kernel/linux.git/drivers/video/fbdev/core/fbcon.c, branch v7.2-rc1

fbcon: fix NULL pointer dereference for a console without vc_data

2026-06-26T13:07:38+00:00

fbcon_new_modelist() runs when a framebuffer's modelist changes. For each console mapped to it with fb_display[i].mode set, it reads vc_cons[i].d and passes the vc_num to fbcon_set_disp(). This assumes a console with a mode set has a vc_data, but it can be NULL. fbcon_set_disp() sets fb_display[i].mode before it checks vc_data, and fbcon_deinit() leaves the mode set after the vc_data is freed. fbcon_new_modelist() then dereferences the NULL vc_data. Keep fb_display[i].mode set only while the console has a vc_data. Check vc_data before setting the mode in fbcon_set_disp(), and clear the mode in fbcon_deinit(). The existing mode check in fbcon_new_modelist() then skips such consoles. Reported-by: syzbot+42525d636f430fd5d983@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=42525d636f430fd5d983 Cc: stable@vger.kernel.org Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Ian Bridges Signed-off-by: Helge Deller

fbdev: fbcon: fix out-of-bounds read in err_out of fbcon_do_set_font()

2026-06-25T16:15:48+00:00

When fbcon_do_set_font() fails (e.g., due to a memory allocation failure inside vc_resize() under heavy memory pressure), it jumps to the `err_out` label to roll back the console state. However, the current rollback logic forgets to restore the `hi_font` state, leading to a severe state machine corruption. Earlier in the function, `set_vc_hi_font()` might be called to change `vc->vc_hi_font_mask` and mutate the screen buffer. If `vc_resize()` subsequently fails, the `err_out` path restores `vc_font.charcount` but entirely skips rolling back the `vc_hi_font_mask` and the screen buffer. This mismatch leaves the terminal in a desynchronized state. Because `vc_hi_font_mask` remains set, the VT subsystem will still accept character indices greater than 255 from userspace and write them to the screen buffer. Subsequent rendering calls (e.g., `fbcon_putcs()`) will then use these inflated indices to access the reverted, 256-character font array, leading to a deterministic out-of-bounds read and potential kernel memory disclosure. Fix this by adding the missing rollback logic for the `hi_font` mask and screen buffer in the error path. Fixes: a5a923038d70 ("fbdev: fbcon: Properly revert changes when vc_resize() failed") Cc: stable@vger.kernel.org Signed-off-by: Mingyu Wang <25181214217@stu.xidian.edu.cn> Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbcon: correct CONFIG_FB_TILEBLITTING macro name in #endif comment

2026-06-09T14:00:11+00:00

A comment in drivers/video/fbdev/core/fbcon.c incorrectly refers to CONFIG_MISC_TILEBLITTING instead of CONFIG_FB_TILEBLITTING. Correct it. Discovered while searching for CONFIG_* symbols referenced in code but not defined in any Kconfig file. Signed-off-by: Ethan Nelson-Moore Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbdev: Do not export fbcon from fbdev

2026-06-09T14:00:11+00:00

There are no callers of fbcon outside fbdev. Move the declarations into the internal header. Signed-off-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbdev: Wrap user-invoked calls to fb_set_var() in helper

2026-06-09T14:00:10+00:00

Handle fbcon during display updates in fb_set_var_from_user(). Check with fbcon if the mode change is possible, update hardware state and finally update fbcon. Update all callers. Only the FBIOPUT_VSCREENINFO ioctl currently does all steps. Other mode-changes callers in sysfs and driver code are missing fbcon-related steps. With the new helper, ps3fb and sh_mobile_lcdcfb no longer maintain fbcon state themselves. Signed-off-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbcon: don't suspend/resume when vc is graphics mode

2026-06-09T14:00:10+00:00

Don't need to do suspend/resume for fbcon in graphic mode. Doing this may cause error, eg: At the beginning, starting the Xorg with single screen and then an external screen was plugged in. After logging out in Xorg, fbdev info may using screen which is connected later on for info always using first connected connector in list in func 'drm_setup_crtcs_fb'. Then, S3 executed, fbcon found that the information did not match and do atomic to switch fb. However, Xorg will not re-bind the crtc fb but continues doing ioctl. At this time, the fb is incorrect. With some modifications by Helge Deller. Signed-off-by: Lu Yao Signed-off-by: Helge Deller

fbcon: Use correct type for vc_resize() return value

2026-06-07T16:25:42+00:00

The return value of vc_resize() is int, but fbcon_set_disp() stores it in an unsigned long variable. While the !ret check happens to work correctly by coincidence (negative values become large positive values), the types should match. Use int instead. Eliminates the following W=3 warning: drivers/video/fbdev/core/fbcon.c: In function 'fbcon_set_disp': drivers/video/fbdev/core/fbcon.c:1494:14: warning: implicit conversion from 'int' to 'unsigned long' [-Wconversion] Fixes: af0db3c1f898 ("fbdev: Fix vmalloc out-of-bounds write in fast_imageblit") Cc: stable@vger.kernel.org # v6.17+ Signed-off-by: Jiacheng Yu Reviewed-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbcon: Put font-rotation state into separate struct

2026-04-07T15:38:07+00:00

Move all temporary state of the font-rotation code into the struct rotated in struct fbcon_par. Protect it with the Kconfig symbol CONFIG_FRAMEBUFFER_CONSOLE_ROTATION. Avoids mixing it up with fbcon's regular state. v2: - fix typos Signed-off-by: Thomas Zimmermann Signed-off-by: Helge Deller

fbcon: Fill cursor mask in helper function

2026-04-07T15:38:07+00:00

Fbcon creates a cursor shape on the fly from the user-configured settings. The logic to create a glyph with the cursor's bitmap mask is duplicated in four places. In the cases that involve console rotation, the implementation further rotates the cursor glyph for displaying. Consolidate all cursor-mask creation in a single helper. Update the callers accordingly. For console rotation, use the glyph helpers to rotate the created cursor glyph to the correct orientation. v2: - fix sparse truncated-bits warning Signed-off-by: Thomas Zimmermann Signed-off-by: Helge Deller

lib/fonts: Store font data for user space with font_data_export()

2026-03-09T14:47:21+00:00

Add font_data_export() and update consoles to use it. The helper font_data_export() is based on code in fbcon_get_font(). It extends the size of a single glyph to match the requested vpitch, which us usually 32 bytes for fonts from user space. Internal fonts have a pitch according to the glyph's height. The implementation of font_data_export() differs in several ways from the original code. The original implementation distinguished between different pitches of the font data. This is not necessary as the pitch is a parameter in the copying. There was also special handling for a font pitch of 3 bytes, which got expanded to 4 bytes (with trailing bits on each scanline). The logic originated from long before git history exists even in the historical tree. So it is not clear why this was implemented. It is not what user space expects. The setfont utitlity loads font with 3-bytes pitches and expects to read such fonts with a 3-byte pitch. For any font width, the font pitch is always the width extended to the next multiple of 8. See [1] for the user-space font-reading code. With the changes to handling the font pitches, font_data_export() replaces the original code's various special cases with a single copying logic. v3: - fix typos (Helge) Signed-off-by: Thomas Zimmermann Link: https://github.com/legionus/kbd/blob/v2.9.0/src/libkfont/kdfontop.c#L73 # [1] Signed-off-by: Helge Deller