From a24c6f7bc923d5e2f3139855eb09b0d480d6b410 Mon Sep 17 00:00:00 2001 From: Peter Enderborg Date: Thu, 16 Jul 2020 09:15:11 +0200 Subject: 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 Link: https://lore.kernel.org/r/20200716071511.26864-3-peter.enderborg@sony.com Signed-off-by: Greg Kroah-Hartman --- fs/debugfs/inode.c | 39 +++++++++++++++++++++++++++++++++++++++ fs/debugfs/internal.h | 14 ++++++++++++++ 2 files changed, 53 insertions(+) (limited to 'fs/debugfs') 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_ */ -- cgit v1.2.3