CVE-2026-63826

01/Description

In the Linux kernel, the following vulnerability has been resolved: fbdev: fix use-after-free in store_modes() store_modes() replaces a framebuffer's modelist with modes from userspace. On success it frees the old modelist with fb_destroy_modelist(). Two fields still point into that freed list. One pointer is fb_display[i].mode, the mode a console is using. fbcon_new_modelist() moves these pointers to the new list. It only does so for consoles still mapped to the framebuffer. An unmapped console is skipped and keeps its stale pointer. Unbinding fbcon, for example, sets con2fb_map[i] to -1 but leaves fb_display[i].mode set. An FBIOPUT_VSCREENINFO ioctl with FB_ACTIVATE_INV_MODE later reaches fbcon_mode_deleted(). That function reads the stale fb_display[i].mode through fb_mode_is_equal(). The read is a use-after-free. The other pointer is fb_info->mode, the current mode. It is set through the mode sysfs attribute. store_modes() does not update fb_info->mode, so it is left pointing into the freed list. show_mode(), the attribute's read handler, dereferences the stale fb_info->mode through mode_string(). The read is a use-after-free. Clear both pointers before freeing the list. Commit a1f305893074 ("fbcon: Set fb_display[i]->mode to NULL when the mode is released") added the helper fbcon_delete_modelist(). It clears every fb_display[i].mode that points into a given list. So far it is called only from the unregister path. Call it from store_modes() too, and set fb_info->mode to NULL.

02/Affected products

linux: linux kernel

03/References6

• git.kernel.org/stable/c/0d35f9f194a858567a21017d69318a51e3a822b9 Patch
• git.kernel.org/stable/c/2c1c805c65fb7dc7524e20376d6987721e73a0b1 Patch
• git.kernel.org/stable/c/3047319e44f1368370f6fa2c04dea2961fb10215 Patch
• git.kernel.org/stable/c/5267eab88fa4c684459504b8be577ad64953b9a6 Patch
• git.kernel.org/stable/c/70f1e000b88cfa8ca3fd7f4d082647fc089a7769 Patch
• git.kernel.org/stable/c/c6765f39ed27014ff877b00a2efa494233404e17 Patch