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authorEric Biggers <ebiggers@google.com>2020-04-10 14:33:50 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2020-04-10 15:36:22 -0700
commit6e71582506258c9b2efd8f164706f2af2256cf16 (patch)
parent26c5d78c976ca298e59a56f6101a97b618ba3539 (diff)
docs: admin-guide: document the kernel.modprobe sysctl
Document the kernel.modprobe sysctl in the same place that all the other kernel.* sysctls are documented. Make sure to mention how to use this sysctl to completely disable module autoloading, and how this sysctl relates to CONFIG_STATIC_USERMODEHELPER. [ebiggers@google.com: v5] Link: http://lkml.kernel.org/r/20200318230515.171692-4-ebiggers@kernel.org Signed-off-by: Eric Biggers <ebiggers@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Cc: Alexei Starovoitov <ast@kernel.org> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Cc: Jeff Vander Stoep <jeffv@google.com> Cc: Jessica Yu <jeyu@kernel.org> Cc: Kees Cook <keescook@chromium.org> Cc: Luis Chamberlain <mcgrof@kernel.org> Cc: NeilBrown <neilb@suse.com> Link: http://lkml.kernel.org/r/20200312202552.241885-4-ebiggers@kernel.org Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 21 insertions, 0 deletions
diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index 335696d3360d..39c95c0e13d3 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -446,6 +446,27 @@ Notes:
successful IPC object allocation. If an IPC object allocation syscall
fails, it is undefined if the value remains unmodified or is reset to -1.
+The path to the usermode helper for autoloading kernel modules, by
+default "/sbin/modprobe". This binary is executed when the kernel
+requests a module. For example, if userspace passes an unknown
+filesystem type to mount(), then the kernel will automatically request
+the corresponding filesystem module by executing this usermode helper.
+This usermode helper should insert the needed module into the kernel.
+This sysctl only affects module autoloading. It has no effect on the
+ability to explicitly insert modules.
+If this sysctl is set to the empty string, then module autoloading is
+completely disabled. The kernel will not try to execute a usermode
+helper at all, nor will it call the kernel_module_request LSM hook.
+If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
+then the configured static usermode helper overrides this sysctl,
+except that the empty string is still accepted to completely disable
+module autoloading as described above.