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    Subject[PATCH 4.9 37/50] vfs: check fd has read access in kernel_read_file_from_fd()
    Date
    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
    @@ -994,7 +994,7 @@ 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);

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