PT-2026-61266 · Linux · Linux

CVE-2026-63949

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Published

2026-07-19

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Updated

2026-07-19

None

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In the Linux kernel, the following vulnerability has been resolved:
auxdisplay: line-display: fix OOB read on zero-length message store()
linedisp display() unconditionally reads msg[count - 1] before checking whether count is zero, so a write of zero bytes to the message sysfs attribute hits msg[-1]:
write(fd, "", 0);

-> message store(..., buf, count=0)
  -> linedisp display(linedisp, buf, count=0)
   -> msg[count - 1] == '
' ; OOB read
The kernfs write buffer for that store is a 1-byte allocation (kernfs fop write iter() does kmalloc(len + 1) with len == 0), so msg[-1] is a 1-byte read before the slab object. On a KASAN-enabled kernel this trips an out-of-bounds report and panics; on stock kernels it silently reads adjacent slab data and, if that byte happens to be ' ', the following count-- wraps ssize t 0 to -1 and is then passed to kmemdup nul().
linedisp display() is reached from the message store() sysfs callback (drivers/auxdisplay/line-display.c message attribute, mode 0644) and from the in-tree initial-message setup with count == -1, so the OOB path is only userspace-triggerable via zero-byte writes; vfs write() does not short-circuit on count == 0 and kernfs fop write iter() dispatches the store callback regardless.
Guard the trailing-newline trim with a count check. The existing if (!count) block then takes the clear-display path unchanged.
Affects every auxdisplay driver that registers via linedisp register() / linedisp attach(): ht16k33, max6959, img-ascii-lcd, seg-led-gpio.
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Related Identifiers

CVE-2026-63949

Affected Products

Linux