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Date: Tue, 6 Jan 2009 10:12:38 -0500
From: Robin Getz <rgetz@...ckfin.uclinux.org>
To: "Greg KH" <gregkh@...e.de>
Cc: "Mike Frysinger" <vapier.adi@...il.com>, viro@...iv.linux.org.uk,
linux-kernel@...r.kernel.org
Subject: Re: debugfs & vfs file permission issue?
On Tue 6 Jan 2009 07:05, Robin Getz suggested:
>
> adding a readonly, and writeonly, and ensuring that when you call
> debugfs_create_*, the mode is checked, and the "correct" fops are set
> doesn't seem like it would be a bad idea? This would enforce the
> kernel programmer's view on the world, and not allow pesky root users
> to override things....
>
> Greg - would you take something like that?
How about this?
Feel free to nak it - we can do the same thing where we are calling the
debugfs_create_* functions - this just makes it cleaner in my opinion.
---
In many SOC implementations there are hardware registers can be read only,
or write only. This extends the debugfs to enforce the file permissions for
these types of registers, by providing a set of fops which are read only
or write only. This assumes that the kernel developer knows more about the
hardware than the user (even root users) - which is normally true.
Signed-off-by: Robin Getz <rgetz@...ckfin.uclinux.org>
---
This fixes things, which use to crash (SPORT1_TX is a write only hardware
register).
root:/sys/kernel/debug/blackfin/SPORT> ls -l SPORT1_TX
--w------- 1 root root 0 Jan 1 2007 SPORT1_TX
root:/sys/kernel/debug/blackfin/SPORT> cat SPORT1_TX
cat: read error: Permission denied
root:/sys/kernel/debug/blackfin/SPORT> chmod +r SPORT1_TX
root:/sys/kernel/debug/blackfin/SPORT> ls -l SPORT1_TX
-rw-r--r-- 1 root root 0 Jan 1 2007 SPORT1_TX
root:/sys/kernel/debug/blackfin/SPORT> cat SPORT1_TX
cat: read error: Permission denied
Without this patch, things crash - but as Greg suggested - the same thing can
be done other places.
fs/debugfs/file.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 63 insertions(+)
Index: fs/debugfs/file.c
===================================================================
--- fs/debugfs/file.c (revision 5943)
+++ fs/debugfs/file.c (working copy)
@@ -67,6 +67,8 @@
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(fops_u8, debugfs_u8_get, debugfs_u8_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u8_ro, debugfs_u8_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u8_wo, NULL, debugfs_u8_set, "%llu\n");
/**
* debugfs_create_u8 - create a debugfs file that is used to read and write an unsigned 8-bit value
@@ -95,6 +97,13 @@
struct dentry *debugfs_create_u8(const char *name, mode_t mode,
struct dentry *parent, u8 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u8_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u8_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_u8);
}
EXPORT_SYMBOL_GPL(debugfs_create_u8);
@@ -110,6 +119,8 @@
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(fops_u16, debugfs_u16_get, debugfs_u16_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u16_ro, debugfs_u16_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u16_wo, NULL, debugfs_u16_set, "%llu\n");
/**
* debugfs_create_u16 - create a debugfs file that is used to read and write an unsigned 16-bit value
@@ -138,6 +149,13 @@
struct dentry *debugfs_create_u16(const char *name, mode_t mode,
struct dentry *parent, u16 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u16_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u16_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_u16);
}
EXPORT_SYMBOL_GPL(debugfs_create_u16);
@@ -153,6 +171,8 @@
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(fops_u32, debugfs_u32_get, debugfs_u32_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u32_ro, debugfs_u32_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u32_wo, NULL, debugfs_u32_set, "%llu\n");
/**
* debugfs_create_u32 - create a debugfs file that is used to read and write an unsigned 32-bit value
@@ -181,6 +201,13 @@
struct dentry *debugfs_create_u32(const char *name, mode_t mode,
struct dentry *parent, u32 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u32_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u32_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_u32);
}
EXPORT_SYMBOL_GPL(debugfs_create_u32);
@@ -197,6 +224,8 @@
return 0;
}
DEFINE_SIMPLE_ATTRIBUTE(fops_u64, debugfs_u64_get, debugfs_u64_set, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u64_ro, debugfs_u64_get, NULL, "%llu\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_u64_wo, NULL, debugfs_u64_set, "%llu\n");
/**
* debugfs_create_u64 - create a debugfs file that is used to read and write an unsigned 64-bit value
@@ -225,15 +254,28 @@
struct dentry *debugfs_create_u64(const char *name, mode_t mode,
struct dentry *parent, u64 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u64_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_u64_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_u64);
}
EXPORT_SYMBOL_GPL(debugfs_create_u64);
DEFINE_SIMPLE_ATTRIBUTE(fops_x8, debugfs_u8_get, debugfs_u8_set, "0x%02llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x8_ro, debugfs_u8_get, NULL, "0x%02llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x8_wo, NULL, debugfs_u8_set, "0x%02llx\n");
DEFINE_SIMPLE_ATTRIBUTE(fops_x16, debugfs_u16_get, debugfs_u16_set, "0x%04llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x16_ro, debugfs_u16_get, NULL, "0x%04llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x16_wo, NULL, debugfs_u16_set, "0x%04llx\n");
DEFINE_SIMPLE_ATTRIBUTE(fops_x32, debugfs_u32_get, debugfs_u32_set, "0x%08llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x32_ro, debugfs_u32_get, NULL, "0x%08llx\n");
+DEFINE_SIMPLE_ATTRIBUTE(fops_x32_wo, NULL, debugfs_u32_set, "0x%08llx\n");
/*
* debugfs_create_x{8,16,32} - create a debugfs file that is used to read and write an unsigned {8,16,32}-bit value
@@ -256,6 +298,13 @@
struct dentry *debugfs_create_x8(const char *name, mode_t mode,
struct dentry *parent, u8 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x8_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x8_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_x8);
}
EXPORT_SYMBOL_GPL(debugfs_create_x8);
@@ -273,6 +322,13 @@
struct dentry *debugfs_create_x16(const char *name, mode_t mode,
struct dentry *parent, u16 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x16_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x16_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_x16);
}
EXPORT_SYMBOL_GPL(debugfs_create_x16);
@@ -290,6 +346,13 @@
struct dentry *debugfs_create_x32(const char *name, mode_t mode,
struct dentry *parent, u32 *value)
{
+ /*if there are no write bits set make read only */
+ if (!(mode & S_IWUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x32_ro);
+ /* if there are no read bits set, make write only */
+ if (!(mode & S_IRUGO))
+ return debugfs_create_file(name, mode, parent, value, &fops_x32_wo);
+
return debugfs_create_file(name, mode, parent, value, &fops_x32);
}
EXPORT_SYMBOL_GPL(debugfs_create_x32);
--
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