From 40a2159abf3d0107bba359246554bd7d56f2171b Mon Sep 17 00:00:00 2001 From: Ben Hutchings Date: Mon, 28 Apr 2008 15:59:58 +0100 Subject: [PATCH] sysfs: Disallow truncation of files in sysfs sysfs allows attribute files to be truncated, e.g. using ftruncate(), with the expected effect on their inode. For most attributes, this doesn't change the "real" size of the file i.e. how much can be read from it. However, the parameter validation for reading and writing binary attribute files is based on the inode size and not the size specified in the file's bin_attribute, so it can be broken by this. For example, if we try using dd to write to such a file: # pwd /sys/bus/pci/devices/0000:08:00.0 # ls -l config -rw-r--r-- 1 root root 4096 Feb 1 17:35 config # dd if=/dev/zero of=config bs=4 count=1 1+0 records in 1+0 records out # ls -l config -rw-r--r-- 1 root root 0 Feb 1 17:50 config # dd if=/dev/zero of=config bs=4 count=1 seek=128 dd: writing `config': No space left on device 1+0 records in 0+0 records out Also, after truncation to 0, parameter validation for read and write is disabled. Most bin_attribute read and write methods also validate the size and offset, but for some this will allow out-of-range access. This may be a security issue, though access to such files is often limited to root. In any case, the validation should remain for safety's sake!) This was previously reported in Bugzilla as bug 9867. sysfs should ignore size changes or else refuse them (by returning -EINVAL). This patch makes it ignore them. Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- fs/sysfs/inode.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/fs/sysfs/inode.c b/fs/sysfs/inode.c index f8b82e7..eb53c63 100644 --- a/fs/sysfs/inode.c +++ b/fs/sysfs/inode.c @@ -59,6 +59,8 @@ int sysfs_setattr(struct dentry * dentry, struct iattr * iattr) if (error) return error; + iattr->ia_valid &= ~ATTR_SIZE; /* ignore size changes */ + error = inode_setattr(inode, iattr); if (error) return error; -- 2.7.4