linux-kernel - [PATCH] compat breakage in preadv() and pwritev()

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Message-ID: <20110313232446.GJ22723@ZenIV.linux.org.uk>
Date:	Sun, 13 Mar 2011 23:24:46 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH] compat breakage in preadv() and pwritev()

	Fix for a dumb preadv()/pwritev() compat bug - unlike the native
variants, compat_... ones forget to check FMODE_P{READ,WRITE}, so e.g.
on pipe the native preadv() will fail with -ESPIPE and compat one will
act as readv() and succeed.  Not critical, but it's a clear bug with trivial
fix, so IMO it's OK for -final.

Signed-off-by: Al Viro <viro@...iv.linux.org.uk>
---
 fs/compat.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/compat.c b/fs/compat.c
index f6fd0a0..691c3fd 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -1228,7 +1228,9 @@ compat_sys_preadv(unsigned long fd, const struct compat_iovec __user *vec,
 	file = fget_light(fd, &fput_needed);
 	if (!file)
 		return -EBADF;
-	ret = compat_readv(file, vec, vlen, &pos);
+	ret = -ESPIPE;
+	if (file->f_mode & FMODE_PREAD)
+		ret = compat_readv(file, vec, vlen, &pos);
 	fput_light(file, fput_needed);
 	return ret;
 }
@@ -1285,7 +1287,9 @@ compat_sys_pwritev(unsigned long fd, const struct compat_iovec __user *vec,
 	file = fget_light(fd, &fput_needed);
 	if (!file)
 		return -EBADF;
-	ret = compat_writev(file, vec, vlen, &pos);
+	ret = -ESPIPE;
+	if (file->f_mode & FMODE_PWRITE)
+		ret = compat_writev(file, vec, vlen, &pos);
 	fput_light(file, fput_needed);
 	return ret;
 }
--
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