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] == '\n' ; 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 '\n', 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.
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] == '\n' ; 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 '\n', 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.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
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| Linux | Linux | affected |
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Advisories
No advisories yet.
Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Sun, 19 Jul 2026 15:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | 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] == '\n' ; 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 '\n', 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. | |
| Title | auxdisplay: line-display: fix OOB read on zero-length message_store() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
|
Projects
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MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-07-19T14:55:42.679Z
Reserved: 2026-07-19T07:54:57.023Z
Link: CVE-2026-63949
Vulnrichment
No data.
NVD
No data.
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.