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:
