
check for offset before calling do_compat_preadv64 and
do_compat_pwritev64. This is the case for the preadv2 and pwritev2
syscalls, but handling of offset == -1 is missing in their 64-bit
equivalent.

This patch fixes that, calling do_compat_readv and do_compat_writev when
offset == -1. This fixes the following glibc tests on x32:
 - misc/tst-preadvwritev2
 - misc/tst-preadvwritev64v2

Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: H.J. Lu <hjl.tools@gmail.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/read_write.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/read_write.c b/fs/read_write.c
index 8a2737f0d61d..562974a0616c 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1241,6 +1241,9 @@ COMPAT_SYSCALL_DEFINE5(preadv64v2, unsigned long, fd,
 		const struct compat_iovec __user *,vec,
 		unsigned long, vlen, loff_t, pos, rwf_t, flags)
 {
+	if (pos == -1)
+		return do_compat_readv(fd, vec, vlen, flags);
+
 	return do_compat_preadv64(fd, vec, vlen, pos, flags);
 }
 #endif
@@ -1347,6 +1350,9 @@ COMPAT_SYSCALL_DEFINE5(pwritev64v2, unsigned long, fd,
 		const struct compat_iovec __user *,vec,
 		unsigned long, vlen, loff_t, pos, rwf_t, flags)
 {
+	if (pos == -1)
+		return do_compat_writev(fd, vec, vlen, flags);
+
 	return do_compat_pwritev64(fd, vec, vlen, pos, flags);
 }
 #endif
-- 
2.19.1