Messages in this thread | | | Subject | Re: [PATCH] fs: Add flags to __d_path for suppressing suffix andmapping /proc/self | From | Tetsuo Handa <> | Date | Tue, 16 Feb 2010 21:11:44 +0900 |
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Al Viro wrote: > > Also, procfs is usually mounted on /proc , but it can be mounted on /proc2 , > > /mnt/proc3 or /p . Thus, the caller of __d_path() can't convert /proc/PID to > > /proc/self from string returned by __d_path() because the caller can't find > > the mount point of procfs from the returned string. If the caller traverses > > dentry/vfsmount tree in order to find the mount point of procfs, it results in > > duplicating __d_path() because the the caller does not use __d_path(). > > No. If you don't care which instance it is, you can bloody well check that > superblock is that of a procfs and track the path to its root *in* *caller*.
I couldn't catch. Are you suggesting that TOMOYO should not call __d_path() for dentry if dentry->d_sb->s_magic == PROC_SUPER_MAGIC ?
> Instead of calling d_path and looking at vfsmount tree at all. And you'd > better do that without assumptions that no name in procfs could be a number > unrelated to PIDs (i.e. you'd need to check that parent of your candidate > is root).
I'm doing IS_ROOT(parent) to check that parent of dentry is root.
> BTW, *any* filesystem may be mounted at several places at once. Moreover, > different subtrees of the same fs may be found at different mountpoints.
Yes. I know.
> IIRC, > back when "pathname-based" checks had been discussed, their proponents said > that they don't care if rules for different instances were inconsistent and > that it's OK to have them covered sepately, as long as you default to giving > lower permissions to unrecognized ones. Why is procfs an exception?
Because procfs redirects /proc/self to /proc/PID using symlink when the userspace accesses information of current process. This redirection makes it impossible for name based checks to grant only accessing information of current process.
What I want to do is to undo this redirection done by procfs. Undoing this redirection makes it possible for name based checks to grant only accessing information of current process.
Granting /proc/self/ is more secure than granting /proc/*/ if userspace needs to access only information of current process.
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