2de203d8ab
Some interface files in debugfs support the read method
dfs_file_read(), but their rwx permissions is shown as
unreadable.
In the user mode, the following problem can be clearly seen:
# ls -l /sys/kernel/debug/ubi/ubi0/
total 0
--w------- 1 root root 0 Oct 22 16:26 chk_fastmap
--w------- 1 root root 0 Oct 22 16:26 chk_gen
--w------- 1 root root 0 Oct 22 16:26 chk_io
-r-------- 1 root root 0 Oct 22 16:26 detailed_erase_block_info
--w------- 1 root root 0 Oct 22 16:26 tst_disable_bgt
--w------- 1 root root 0 Oct 22 16:26 tst_emulate_bitflips
--w------- 1 root root 0 Oct 22 16:26 tst_emulate_io_failures
--w------- 1 root root 0 Oct 22 16:26 tst_emulate_power_cut
--w------- 1 root root 0 Oct 22 16:26 tst_emulate_power_cut_max
--w------- 1 root root 0 Oct 22 16:26 tst_emulate_power_cut_min
It shows that these files do not have read permission 'r',
but we can actually read their contents.
# echo 1 > /sys/kernel/debug/ubi/ubi0/chk_io
# cat /sys/kernel/debug/ubi/ubi0/chk_io
1
User's permission access is determined by capabilities.
Of course, the root user is not restricted from reading
these files.
When reading a debugfs file, the process is as follows:
ksys_read()
vfs_read()
if (file->f_op->read)
file->f_op->read()
full_proxy_open()
real_fops->read()
dfs_file_read() -- Read method of debugfs file.
else if (file->f_op->read_iter)
new_sync_read()
else
ret = -EINVAL -- Return -EINVAL if no read method.
This indicates that the debugfs file can be read as long as the read
method of the debugfs file is registered. This patch adds the read
permission display for file that support the read method.
Signed-off-by: ZhaoLong Wang <wangzhaolong1@huawei.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.