inode->i_private is assigned by a Node pointer only after
registering a new binary format, and it's possible to be NULL if
inode was created by bm_fill_super() (or iput() was called by the
error path in bm_register_write()), and this could result in NULL
pointer dereference when evicting such an inode. e.g. mount
binfmt_misc filesystem then umount it immediately:
mount -t binfmt_misc binfmt_misc /proc/sys/fs/binfmt_misc
umount /proc/sys/fs/binfmt_misc
[ 9379.678259] BUG: unable to handle kernel NULL pointer dereference at 0000000000000013
[ 9379.985952] IP: bm_evict_inode+0x16/0x40 [binfmt_misc]
...
[ 9380.964911] Call Trace:
[ 9380.977633] evict+0xd3/0x1a0
[ 9380.994449] iput+0x17d/0x1d0
[ 9381.010306] dentry_unlink_inode+0xb9/0xf0
[ 9381.034046] __dentry_kill+0xc7/0x170
[ 9381.055145] shrink_dentry_list+0x122/0x280
[ 9381.078908] shrink_dcache_parent+0x39/0x90
[ 9381.103082] do_one_tree+0x12/0x40
[ 9381.122005] shrink_dcache_for_umount+0x2d/0x90
[ 9381.146517] generic_shutdown_super+0x1f/0x120
[ 9381.171644] kill_litter_super+0x29/0x40
[ 9381.193513] deactivate_locked_super+0x43/0x70
[ 9381.219177] deactivate_super+0x45/0x60
[ 9381.240130] cleanup_mnt+0x3f/0x70
[ 9381.259064] __cleanup_mnt+0x12/0x20
[ 9381.279802] task_work_run+0x86/0xa0
[ 9381.299612] exit_to_usermode_loop+0x6d/0x99
[ 9381.323872] syscall_return_slowpath+0xba/0xf0
[ 9381.350464] entry_SYSCALL_64_fastpath+0xa3/0xa
Fix it by making sure Node (e) is not NULL.
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Fixes: 83f918274e4b ("exec: binfmt_misc: shift filp_close(interp_file) from kill_node() to bm_evict_inode()")
Acked-by: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Eryu Guan <eguan@xxxxxxxxxx>
---
v2:
- update commit log as suggested by Oleg
Hi Andrew, could you please help replace the v1 patch in -mm tree with
this v2? The new commit log describes the problem more accurately.
Thanks!
fs/binfmt_misc.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index 2a46762def31..a7c5a9861bef 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -596,7 +596,7 @@ static void bm_evict_inode(struct inode *inode)
{
Node *e = inode->i_private;
- if (e->flags & MISC_FMT_OPEN_FILE)
+ if (e && e->flags & MISC_FMT_OPEN_FILE)
filp_close(e->interp_file, NULL);
clear_inode(inode);
--
2.13.6
