On 2025/3/1 19:51, Alexey Dobriyan wrote:
On Sat, Mar 01, 2025 at 07:46:13AM +0300, Alexey Dobriyan wrote:
On Sat, Mar 01, 2025 at 11:40:24AM +0800, Ye Bin wrote:
There's a issue as follows:
BUG: unable to handle page fault for address: fffffbfff80a702b
Above issue may happen as follows:
rmmod lookup
sys_delete_module
proc_lookup_de
read_lock(&proc_subdir_lock);
pde_get(de);
read_unlock(&proc_subdir_lock);
proc_get_inode(dir->i_sb, de);
mod->exit()
proc_remove
remove_proc_subtree
write_lock(&proc_subdir_lock);
write_unlock(&proc_subdir_lock);
proc_entry_rundown(de);
free_module(mod);
if (S_ISREG(inode->i_mode))
if (de->proc_ops->proc_read_iter)
--> As module is already freed, will trigger UAF
Hey look, vintage 17.5 year old /proc bug.
This just shows how long I didn't ran rmmod test. :-(
To solve above issue there's need to get 'in_use' before use proc_dir_entry
in proc_get_inode().
Fixes: fd5a13f4893c ("proc: add a read_iter method to proc proc_ops")
OK, this is copy of the original sin below.
Fixes: 778f3dd5a13c ("Fix procfs compat_ioctl regression")
This one is.
Let me think a little.
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -644,6 +644,11 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
return inode;
}
+ if (!pde_is_permanent(de) && !use_pde(de)) {
+ pde_put(de);
+ return NULL;
+ }
+
if (de->mode) {
inode->i_mode = de->mode;
inode->i_uid = de->uid;
@@ -677,5 +682,9 @@ struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
} else {
BUG();
}
+
+ if (!pde_is_permanent(de))
+ unuse_pde(de);
+
I can't reproduce. Can you test new patch -- it avoid 2 atomic ops on
common path.
I can provide specific reproduction methods and test results of new fixes.
Reproduction method as follows：
1. Kernel modification adding delay：
diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index a3e22803cddf..31a5d8171259 100644
--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -27,6 +27,7 @@
#include <linux/completion.h>
#include <linux/uaccess.h>
#include <linux/seq_file.h>
+#include <linux/delay.h>
#include "internal.h"
@@ -251,6 +252,13 @@ struct dentry *proc_lookup_de(struct inode *dir,
struct dentry *dentry,
if (de) {
pde_get(de);
read_unlock(&proc_subdir_lock);
+ if (!strcmp("ls", current->comm)) {
+ printk("%s: %s %d will wait de=0x%px name=%pd
remove....\n",
+ __func__, current->comm, current->pid,
de, dentry);
+ mdelay(5 * 1000);
+ printk("%s: %s %d end delay de=0x%px name=%pd
remove....\n",
+ __func__, current->comm, current->pid,
de, dentry);
+ }
inode = proc_get_inode(dir->i_sb, de);
if (!inode)
return ERR_PTR(-ENOMEM);
diff --git a/kernel/module/main.c b/kernel/module/main.c
index 3dbe23098433..0b2488c4bdab 100644
--- a/kernel/module/main.c
+++ b/kernel/module/main.c
@@ -60,6 +60,7 @@
#include <linux/debugfs.h>
#include <linux/execmem.h>
#include <uapi/linux/module.h>
+#include <linux/delay.h>
#include "internal.h"
#define CREATE_TRACE_POINTS
@@ -776,6 +777,9 @@ SYSCALL_DEFINE2(delete_module, const char __user *,
name_user,
goto out;
mutex_unlock(&module_mutex);
+ printk("%s: will wait for ls procfs 2s....\n", __func__);
+ mdelay(2 * 1000);
+ printk("%s: end wait for ls procfs\n", __func__);
/* Final destruction now no one is using it. */
if (mod->exit != NULL)
mod->exit();
@@ -791,6 +795,7 @@ SYSCALL_DEFINE2(delete_module, const char __user *,
name_user,
strscpy(last_unloaded_module.taints, module_flags(mod, buf,
false), sizeof(last_unloaded_module.taints));
free_module(mod);
+ printk("%s: freed module\n", __func__);
/* someone could wait for the module in add_unformed_module() */
wake_up_all(&module_wq);
return 0;
2. Preparing module
test_procfs.c：
#include <linux/file.h>
#include <linux/proc_fs.h>
#include <linux/module.h>
#include <linux/version.h>
struct proc_dir_entry *g_proc_test;
static const struct proc_ops g_proc_test_operations = {};
static int __init test_init(void)
{
g_proc_test = proc_create("test_procfs", 0400, NULL,
&g_proc_test_operations);
return 0;
}
static void __exit test_exit(void)
{
printk("test: will exit\n");
proc_remove(g_proc_test);
printk("test: test proc remove\n");
}
module_init(test_init);
module_exit(test_exit);
MODULE_DESCRIPTION("Test module");
MODULE_LICENSE("GPL");
3. Reproduction procedure：
insmod test_procfs.ko
rmmod test_procfs &
sleep 1
ls /proc/test_procfs
4. Reproduction result：
[root@localhost ~]# insmod test_procfs.ko
[ 106.816730][ T2550] test_procfs: loading out-of-tree module taints
kernel.
[root@localhost ~]# rmmod test_procfs &
[1] 2553
[root@localhost ~]# sleep 1
[ 106.871589][ T2553] __do_sys_delete_module: will wait for ls procfs
2s....
[root@localhost ~]# ls /proc/test_procfs
[ 107.898489][ T2556] proc_lookup_de: ls 2556 will wait
de=0xffff8881136bb900 name=test_procfs remove....
[ 108.876730][ T2553] __do_sys_delete_module: end wait for ls procfs
[ 108.877177][ T2553] test: will exit
[ 108.877430][ T2553] test: test proc remove
[ 108.897238][ T2553] __do_sys_delete_module: freed module
[ 112.903812][ T2556] proc_lookup_de: ls 2556 end delay
de=0xffff8881136bb900 name=test_procfs remove....
[ 112.904967][ T2556] BUG: unable to handle page fault for address:
fffffbfff80bb01b
[ 112.906801][ T2556] #PF: supervisor read access in kernel mode
[ 112.908180][ T2556] #PF: error_code(0x0000) - not-present page
[ 112.909534][ T2556] PGD 817fc4067 P4D 817fc4067 PUD 817fc0067 PMD
102ebb067 PTE 0
[ 112.911272][ T2556] Oops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI
[ 112.912648][ T2556] CPU: 28 UID: 0 PID: 2556 Comm: ls Tainted: G
OE
6.14.0-rc4-next-20250228-862.14.0.6.x86_64-00030-gd76eeb7f22fa #110
[ 112.915724][ T2556] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
[ 112.917124][ T2556] Hardware name: QEMU Standard PC (i440FX + PIIX,
1996), BIOS 1.15.0-1 04/01/2014
[ 112.919182][ T2556] RIP: 0010:proc_get_inode+0x302/0x6e0
[ 112.920475][ T2556] Code: 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 cf
03 00 00 48 b8 00 00 00 00 00 fc ff df 48 8b 5d 30 48 8d 7b 18 48 89 fa
48 c1 ea 03 <808
[ 112.924874][ T2556] RSP: 0018:ffff88812c157998 EFLAGS: 00010a06
[ 112.926288][ T2556] RAX: dffffc0000000000 RBX: ffffffffc05d80c0 RCX:
0000000000000007
[ 112.928094][ T2556] RDX: 1ffffffff80bb01b RSI: 0000000000000001 RDI:
ffffffffc05d80d8
[ 112.929908][ T2556] RBP: ffff8881136bb900 R08: 0000000067c50d9b R09:
1ffff1102582af20
[ 112.931755][ T2556] R10: ffffffffa160da07 R11: ffffffff9eb42bb8 R12:
ffff888105bacda0
[ 112.933572][ T2556] R13: ffff888105b38048 R14: ffff8881136bb904 R15:
0000000000000001
[ 112.935372][ T2556] FS: 00007fc41042e840(0000)
GS:ffff88840c1b4000(0000) knlGS:0000000000000000
[ 112.937396][ T2556] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 112.938895][ T2556] CR2: fffffbfff80bb01b CR3: 000000010353c000 CR4:
00000000000006f0
[ 112.940732][ T2556] DR0: 0000000000000000 DR1: 0000000000000000 DR2:
0000000000000000
[ 112.942555][ T2556] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7:
0000000000000400
[ 112.944372][ T2556] Call Trace:
[ 112.945140][ T2556] <TASK>
[ 112.945822][ T2556] ? __die+0x24/0x70
[ 112.946742][ T2556] ? page_fault_oops+0xce/0x120
[ 112.947870][ T2556] ? exc_page_fault+0xb2/0xc0
[ 112.948967][ T2556] ? asm_exc_page_fault+0x26/0x30
[ 112.950055][ T2556] ? inode_init_always_gfp+0x948/0xba0
[ 112.951199][ T2556] ? proc_get_inode+0x302/0x6e0
[ 112.952232][ T2556] ? proc_get_inode+0x3c6/0x6e0
[ 112.953280][ T2556] proc_lookup_de+0x11f/0x2e0
[ 112.954177][ T2556] __lookup_slow+0x187/0x350
[ 112.955065][ T2556] ? __pfx___lookup_slow+0x10/0x10
[ 112.956070][ T2556] ? try_to_unlazy+0x1c4/0x480
[ 112.956984][ T2556] ? lookup_fast+0x230/0x4e0
[ 112.957850][ T2556] ? __pfx_link_path_walk.part.0.constprop.0+0x10/0x10
[ 112.959058][ T2556] walk_component+0x2ab/0x4f0
[ 112.959891][ T2556] path_lookupat+0x120/0x660
[ 112.960711][ T2556] ? __pfx_stack_trace_consume_entry+0x10/0x10
[ 112.961780][ T2556] filename_lookup+0x1cd/0x560
[ 112.962578][ T2556] ? __pfx_filename_lookup+0x10/0x10
[ 112.963458][ T2556] ? set_track_prepare+0x49/0x70
[ 112.964282][ T2556] ? kmem_cache_alloc_noprof+0x2d7/0x360
[ 112.965223][ T2556] ? getname_flags.part.0+0x4b/0x490
[ 112.966075][ T2556] ? __pfx__raw_spin_lock_irqsave+0x10/0x10
[ 112.967003][ T2556] ? __link_object+0x10c/0x1b0
[ 112.967754][ T2556] vfs_statx+0xab/0x150
[ 112.968401][ T2556] ? __pfx_vfs_statx+0x10/0x10
[ 112.969148][ T2556] ? getname_flags.part.0+0xaf/0x490
[ 112.969942][ T2556] __do_sys_newstat+0x95/0x100
[ 112.970648][ T2556] ? __pfx___do_sys_newstat+0x10/0x10
[ 112.971435][ T2556] ? handle_mm_fault+0x172/0x430
[ 112.972160][ T2556] do_syscall_64+0x5f/0x170
[ 112.972831][ T2556] entry_SYSCALL_64_after_hwframe+0x76/0x7e
[ 112.973693][ T2556] RIP: 0033:0x7fc40f2ee895
[ 112.974280][ T2556] Code: e8 60 01 00 00 48 83 c4 18 c3 66 2e 0f 1f
84 00 00 00 00 00 90 83 ff 01 48 89 f0 77 18 48 89 c7 48 89 d6 b8 04 00
00 00 0f 05 <486
[ 112.976839][ T2556] RSP: 002b:00007ffd0107d9f8 EFLAGS: 00000246
ORIG_RAX: 0000000000000004
[ 112.977920][ T2556] RAX: ffffffffffffffda RBX: 00007ffd0107ecb3 RCX:
00007fc40f2ee895
[ 112.978919][ T2556] RDX: 0000000016022110 RSI: 0000000016022110 RDI:
00007ffd0107ecb3
[ 112.979928][ T2556] RBP: 00007ffd0107dda0 R08: 0000000000000000 R09:
0000000016022100
[ 112.980937][ T2556] R10: 00007ffd0107d5c0 R11: 0000000000000246 R12:
00007ffd0107ecb3
[ 112.981932][ T2556] R13: 000000000000000a R14: 0000000016022100 R15:
0000000000000000
[ 112.982887][ T2556] </TASK>
...
[ 112.999566][ T2556] ---[ end Kernel panic - not syncing: Fatal
exception ]---
5. Test results for new patch：
--round 1
[root@localhost ~]# insmod test_procfs.ko
[ 300.997847][ T2641] test_procfs: loading out-of-tree module taints
kernel.
[root@localhost ~]# rmmod test_procfs &
[1] 2644
[root@localhost ~]# sleep 1
[ 301.062858][ T2644] __do_sys_delete_module: will wait for ls procfs
2s....
[root@localhost ~]# ls /proc/test_procfs
[ 302.084609][ T2647] proc_lookup_de: ls 2647 will wait
de=0xffff888122a74000 name=test_procfs remove....
[ 303.066879][ T2644] __do_sys_delete_module: end wait for ls procfs
[ 303.067351][ T2644] test: will exit
[ 303.067624][ T2644] test: test proc remove
[ 303.087512][ T2644] __do_sys_delete_module: freed module
[ 307.088773][ T2647] proc_lookup_de: ls 2647 end delay
de=0xffff888122a74000 name=test_procfs remove....
ls: cannot access /proc/test_procfs: No such file or directory
[1]+ Done rmmod test_procfs
--round 2
[root@localhost ~]#
[root@localhost ~]# insmod test_procfs.ko
[root@localhost ~]# rmmod test_procfs &
[1] 2651
[root@localhost ~]# sleep 1
[ 315.614603][ T2651] __do_sys_delete_module: will wait for ls procfs
2s....
[root@localhost ~]# ls /proc/test_procfs
[ 316.638267][ T2654] proc_lookup_de: ls 2654 will wait
de=0xffff888117ade000 name=test_procfs remove....
[ 317.617933][ T2651] __do_sys_delete_module: end wait for ls procfs
[ 317.618504][ T2651] test: will exit
[ 317.618758][ T2651] test: test proc remove
[ 317.638900][ T2651] __do_sys_delete_module: freed module
[ 321.642678][ T2654] proc_lookup_de: ls 2654 end delay
de=0xffff888117ade000 name=test_procfs remove....
ls: cannot access /proc/test_procfs: No such file or directory
[1]+ Done rmmod test_procfs
If the bug is looking into pde->proc_ops, then don't do it.
Yes. It's a really good idea.
