Hi Am 30.04.22 um 04:57 schrieb Junxiao Chang:
When firmware framebuffer is in use, don't remove its platform device. Or else its fb_info buffer is released by platform remove hook while device is still opened. This introduces use after free issue.
When exactly does this happen? Do you have a reliable way of reproducing it? Best regards Thomas
A kernel panic example:
CPU: 2 PID: 3425 Comm: psplash Tainted: G U W 5.18.0-rc3
Hardware name: Intel Client Platform/ADP-S DDR5 UDIMM CRB
RIP: 0010:native_queued_spin_lock_slowpath+0x1c7/0x210
RSP: 0018:ffffb3a0c0c2fdb0 EFLAGS: 00010206
RAX: 002dc074ff5c0988 RBX: ffff92e987a5d818 RCX: ffff92e989ba9f40
RDX: 0000000000002067 RSI: ffffffff864344f1 RDI: ffffffff8644183c
RBP: ffff92f10f4abd40 R08: 0000000000000001 R09: ffff92e986dc2188
...
Call Trace:
<TASK>
_raw_spin_lock+0x2c/0x30
__mutex_lock.constprop.0+0x175/0x4f0
? _raw_spin_unlock+0x15/0x30
? list_lru_add+0x124/0x160
fb_release+0x1b/0x60
__fput+0x89/0x240
task_work_run+0x59/0x90
do_exit+0x343/0xaf0
do_group_exit+0x2d/0x90
__x64_sys_exit_group+0x14/0x20
do_syscall_64+0x40/0x90
entry_SYSCALL_64_after_hwframe+0x44/0xae
Fixes: 27599aacbaef ("fbdev: Hot-unplug firmware fb devices on forced removal")
Signed-off-by: Junxiao Chang <junxiao.chang@xxxxxxxxx>
Signed-off-by: Lili Li <lili.li@xxxxxxxxx>
---
drivers/video/fbdev/core/fbmem.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/drivers/video/fbdev/core/fbmem.c b/drivers/video/fbdev/core/fbmem.c
index a6bb0e438216..ff9b9830b398 100644
--- a/drivers/video/fbdev/core/fbmem.c
+++ b/drivers/video/fbdev/core/fbmem.c
@@ -1586,7 +1586,9 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
* framebuffer as before without warning.
*/
do_unregister_framebuffer(registered_fb[i]);
- } else if (dev_is_platform(device)) {
+ } else if (dev_is_platform(device) &&
+ refcount_read(®istered_fb[i]->count) == 1) {
+ /* Remove platform device if it is not in use. */
registered_fb[i]->forced_out = true;
platform_device_unregister(to_platform_device(device));
} else {
-- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Ivo Totev
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