From 5a622f2d0f86b316b07b55a4866ecb5518dd1cf7 Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Tue, 4 Dec 2007 23:45:28 -0800 Subject: proc: fix proc_dir_entry refcounting Creating PDEs with refcount 0 and "deleted" flag has problems (see below). Switch to usual scheme: * PDE is created with refcount 1 * every de_get does +1 * every de_put() and remove_proc_entry() do -1 * once refcount reaches 0, PDE is freed. This elegantly fixes at least two following races (both observed) without introducing new locks, without abusing old locks, without spreading lock_kernel(): 1) PDE leak remove_proc_entry de_put ----------------- ------ [refcnt = 1] if (atomic_read(&de->count) == 0) if (atomic_dec_and_test(&de->count)) if (de->deleted) /* also not taken! */ free_proc_entry(de); else de->deleted = 1; [refcount=0, deleted=1] 2) use after free remove_proc_entry de_put ----------------- ------ [refcnt = 1] if (atomic_dec_and_test(&de->count)) if (atomic_read(&de->count) == 0) free_proc_entry(de); /* boom! */ if (de->deleted) free_proc_entry(de); BUG: unable to handle kernel paging request at virtual address 6b6b6b6b printing eip: c10acdda *pdpt = 00000000338f8001 *pde = 0000000000000000 Oops: 0000 [#1] PREEMPT SMP Modules linked in: af_packet ipv6 cpufreq_ondemand loop serio_raw psmouse k8temp hwmon sr_mod cdrom Pid: 23161, comm: cat Not tainted (2.6.24-rc2-8c0863403f109a43d7000b4646da4818220d501f #4) EIP: 0060:[] EFLAGS: 00210097 CPU: 1 EIP is at strnlen+0x6/0x18 EAX: 6b6b6b6b EBX: 6b6b6b6b ECX: 6b6b6b6b EDX: fffffffe ESI: c128fa3b EDI: f380bf34 EBP: ffffffff ESP: f380be44 DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068 Process cat (pid: 23161, ti=f380b000 task=f38f2570 task.ti=f380b000) Stack: c10ac4f0 00000278 c12ce000 f43cd2a8 00000163 00000000 7da86067 00000400 c128fa20 00896b18 f38325a8 c128fe20 ffffffff 00000000 c11f291e 00000400 f75be300 c128fa20 f769c9a0 c10ac779 f380bf34 f7bfee70 c1018e6b f380bf34 Call Trace: [] vsnprintf+0x2ad/0x49b [] vscnprintf+0x14/0x1f [] vprintk+0xc5/0x2f9 [] handle_fasteoi_irq+0x0/0xab [] do_IRQ+0x9f/0xb7 [] preempt_schedule_irq+0x3f/0x5b [] need_resched+0x1f/0x21 [] printk+0x1b/0x1f [] de_put+0x3d/0x50 [] proc_delete_inode+0x38/0x41 [] proc_delete_inode+0x0/0x41 [] generic_delete_inode+0x5e/0xc6 [] iput+0x60/0x62 [] d_kill+0x2d/0x46 [] dput+0xdc/0xe4 [] __fput+0xb0/0xcd [] filp_close+0x48/0x4f [] sys_close+0x67/0xa5 [] sysenter_past_esp+0x5f/0x85 ======================= Code: c9 74 0c f2 ae 74 05 bf 01 00 00 00 4f 89 fa 5f 89 d0 c3 85 c9 57 89 c7 89 d0 74 05 f2 ae 75 01 4f 89 f8 5f c3 89 c1 89 c8 eb 06 <80> 38 00 74 07 40 4a 83 fa ff 75 f4 29 c8 c3 90 90 90 57 83 c9 EIP: [] strnlen+0x6/0x18 SS:ESP 0068:f380be44 Also, remove broken usage of ->deleted from reiserfs: if sget() succeeds, module is already pinned and remove_proc_entry() can't happen => nobody can mark PDE deleted. Dummy proc root in netns code is not marked with refcount 1. AFAICS, we never get it, it's just for proper /proc/net removal. I double checked CLONE_NETNS continues to work. Patch survives many hours of modprobe/rmmod/cat loops without new bugs which can be attributed to refcounting. Signed-off-by: Alexey Dobriyan Cc: "Eric W. Biederman" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/generic.c | 9 ++------- 1 file changed, 2 insertions(+), 7 deletions(-) (limited to 'fs/proc/generic.c') diff --git a/fs/proc/generic.c b/fs/proc/generic.c index 5fccfe2..8d49838 100644 --- a/fs/proc/generic.c +++ b/fs/proc/generic.c @@ -595,6 +595,7 @@ static struct proc_dir_entry *proc_create(struct proc_dir_entry **parent, ent->namelen = len; ent->mode = mode; ent->nlink = nlink; + atomic_set(&ent->count, 1); ent->pde_users = 0; spin_lock_init(&ent->pde_unload_lock); ent->pde_unload_completion = NULL; @@ -692,7 +693,6 @@ void free_proc_entry(struct proc_dir_entry *de) /* * Remove a /proc entry and free it if it's not currently in use. - * If it is in use, we set the 'deleted' flag. */ void remove_proc_entry(const char *name, struct proc_dir_entry *parent) { @@ -741,13 +741,8 @@ continue_removing: parent->nlink--; de->nlink = 0; WARN_ON(de->subdir); - if (!atomic_read(&de->count)) + if (atomic_dec_and_test(&de->count)) free_proc_entry(de); - else { - de->deleted = 1; - printk("remove_proc_entry: %s/%s busy, count=%d\n", - parent->name, de->name, atomic_read(&de->count)); - } break; } spin_unlock(&proc_subdir_lock); -- cgit v1.1