PaX/GrSecurity patched kernels implement a dialect of C that relies on a
GCC plugin for enforcement. A basic idea in this dialect is that
function pointers in structures should not change during runtime.
This causes code that modifies function pointers at runtime to fail to
compile in many instances. The autotools checks rely on whether or
not small test cases compile against a given kernel. Some
autotools checks assume some default case if other cases fail. When one
of these autotools checks tests a PaX/GrSecurity patched kernel by
modifying a function pointer at runtime, the default case will be used.
Early detection of such situations is possible by relying on compiler
warnings, which are compiler errors when --enable-debug is used.
Unfortunately, very few people build ZFS with --enable-debug. The more
common situation is that these issues manifest themselves as runtime
failures in the form of NULL pointer exceptions.
Previous patches that addressed such issues with PaX/GrSecurity
compatibility largely relied on rewriting autotools checks to avoid
runtime function pointer modification or the addition of PaX/GrSecurity
specific checks. This patch takes the previous work to its logical
conclusion by eliminating the use of runtime function pointer
modification. This permits the removal of PaX-specific autotools checks
in favor of ones that work across all supported kernels.
This should resolve issues that were reported to occur with
PaX/GrSecurity-patched Linux 3.7.5 kernels on Gentoo Linux.
https://bugs.gentoo.org/show_bug.cgi?id=457176
We should be able to prevent future regressions in PaX/GrSecurity
compatibility by ensuring that all changes to ZFSOnLinux avoid runtime
function pointer modification. At the same time, this does not solve the
issue of silent failures triggering default cases in the autotools
check, which is what permitted these regressions to become runtime
failures in the first place. This will need to be addressed in a future
patch.
Reported-by: Marcin Mirosław <bug@mejor.pl>
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#1300
Gentoo Hardened kernels include the PaX/GRSecurity patches. They use a
dialect of C that relies on a GCC plugin. In particular, struct
file_operations has been marked do_const in the PaX/GRSecurity dialect,
which causes GCC to consider all instances of it as const. This caused
failures in the autotools checks and the ZFS source code.
To address this, we modify the autotools checks to take into account
differences between the PaX C dialect and the regular C dialect. We also
modify struct zfs_acl's z_ops member to be a pointer to a function
pointer table. Lastly, we modify zpl_put_link() to address a PaX change
to the function prototype of nd_get_link(). This avoids compiler errors
in the PaX/GRSecurity dialect.
Note that the change in zpl_put_link() causes a warning that becomes a
build failure when debugging is enabled. Fixing that warning requires
ryao/spl@5ca50ef459.
Signed-off-by: Richard Yao <ryao@cs.stonybrook.edu>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#484
The Linux 3.1 kernel updated the fops->fsync() callback yet again.
They now pass the requested range and delegate the responsibility
for calling filemap_write_and_wait_range() to the callback. In
addition imutex is no longer held by the caller and the callback
is responsible for taking the lock if required.
This commit updates the code to provide a zpl_fsync() function
for the updated API. Implementations for the previous two APIs
are also maintained for compatibility.
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes#445
Newer versions of gcc are getting smart enough to detect the sloppy
syntax used for the autoconf tests. It is now generating warnings
for unused/undeclared variables. Newer version of gcc even have
the -Wunused-but-set-variable option set by default. This isn't a
problem except when -Werror is set and they get promoted to an error.
In this case the autoconf test will return an incorrect result which
will result in a build failure latter on.
To handle this I'm tightening up many of the autoconf tests to
explicitly mark variables as unused to suppress the gcc warning.
Remember, all of the autoconf code can never actually be run we
just want to get a clean build error to detect which APIs are
available. Never using a variable is absolutely fine for this.
Closes#176
The fsync() callback in the file_operations structure used to take
3 arguments. The callback now only takes 2 arguments because the
dentry argument was determined to be unused by all consumers. To
handle this a compatibility prototype was added to ensure the right
prototype is used. Our implementation never used the dentry argument
either so it's just a matter of using the right prototype.
Richard Yao
Brian Behlendorf