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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,
        "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        Hao Sun <sunhao.th@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>
Subject: [PATCH 4.19 18/37] vfs: check fd has read access in kernel_read_file_from_fd()
Date:   Mon, 25 Oct 2021 21:14:43 +0200
Message-Id: <20211025190931.974851341@linuxfoundation.org>
In-Reply-To: <20211025190926.680827862@linuxfoundation.org>
References: <20211025190926.680827862@linuxfoundation.org>
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From: Matthew Wilcox (Oracle) <willy@infradead.org>

commit 032146cda85566abcd1c4884d9d23e4e30a07e9a upstream.

If we open a file without read access and then pass the fd to a syscall
whose implementation calls kernel_read_file_from_fd(), we get a warning
from __kernel_read():

        if (WARN_ON_ONCE(!(file->f_mode & FMODE_READ)))

This currently affects both finit_module() and kexec_file_load(), but it
could affect other syscalls in the future.

Link: https://lkml.kernel.org/r/20211007220110.600005-1-willy@infradead.org
Fixes: b844f0ecbc56 ("vfs: define kernel_copy_file_from_fd()")
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reported-by: Hao Sun <sunhao.th@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Mimi Zohar <zohar@linux.ibm.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 fs/exec.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/exec.c
+++ b/fs/exec.c
@@ -984,7 +984,7 @@ int kernel_read_file_from_fd(int fd, voi
 	struct fd f = fdget(fd);
 	int ret = -EBADF;
 
-	if (!f.file)
+	if (!f.file || !(f.file->f_mode & FMODE_READ))
 		goto out;
 
 	ret = kernel_read_file(f.file, buf, size, max_size, id);