Messages in this thread | | | Date | Thu, 06 Mar 2014 11:02:00 -0500 | From | Sasha Levin <> | Subject | Re: fs: gpf in simple_setattr |
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On 03/05/2014 07:45 AM, Jan Kara wrote: > On Tue 04-03-14 19:00:32, Sasha Levin wrote: >> On 03/03/2014 04:40 PM, Jan Kara wrote: >>> On Sat 01-03-14 15:05:21, Sasha Levin wrote: >>>>> ping again? >>>>> >>>>> I've been working on it, but don't see an obvious issue. >>>>> >>>>> It does look like an access to invalid memory easily doable from >>>>> userspace, so it should probably get fixed soon... >>> Hum, can you maybe dump the name in dentry passed to simple_setattr()? Or >>> maybe even the whole path using dentry_path() (but not sure if that will >>> be workable on half-torn-down fs)? Maybe it will give us a hint at which >>> filesystem to look... >> >> It's just garbage, this is why I'm having a hard time making any progress with >> this bug. > OK, but that is strange because we hold a reference to the dentry so > noone should free it. So dentry->d_name should be valid... Is the rest of > the dentry also garbage? E.g. does dentry->d_inode still point to the inode > we call __mark_inode_dirty() on? Is dentry->d_sb == dentry->d_inode->i_sb? > Also if the inode isn't completely garbage, we can maybe infer something > from inode->i_op - that should point to some statically allocated > operations struct so we should be able to guess fs type from that.
It's actually pretty tricky. This issue being a race makes catching it at the right time difficult.
I've tried catching it in simple_setattr() before calling mark_inode_dirty() by testing for the poison values inside inode, but they seem to be perfectly fine there and still show up as bad within mark_inode_dirty().
Then I tried trapping it inside mark_inode_dirty(), but at that point I usually get garbage inside inode, and have no way to go back to dentry.
Right now I'm just trying to dump everything that goes through simple_setattr() in hopes that I could easily figure out what went wrong by looking at the log, but that just stops the bug from reproducing.
Thanks, Sasha
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