On 2023/9/9 17:48, Masami Hiramatsu (Google) wrote:

On Sat, 9 Sep 2023 15:28:16 +0800
Jinjie Ruan [off-list ref] wrote:

quoted

Inject fault while probing btrfs.ko, if kstrdup() fails in
eventfs_prepare_ef() in eventfs_add_dir(), it will return ERR_PTR
to assign file->ef. But the eventfs_remove() check NULL in
trace_module_remove_events(), which causes the below NULL
pointer dereference.

As both Masami and Steven suggest, use IS_ERR_OR_NULL() to
check ef in eventfs_remove_rec(), and fix the same issue
in eventfs_remove().

 Could not create tracefs 'raid56_write' directory
 Btrfs loaded, zoned=no, fsverity=no
 Unable to handle kernel NULL pointer dereference at virtual address 000000000000001c
 Mem abort info:
   ESR = 0x0000000096000004
   EC = 0x25: DABT (current EL), IL = 32 bits
   SET = 0, FnV = 0
   EA = 0, S1PTW = 0
   FSC = 0x04: level 0 translation fault
 Data abort info:
   ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
   CM = 0, WnR = 0, TnD = 0, TagAccess = 0
   GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
 user pgtable: 4k pages, 48-bit VAs, pgdp=0000000102544000
 [000000000000001c] pgd=0000000000000000, p4d=0000000000000000
 Internal error: Oops: 0000000096000004 [#1] PREEMPT SMP
 Dumping ftrace buffer:
    (ftrace buffer empty)
 Modules linked in: btrfs(-) libcrc32c xor xor_neon raid6_pq cfg80211 rfkill 8021q garp mrp stp llc ipv6 [last unloaded: btrfs]
 CPU: 15 PID: 1343 Comm: rmmod Tainted: G                 N 6.5.0+ #40
 Hardware name: linux,dummy-virt (DT)
 pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : eventfs_remove_rec+0x24/0xc0
 lr : eventfs_remove+0x68/0x1d8
 sp : ffff800082d63b60
 x29: ffff800082d63b60 x28: ffffb84b80ddd00c x27: ffffb84b3054ba40
 x26: 0000000000000002 x25: ffff800082d63bf8 x24: ffffb84b8398e440
 x23: ffffb84b82af3000 x22: dead000000000100 x21: dead000000000122
 x20: ffff800082d63bf8 x19: fffffffffffffff4 x18: ffffb84b82508820
 x17: 0000000000000000 x16: 0000000000000000 x15: 000083bc876a3166
 x14: 000000000000006d x13: 000000000000006d x12: 0000000000000000
 x11: 0000000000000001 x10: 00000000000017e0 x9 : 0000000000000001
 x8 : 0000000000000000 x7 : 0000000000000000 x6 : ffffb84b84289804
 x5 : 0000000000000000 x4 : 9696969696969697 x3 : ffff33a5b7601f38
 x2 : 0000000000000000 x1 : ffff800082d63bf8 x0 : fffffffffffffff4
 Call trace:
  eventfs_remove_rec+0x24/0xc0
  eventfs_remove+0x68/0x1d8
  remove_event_file_dir+0x88/0x100
  event_remove+0x140/0x15c
  trace_module_notify+0x1fc/0x230
  notifier_call_chain+0x98/0x17c
  blocking_notifier_call_chain+0x4c/0x74
  __arm64_sys_delete_module+0x1a4/0x298
  invoke_syscall+0x44/0x100
  el0_svc_common.constprop.1+0x68/0xe0
  do_el0_svc+0x1c/0x28
  el0_svc+0x3c/0xc4
  el0t_64_sync_handler+0xa0/0xc4
  el0t_64_sync+0x174/0x178
 Code: 5400052c a90153b3 aa0003f3 aa0103f4 (f9401400)
 ---[ end trace 0000000000000000 ]---
 Kernel panic - not syncing: Oops: Fatal exception
 SMP: stopping secondary CPUs
 Dumping ftrace buffer:
    (ftrace buffer empty)
 Kernel Offset: 0x384b00c00000 from 0xffff800080000000
 PHYS_OFFSET: 0xffffcc5b80000000
 CPU features: 0x88000203,3c020000,1000421b
 Memory Limit: none
 Rebooting in 1 seconds..

Fixes: 5bdcd5f5331a ("eventfs: Implement removal of meta data from eventfs")
Signed-off-by: Jinjie Ruan <redacted>
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Suggested-by: Steven Rostedt <rostedt@goodmis.org>
---
v2:
- Use IS_ERR_OR_NULL() to check instead of IS_ERR() as suggested.
- Update the commit message.
---
 fs/tracefs/event_inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/tracefs/event_inode.c b/fs/tracefs/event_inode.c
index 237c6f370ad9..c354b6013881 100644
--- a/fs/tracefs/event_inode.c
+++ b/fs/tracefs/event_inode.c

@@ -693,7 +693,7 @@ static void eventfs_remove_rec(struct eventfs_file *ef, struct list_head *head,
 {
 	struct eventfs_file *ef_child;
 
-	if (!ef)
+	if (IS_ERR_OR_NULL(ef))

Sorry, I think `ef` must not be an error value because in between the allocation
and this removing, some code can accidentary access it because it is not NULL.

I think the allocator must set NULL, if it's not, it should be warned.

if (!ef || WARN_ON_ONCE(IS_ERR(ef)))
	return;

Of course this still cause a warning, so fix the eventfs_add_dir() too.
(But fixing the eventfs_add_dir() will remove the error, we may not need
this WARN_ON_ONCE() here.)
Or, any other path did you find which sets ef=ERR_PTR(err)?

Not found so far.

Thanks,

quoted

 		return;
 	/*
 	 * Check recursion depth. It should never be greater than 3:

@@ -730,7 +730,7 @@ void eventfs_remove(struct eventfs_file *ef)
 	struct dentry *dentry_list = NULL;
 	struct dentry *dentry;
 
-	if (!ef)
+	if (IS_ERR_OR_NULL(ef))
 		return;
 
 	mutex_lock(&eventfs_mutex);

-- 
2.34.1