Re: kernel BUG at fs/inode.c:LINE!
From: Ian Kent
Date: Tue Dec 18 2018 - 05:42:45 EST
On Mon, 2018-12-17 at 07:21 +0000, Al Viro wrote:
> On Sun, Dec 16, 2018 at 10:11:04PM -0800, syzbot wrote:
> > Hello,
> >
> > syzbot found the following crash on:
> >
> > HEAD commit: d14b746c6c1c Add linux-next specific files for 20181214
> > git tree: linux-next
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13706347400000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=1da6d2d18f803140
> > dashboard link: https://syzkaller.appspot.com/bug?extid=5399ed0832693e29f392
> > compiler: gcc (GCC) 8.0.1 20180413 (experimental)
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=101032b3400000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16534063400000
> >
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+5399ed0832693e29f392@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > slab_pre_alloc_hook mm/slab.h:423 [inline]
> > slab_alloc mm/slab.c:3365 [inline]
> > kmem_cache_alloc+0x2c4/0x730 mm/slab.c:3539
> > __d_alloc+0xc8/0xb90 fs/dcache.c:1599
> > ------------[ cut here ]------------
> > kernel BUG at fs/inode.c:1566!
> > d_alloc_anon fs/dcache.c:1698 [inline]
> > d_make_root+0x43/0xc0 fs/dcache.c:1885
> > autofs_fill_super+0x6f1/0x1c30 fs/autofs/inode.c:273
>
> Huh? BUG is in iput(), AFAICS, so the stack trace is rather misreported.
> iput() can be called by d_make_root(), provided that dentry allocation
> fails. So the most straightforward interpretation would be that we
> had an allocation failure (injected?), followed by iput() of the inode
> passed to d_make_root(). Which happened to find I_CLEAR in ->i_state
> of that inode somehow, which should be impossible short of seriously
> buggered inode refcounting somewhere - the inode has just been returned
> by new_inode(), which clears i_state, and it would have to have passed
> clear_inode() (i.e. has been through inode eviction) since then...
Sorry Al, that's my bad.
See https://www.ozlabs.org/~akpm/mmotm/broken-out/autofs-fix-possible-inode-leak-in-autofs_fill_super.patch
I think this will fix it, I'll forward it to Andrew if you agree:
autofs - fix handling of d_make_root() return in autofs_fill_super()
From: Ian Kent <raven@xxxxxxxxxx>
A previous change to handle a possible inode leak in autofs_fill_super()
added an iput() on d_make_root() failure but d_make_root() already puts
the passed in inode on failure.
Reported-by: syzbot+5399ed0832693e29f392@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ian Kent <raven@xxxxxxxxxx>
---
fs/autofs/inode.c | 4 +---
1 file changed, 1 insertion(+), 3 deletions(-)
diff --git a/fs/autofs/inode.c b/fs/autofs/inode.c
index 501833cc49a8..953f76b95172 100644
--- a/fs/autofs/inode.c
+++ b/fs/autofs/inode.c
@@ -271,7 +271,7 @@ int autofs_fill_super(struct super_block *s, void *data, int silent)
}
root = d_make_root(root_inode);
if (!root)
- goto fail_iput;
+ goto fail_ino;
pipe = NULL;
root->d_fsdata = ino;
@@ -347,8 +347,6 @@ int autofs_fill_super(struct super_block *s, void *data, int silent)
fail_dput:
dput(root);
goto fail_free;
-fail_iput:
- iput(root_inode);
fail_ino:
autofs_free_ino(ino);
fail_free: