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| author | Quanmin Yan <yanquanmin1@huawei.com> | 2025-10-10 16:16:59 +0800 |
|---|---|---|
| committer | Helge Deller <deller@gmx.de> | 2025-10-28 22:59:19 +0100 |
| commit | a1f3058930745d2b938b6b4f5bd9630dc74b26b7 (patch) | |
| tree | a8afa1c237bb59ed3087608bcffbbdc10d9d4e04 /include | |
| parent | 18c4ef4e765a798b47980555ed665d78b71aeadf (diff) | |
| download | linux-a1f3058930745d2b938b6b4f5bd9630dc74b26b7.tar.gz linux-a1f3058930745d2b938b6b4f5bd9630dc74b26b7.tar.bz2 linux-a1f3058930745d2b938b6b4f5bd9630dc74b26b7.zip | |
fbcon: Set fb_display[i]->mode to NULL when the mode is released
Recently, we discovered the following issue through syzkaller:
BUG: KASAN: slab-use-after-free in fb_mode_is_equal+0x285/0x2f0
Read of size 4 at addr ff11000001b3c69c by task syz.xxx
...
Call Trace:
<TASK>
dump_stack_lvl+0xab/0xe0
print_address_description.constprop.0+0x2c/0x390
print_report+0xb9/0x280
kasan_report+0xb8/0xf0
fb_mode_is_equal+0x285/0x2f0
fbcon_mode_deleted+0x129/0x180
fb_set_var+0xe7f/0x11d0
do_fb_ioctl+0x6a0/0x750
fb_ioctl+0xe0/0x140
__x64_sys_ioctl+0x193/0x210
do_syscall_64+0x5f/0x9c0
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Based on experimentation and analysis, during framebuffer unregistration,
only the memory of fb_info->modelist is freed, without setting the
corresponding fb_display[i]->mode to NULL for the freed modes. This leads
to UAF issues during subsequent accesses. Here's an example of reproduction
steps:
1. With /dev/fb0 already registered in the system, load a kernel module
to register a new device /dev/fb1;
2. Set fb1's mode to the global fb_display[] array (via FBIOPUT_CON2FBMAP);
3. Switch console from fb to VGA (to allow normal rmmod of the ko);
4. Unload the kernel module, at this point fb1's modelist is freed, leaving
a wild pointer in fb_display[];
5. Trigger the bug via system calls through fb0 attempting to delete a mode
from fb0.
Add a check in do_unregister_framebuffer(): if the mode to be freed exists
in fb_display[], set the corresponding mode pointer to NULL.
Signed-off-by: Quanmin Yan <yanquanmin1@huawei.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>
Cc: stable@vger.kernel.org
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/fbcon.h | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/fbcon.h b/include/linux/fbcon.h index 81f0e698acbf..f206370060e1 100644 --- a/include/linux/fbcon.h +++ b/include/linux/fbcon.h @@ -18,6 +18,7 @@ void fbcon_suspended(struct fb_info *info); void fbcon_resumed(struct fb_info *info); int fbcon_mode_deleted(struct fb_info *info, struct fb_videomode *mode); +void fbcon_delete_modelist(struct list_head *head); void fbcon_new_modelist(struct fb_info *info); void fbcon_get_requirement(struct fb_info *info, struct fb_blit_caps *caps); @@ -38,6 +39,7 @@ static inline void fbcon_suspended(struct fb_info *info) {} static inline void fbcon_resumed(struct fb_info *info) {} static inline int fbcon_mode_deleted(struct fb_info *info, struct fb_videomode *mode) { return 0; } +static inline void fbcon_delete_modelist(struct list_head *head) {} static inline void fbcon_new_modelist(struct fb_info *info) {} static inline void fbcon_get_requirement(struct fb_info *info, struct fb_blit_caps *caps) {} |