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A previous patch fixed the "create-unlink-getattr" idiom: if getattr is
called on an unlinked file, we try to find an open fid attached to the
corresponding inode.
We have a similar issue with file permissions and setattr:
open("./test.txt", O_RDWR|O_CREAT, 0666) = 4
chmod("./test.txt", 0) = 0
truncate("./test.txt", 0) = -1 EACCES (Permission denied)
ftruncate(4, 0) = -1 EACCES (Permission denied)
The failure is expected with truncate() but not with ftruncate().
This happens because the lookup code does find a matching fid in the
dentry list. Unfortunately, this is not an open fid and the server
will be forced to rely on the path name, rather than on an open file
descriptor. This is the case in QEMU: the setattr operation will use
truncate() and fail because of bad write permissions.
This patch changes the logic in the lookup code, so that we consider
open fids first. It gives a chance to the server to match this open
fid to an open file descriptor and use ftruncate() instead of truncate().
This does not change the current behaviour for truncate() and other
path name based syscalls, since file permissions are checked earlier
in the VFS layer.
With this patch, we get:
open("./test.txt", O_RDWR|O_CREAT, 0666) = 4
chmod("./test.txt", 0) = 0
truncate("./test.txt", 0) = -1 EACCES (Permission denied)
ftruncate(4, 0) = 0
Link: http://lkml.kernel.org/r/20200923141146.90046-4-jianyong.wu@arm.com
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
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| kernel | ||
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| README | ||
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.