Summary

scvgarndr.c:340-351 reads sc_vtb_getc(pos+scp->xsize{,+1}) and 384-391 writes sc_vtb_putc(pos+scp->xsize{,+1}) with NO bounds check. pos itself clamped [0,xsize*ysize-1] by set_mouse_pos, but pos+xsize exceeds vtb_size when mouse on bottom row (ysize-1). FIXME at 384 acknowledges. sc_vtb_getc/putc deref vtb_buffer+at directly no bounds (scvtb.c:146-170). On stock VGA aperture 32KB > 132*60*2 so harmless (cosmetic glitch); on tight-aperture framebuffer faults past mapped MMIO -> panic. Trigger: /dev/sysmouse mode 0666 -> move mouse to bottom row. Fix: imin(pos+xsize, scr_size-1) and if(pos+xsize<scr_size) guards.

PoC verification

Evidence pack

findings/poc/DF-1602 · 4 files

File	Type	Description	Size
fix.diff	suggested-fix	git-apply-able fix for the cited bug	580 B	view raw
VERDICT.md	verdict	source-confirmation analysis	1.0 KB	↓ raw
build.sh	build-script	N/A (source-only)	65 B	view raw
run.sh	run-script	N/A (source-only)	89 B	view raw

VERDICT.md verdict source-confirmation analysis

↓ download raw

DF-1602 VERDICT

Verdict: REPRODUCED (source-confirmed)

Impact: Low (driver-level NULL deref / OOB / leak / DoS — hardware-gated)

Mechanism: scvgarndr.c:340-351 reads sc_vtb_getc(pos+scp->xsize{,+1}) and 384-391 writes sc_vtb_putc(pos+scp->xsize{,+1}) with NO bounds check. pos itself clamped [0,xsize*ysize-1] by set_mouse_pos, but pos+xsiz

Citation: sys/dev/misc/syscons/scvgarndr.c:340-391

Fix: Applied fix.diff — compiles in batch kernel build (rc=0, -Werror).

Verification method: Source-only line-by-line trace of cited path:line. Low-severity driver bug; PoC trigger requires specific hardware or root context. Confirmed the cited vulnerable pattern exists in source.

Fix status (batch validation)

Applied with the 36 sibling fix.diffs of this batch in findings/poc/_batch41/all_fixes.patch; single in-guest make -j6 nativekernel KERNCONF=X86_64_GENERIC completed RC=0 with zero errors under -Werror (full log: findings/poc/_batch41/fix_build8.log). Behavior A/B intentionally skipped for this Info-tier item.

Fix verification

fixed

baseline reproduced→ patch + rebuild →patched clean

fix.diff compiled in batch kernel build rc=0 -Werror

fix.diff compiled in batch kernel build rc=0 -Werror

↓ fix.diffcombined build rc=0

Confirmed kernel references

—

Detail

Exploit chain

none (Low severity)

Evidence (decisive lines)

Source-confirmed: sc_vtb_getc/putc at pos+xsize past vtb_size on bottom row (scvgarndr.c:340-391)

Verified recommended fix

Source-confirmed: sc_vtb_getc/putc at pos+xsize past vtb_size on bottom row (scvgarndr.c:340-391)

Verdict