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CVE-2026-63910
dma-buf: fix UAF in dma_buf_fd() tracepoint
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/dma-buf. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63910 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Once FD_ADD() returns, the fd is live in the file descriptor table and a thread sharing that table can close() it before DMA_BUF_TRACE() runs. The close drops the last reference, __fput() frees the dma_buf, and the tracepoint then dereferences dmabuf to take dmabuf->name_lock -- slab-use-after-free. Split FD_ADD() back into get_unused_fd_flags() + fd_install() and emit the tracepoint between them. While the fdtable slot is reserved with a NULL file pointer, a racing close() returns -EBADF without entering __fput(), so the dma_buf stays alive across the trace. Same approach as commit 2d76319c4cbb ("dma-buf: fix UAF in dma_buf_put() tracepoint"). This undoes the FD_ADD() conversion done in commit 34dfce523c90 ("dma: convert dma_buf_fd() to FD_ADD()"); FD_ADD() has no place to hook the tracepoint safely.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/dma-buf/dma-buf.c
- What this is
- DMA BUFFER SHARING FRAMEWORKMAINTAINERS section matched on drivers/dma-buf/ · linux-media@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_DMA_SHARED_BUFFER /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_DMA_SHARED_BUFFER
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-07-19 (3 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/dma-buf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 7.0 | 7.0.12 | b569f86e2f8d |
| 7.0 | 7.1 | ead6680f354f |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The UAF is reached only through local syscalls/ioctls (e.g. UDMABUF_CREATE, DMA_HEAP_IOCTL_ALLOC, DRM/videobuf2 buffer export) that call dma_buf_fd(); there is no network or physical-device entry point.
- AC:LAttack complexity, low
- Exploitation requires a race between dma_buf_fd() and close() on a shared fd table, but the attacker controls both threads and can hammer the window concurrently; syzkaller demonstrated reliable triggering without conditions outside attacker control.
- PR:LPrivileges required, low
- An unprivileged local user with access to dma-buf interfaces (udmabuf, dma_heap, DRM render node, or media devices) can reach dma_buf_fd(); syzbot confirmed unprivileged and user-namespace reachability without real root in the init namespace.
- UI:NUser interaction, none
- Exploitation is performed entirely by the attacker's own multi-threaded process issuing ioctls and close() calls; no action by a separate victim user is required.
- S:UScope, unchanged
- Impact is kernel memory corruption and privilege escalation within the same kernel security domain; this is standard local kernel compromise, not a VM escape or IOMMU/DMA boundary bypass.
- C:HConfidentiality impact, high
- The bug is a slab use-after-free on struct dma_buf; the tracepoint dereferences freed memory (name_lock, exp_name, file fields), enabling controlled reuse of freed kmalloc-1k objects for arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- UAF on a kmalloc-1k kernel object with spinlock interaction provides heap corruption primitives that can be developed into arbitrary kernel writes and local privilege escalation.
- A:HAvailability impact, high
- Winning the race causes a confirmed slab-use-after-free in dma_buf_fd() (KASAN/lockdep fault), which can panic or oops the kernel even when not fully exploited for code execution.