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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