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authorPeter Enderborg <peter.enderborg@sony.com>2020-07-16 09:15:11 +0200
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2020-07-23 17:10:25 +0200
commita24c6f7bc923d5e2f3139855eb09b0d480d6b410 (patch)
treef96b6939d66e6cb438690706dcb76b7e2a948f73
parent072e133d554bb74929f902582c8cf66d9fd12771 (diff)
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debugfs: Add access restriction option
Since debugfs include sensitive information it need to be treated carefully. But it also has many very useful debug functions for userspace. With this option we can have same configuration for system with need of debugfs and a way to turn it off. This gives a extra protection for exposure on systems where user-space services with system access are attacked. It is controlled by a configurable default value that can be override with a kernel command line parameter. (debugfs=) It can be on or off, but also internally on but not seen from user-space. This no-mount mode do not register a debugfs as filesystem, but client can register their parts in the internal structures. This data can be readed with a debugger or saved with a crashkernel. When it is off clients get EPERM error when accessing the functions for registering their components. Signed-off-by: Peter Enderborg <peter.enderborg@sony.com> Link: https://lore.kernel.org/r/20200716071511.26864-3-peter.enderborg@sony.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt15
-rw-r--r--fs/debugfs/inode.c39
-rw-r--r--fs/debugfs/internal.h14
-rw-r--r--lib/Kconfig.debug32
4 files changed, 100 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb95fad81c79..6766a308ad96 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -827,6 +827,21 @@
useful to also enable the page_owner functionality.
on: enable the feature
+ debugfs= [KNL] This parameter enables what is exposed to userspace
+ and debugfs internal clients.
+ Format: { on, no-mount, off }
+ on: All functions are enabled.
+ no-mount:
+ Filesystem is not registered but kernel clients can
+ access APIs and a crashkernel can be used to read
+ its content. There is nothing to mount.
+ off: Filesystem is not registered and clients
+ get a -EPERM as result when trying to register files
+ or directories within debugfs.
+ This is equivalent of the runtime functionality if
+ debugfs was not enabled in the kernel at all.
+ Default value is set in build-time with a kernel configuration.
+
debugpat [X86] Enable PAT debugging
decnet.addr= [HW,NET]
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index b7f2e971ecbc..2fcf66473436 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -35,6 +35,7 @@
static struct vfsmount *debugfs_mount;
static int debugfs_mount_count;
static bool debugfs_registered;
+static unsigned int debugfs_allow = DEFAULT_DEBUGFS_ALLOW_BITS;
/*
* Don't allow access attributes to be changed whilst the kernel is locked down
@@ -266,6 +267,9 @@ static struct dentry *debug_mount(struct file_system_type *fs_type,
int flags, const char *dev_name,
void *data)
{
+ if (!(debugfs_allow & DEBUGFS_ALLOW_API))
+ return ERR_PTR(-EPERM);
+
return mount_single(fs_type, flags, data, debug_fill_super);
}
@@ -311,6 +315,9 @@ static struct dentry *start_creating(const char *name, struct dentry *parent)
struct dentry *dentry;
int error;
+ if (!(debugfs_allow & DEBUGFS_ALLOW_API))
+ return ERR_PTR(-EPERM);
+
pr_debug("creating file '%s'\n", name);
if (IS_ERR(parent))
@@ -385,6 +392,11 @@ static struct dentry *__debugfs_create_file(const char *name, umode_t mode,
if (IS_ERR(dentry))
return dentry;
+ if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
+ failed_creating(dentry);
+ return ERR_PTR(-EPERM);
+ }
+
inode = debugfs_get_inode(dentry->d_sb);
if (unlikely(!inode)) {
pr_err("out of free dentries, can not create file '%s'\n",
@@ -541,6 +553,11 @@ struct dentry *debugfs_create_dir(const char *name, struct dentry *parent)
if (IS_ERR(dentry))
return dentry;
+ if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
+ failed_creating(dentry);
+ return ERR_PTR(-EPERM);
+ }
+
inode = debugfs_get_inode(dentry->d_sb);
if (unlikely(!inode)) {
pr_err("out of free dentries, can not create directory '%s'\n",
@@ -583,6 +600,11 @@ struct dentry *debugfs_create_automount(const char *name,
if (IS_ERR(dentry))
return dentry;
+ if (!(debugfs_allow & DEBUGFS_ALLOW_API)) {
+ failed_creating(dentry);
+ return ERR_PTR(-EPERM);
+ }
+
inode = debugfs_get_inode(dentry->d_sb);
if (unlikely(!inode)) {
pr_err("out of free dentries, can not create automount '%s'\n",
@@ -786,10 +808,27 @@ bool debugfs_initialized(void)
}
EXPORT_SYMBOL_GPL(debugfs_initialized);
+static int __init debugfs_kernel(char *str)
+{
+ if (str) {
+ if (!strcmp(str, "on"))
+ debugfs_allow = DEBUGFS_ALLOW_API | DEBUGFS_ALLOW_MOUNT;
+ else if (!strcmp(str, "no-mount"))
+ debugfs_allow = DEBUGFS_ALLOW_API;
+ else if (!strcmp(str, "off"))
+ debugfs_allow = 0;
+ }
+
+ return 0;
+}
+early_param("debugfs", debugfs_kernel);
static int __init debugfs_init(void)
{
int retval;
+ if (!(debugfs_allow & DEBUGFS_ALLOW_MOUNT))
+ return -EPERM;
+
retval = sysfs_create_mount_point(kernel_kobj, "debug");
if (retval)
return retval;
diff --git a/fs/debugfs/internal.h b/fs/debugfs/internal.h
index 034e6973cead..92af8ae31313 100644
--- a/fs/debugfs/internal.h
+++ b/fs/debugfs/internal.h
@@ -29,4 +29,18 @@ struct debugfs_fsdata {
*/
#define DEBUGFS_FSDATA_IS_REAL_FOPS_BIT BIT(0)
+/* Access BITS */
+#define DEBUGFS_ALLOW_API BIT(0)
+#define DEBUGFS_ALLOW_MOUNT BIT(1)
+
+#ifdef CONFIG_DEBUG_FS_ALLOW_ALL
+#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_MOUNT | DEBUGFS_ALLOW_API)
+#endif
+#ifdef CONFIG_DEBUG_FS_DISALLOW_MOUNT
+#define DEFAULT_DEBUGFS_ALLOW_BITS (DEBUGFS_ALLOW_API)
+#endif
+#ifdef CONFIG_DEBUG_FS_ALLOW_NONE
+#define DEFAULT_DEBUGFS_ALLOW_BITS (0)
+#endif
+
#endif /* _DEBUGFS_INTERNAL_H_ */
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 2bff6315224d..256e4ce65f1a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -476,6 +476,38 @@ config DEBUG_FS
If unsure, say N.
+choice
+ prompt "Debugfs default access"
+ depends on DEBUG_FS
+ default DEBUG_FS_ALLOW_ALL
+ help
+ This selects the default access restrictions for debugfs.
+ It can be overridden with kernel command line option
+ debugfs=[on,no-mount,off]. The restrictions apply for API access
+ and filesystem registration.
+
+config DEBUG_FS_ALLOW_ALL
+ bool "Access normal"
+ help
+ No restrictions apply. Both API and filesystem registration
+ is on. This is the normal default operation.
+
+config DEBUG_FS_DISALLOW_MOUNT
+ bool "Do not register debugfs as filesystem"
+ help
+ The API is open but filesystem is not loaded. Clients can still do
+ their work and read with debug tools that do not need
+ debugfs filesystem.
+
+config DEBUG_FS_ALLOW_NONE
+ bool "No access"
+ help
+ Access is off. Clients get -PERM when trying to create nodes in
+ debugfs tree and debugfs is not registered as a filesystem.
+ Client can then back-off or continue without debugfs access.
+
+endchoice
+
source "lib/Kconfig.kgdb"
source "lib/Kconfig.ubsan"