Fix framebuffer pseudo palette setup

[Shaoen-Lin]

Function vcam_fb_setcolreg() writes TRUECOLOR entries through info->pseudo_palette, but vcamfb_init() initializes that pointer to NULL. A colormap update can therefore dereference a NULL pseudo_palette.

Add a 16-entry pseudo palette to the framebuffer private data and point info->pseudo_palette to it during initialization.

[cubic-dev-ai]

No issues found across 1 file

_{Re-trigger cubic}

[Shaoen-Lin]

Test case to reproduce:

This test verifies that FBIOPUTCMAP reaches vcam_fb_setcolreg().
Before the fix, info->pseudo_palette was NULL, so updating the
colormap triggered a NULL pointer dereference.

sudo insmod ./vcam.ko
sudo /tmp/fb-putcmap /dev/fb1
echo $?
sudo rmmod vcam

Output before fix:

BUG: kernel NULL pointer dereference, address: 0000000000000000
Oops: Oops: 0002 [#1] PREEMPT SMP NOPTI
RIP: 0010:vcam_fb_setcolreg+0xc3/0xe0 [vcam]

Output after fix:

0

Checked dmesg; no BUG, Oops, NULL pointer dereference, KASAN report,
or general protection fault was reported after the patched test.

Also ran the coding style check:

sh .ci/check-format.sh
echo $?

Output:

0

[Shaoen-Lin]

Hi @jserv ,

Sorry for the ping. I have updated this PR with the reproduction steps and testing results.

This PR fixes a possible NULL pointer dereference in vcam_fb_setcolreg() by setting up the framebuffer pseudo_palette properly. I also added the before/after testing results in the PR description.

Could you please take a look when convenient? Thank you!