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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Alexander Viro <viro@zeniv.linux.org.uk>,
        "H.J. Lu" <hjl.tools@gmail.com>,
        Aurelien Jarno <aurelien@aurel32.net>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 093/187] vfs: fix preadv64v2 and pwritev64v2 compat syscalls with offset == -1
Date:   Thu,  4 Apr 2019 10:47:10 +0200
Message-Id: <20190404084607.528446133@linuxfoundation.org>
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4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ 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