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Subject[PATCH 1/4] proc: fix NULL ->i_fop oops
proc_kill_inodes() can clear ->i_fop in the middle of vfs_readdir resulting in
NULL dereference during "file->f_op->readdir(file, buf, filler)".

The solution is to remove proc_kill_inodes() completely:
a) we don't have tricky modules implementing their tricky readdir hooks which
could keeping this revoke from hell.
b) In a situation when module is gone but PDE still alive, standard readdir
will return only "." and "..", because pde->next was cleared by
remove_proc_entry().
c) the race proc_kill_inode() destined to prevent is not completely fixed, just
race window made smaller, because vfs_readdir() is run without sb_lock held and
without file_list_lock held. Effectively, ->i_fop is cleared at random moment,
which can't fix properly anything.

BUG: unable to handle kernel NULL pointer dereference at virtual address 00000018
printing eip: c1061205 *pdpt = 0000000005b22001 *pde = 0000000000000000
Oops: 0000 [#1] PREEMPT SMP
Modules linked in: foo af_packet ipv6 cpufreq_ondemand loop serio_raw sr_mod k8temp cdrom hwmon amd_rng
Pid: 2033, comm: find Not tainted (2.6.24-rc1-b1d08ac064268d0ae2281e98bf5e82627e0f0c56 #2)
EIP: 0060:[<c1061205>] EFLAGS: 00010246 CPU: 0
EIP is at vfs_readdir+0x47/0x74
EAX: c6b6a780 EBX: 00000000 ECX: c1061040 EDX: c5decf94
ESI: c6b6a780 EDI: fffffffe EBP: c9797c54 ESP: c5decf78
DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
Process find (pid: 2033, ti=c5dec000 task=c64bba90 task.ti=c5dec000)
Stack: c5decf94 c1061040 fffffff7 0805ffbc 00000000 c6b6a780 c1061295 0805ffbc
00000000 00000400 00000000 00000004 0805ffbc 4588eff4 c5dec000 c10026ba
00000004 0805ffbc 00000400 0805ffbc 4588eff4 bfdc6c70 000000dc 0000007b
Call Trace:
[<c1061040>] filldir64+0x0/0xc5
[<c1061295>] sys_getdents64+0x63/0xa5
[<c10026ba>] sysenter_past_esp+0x5f/0x85
=======================
Code: 49 83 78 18 00 74 43 8d 6b 74 bf fe ff ff ff 89 e8 e8 b8 c0 12 00 f6 83 2c 01 00 00 10 75 22 8b 5e 10 8b 4c 24 04 89 f0 8b 14 24 <ff> 53 18 f6 46 1a 04 89 c7 75 0b 8b 56 0c 8b 46 08 e8 c8 66 00
EIP: [<c1061205>] vfs_readdir+0x47/0x74 SS:ESP 0068:c5decf78
Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
---
fs/proc/generic.c | 37 -------------------------------------
fs/proc/internal.h | 2 --
fs/proc/root.c | 2 +-
3 files changed, 1 insertion(+), 40 deletions(-)
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -544,41 +544,6 @@ static int proc_register(struct proc_dir_entry * dir, struct proc_dir_entry * dp
return 0;
}

-/*
- * Kill an inode that got unregistered..
- */
-static void proc_kill_inodes(struct proc_dir_entry *de)
-{
- struct list_head *p;
- struct super_block *sb;
-
- /*
- * Actually it's a partial revoke().
- */
- spin_lock(&sb_lock);
- list_for_each_entry(sb, &proc_fs_type.fs_supers, s_instances) {
- file_list_lock();
- list_for_each(p, &sb->s_files) {
- struct file *filp = list_entry(p, struct file,
- f_u.fu_list);
- struct dentry *dentry = filp->f_path.dentry;
- struct inode *inode;
- const struct file_operations *fops;
-
- if (dentry->d_op != &proc_dentry_operations)
- continue;
- inode = dentry->d_inode;
- if (PDE(inode) != de)
- continue;
- fops = filp->f_op;
- filp->f_op = NULL;
- fops_put(fops);
- }
- file_list_unlock();
- }
- spin_unlock(&sb_lock);
-}
-
static struct proc_dir_entry *proc_create(struct proc_dir_entry **parent,
const char *name,
mode_t mode,
@@ -753,8 +718,6 @@ void remove_proc_entry(const char *name, struct proc_dir_entry *parent)
continue_removing:
if (S_ISDIR(de->mode))
parent->nlink--;
- if (!S_ISREG(de->mode))
- proc_kill_inodes(de);
de->nlink = 0;
WARN_ON(de->subdir);
if (!atomic_read(&de->count))
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -78,5 +78,3 @@ static inline int proc_fd(struct inode *inode)
{
return PROC_I(inode)->fd;
}
-
-extern struct file_system_type proc_fs_type;
--- a/fs/proc/root.c
+++ b/fs/proc/root.c
@@ -98,7 +98,7 @@ static void proc_kill_sb(struct super_block *sb)
put_pid_ns(ns);
}

-struct file_system_type proc_fs_type = {
+static struct file_system_type proc_fs_type = {
.name = "proc",
.get_sb = proc_get_sb,
.kill_sb = proc_kill_sb,
-
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