Hello,
This series contains patches suggested by Daniel Vetter to fix a use-after-free error in the fb_release() function, due a fb_info associated with a fbdev being freed too early while a user-space process still has the fbdev dev node opened.
That is caused by a wrong management of the struct fb_info lifetime in drivers, but the fbdev core can also be made more resilient about it an leak
This can easily be reproduced with the simplefb driver doing the following:
$ cat < /dev/fb0 & $ echo simple-framebuffer.0 > /sys/bus/platform/drivers/simple-framebuffer/unbind $ kill %1
[ 257.490471] ------------[ cut here ]------------ ... [ 257.495125] refcount_t: underflow; use-after-free. [ 257.495222] WARNING: CPU: 0 PID: 975 at lib/refcount.c:28 refcount_warn_saturate+0xf4/0x144 ... [ 257.637482] pstate: 80400005 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--) [ 257.644441] pc : refcount_warn_saturate+0xf4/0x144 [ 257.649226] lr : refcount_warn_saturate+0xf4/0x144 [ 257.654009] sp : ffff80000a06bbf0 [ 257.657315] x29: ffff80000a06bbf0 x28: 000000000000000a x27: 000000000000000a [ 257.664448] x26: 0000000000000000 x25: ffff470b88c6a180 x24: 000000000000000a [ 257.671581] x23: ffff470b81706480 x22: ffff470b808c2160 x21: ffff470b8922ba20 [ 257.678713] x20: ffff470b891f5810 x19: ffff470b891f5800 x18: ffffffffffffffff [ 257.685846] x17: 3a725f7463656a62 x16: ffffbb18c6465fd4 x15: 0720072007200720 [ 257.692978] x14: 0720072d072d072d x13: 0a2e656572662d72 x12: 657466612d657375 [ 257.700110] x11: 203b776f6c667265 x10: 646e75203a745f74 x9 : ffffbb18c58f6c90 [ 257.707242] x8 : 75203b776f6c6672 x7 : 65646e75203a745f x6 : 0000000000000001 [ 257.714373] x5 : ffff470bff8ec418 x4 : 0000000000000000 x3 : 0000000000000027 [ 257.721506] x2 : 0000000000000000 x1 : 0000000000000027 x0 : 0000000000000026 [ 257.728638] Call trace: [ 257.731075] refcount_warn_saturate+0xf4/0x144 [ 257.735513] put_fb_info+0x70/0x7c [ 257.738916] fb_release+0x60/0x74 [ 257.742225] __fput+0x88/0x240 [ 257.745276] ____fput+0x1c/0x30 [ 257.748410] task_work_run+0xc4/0x21c [ 257.752066] do_exit+0x170/0x370 [ 257.755288] do_group_exit+0x40/0xb4 [ 257.758858] get_signal+0x8e0/0x90c [ 257.762339] do_signal+0x1a0/0x280 [ 257.765733] do_notify_resume+0xc8/0x390 [ 257.769650] el0_da+0xe8/0xf0 [ 257.772613] el0t_64_sync_handler+0xe8/0x130 [ 257.776877] el0t_64_sync+0x190/0x194 [ 257.780534] ---[ end trace 0000000000000000 ]---
Patch #1 adds a WARN_ON() to framebuffer_release() to prevent the use-after-free to happen.
Patch #2, #3 and #4 fix the simplefb, efifb and vesafb drivers respectively, to free the resources at the correct place.
Changes in v3: - Add Fixes: tag (Daniel Vetter). - Include in commit message a note that drivers are still broken but at least reverts to the previous behavior (Daniel Vetter). - Only move framebuffer_release() and don't do any other change (Daniel Vetter).
Changes in v2: - Also do the change for vesafb (Thomas Zimmermann).
Daniel Vetter (1): fbdev: Prevent possible use-after-free in fb_release()
Javier Martinez Canillas (3): fbdev: simplefb: Cleanup fb_info in .fb_destroy rather than .remove fbdev: efifb: Cleanup fb_info in .fb_destroy rather than .remove fbdev: vesafb: Cleanup fb_info in .fb_destroy rather than .remove
drivers/video/fbdev/core/fbsysfs.c | 4 ++++ drivers/video/fbdev/efifb.c | 9 ++++++++- drivers/video/fbdev/simplefb.c | 8 +++++++- drivers/video/fbdev/vesafb.c | 8 +++++++- 4 files changed, 26 insertions(+), 3 deletions(-)