dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-89996
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-09-16 11:17:10 UTC
Updated2026-09-16 11:17:10 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: dma-buf: dma-heap: don't publish fd before copy_to_user() succeeds DMA_HEAP_IOCTL_ALLOC allocates a dma-buf and installs an fd into the caller's fd table via dma_buf_fd() -> fd_install() before dma_heap_ioctl() copies the result back to userspace. If the trailing copy_to_user() fails, userspace never learns the fd number, but the fd (and the underlying dma-buf reference) are already visible to other threads in the same process and are leaked for the lifetime of the process. The obvious "close it on the failure path" fix is unsafe: once fd_install() has run, another thread can already dup() the fd, send it via SCM_RIGHTS, or close() it and let its number be reused, so a subsequent close_fd() from the ioctl path can operate on an unrelated file. This was pointed out by Christian König on v1 [1]. Restructure the allocation path so that fd_install() is the last, unfailable step of a successful ioctl: 1. heap->ops->allocate() creates the dma_buf. 2. get_unused_fd_flags() reserves an fd number in the caller's fd table without publishing it, so no other thread can observe it. 3. copy_to_user() delivers the fd number to userspace; on failure the fd is returned with put_unused_fd() and the dma_buf reference is dropped with dma_buf_put(), leaving no user- visible state behind. 4. dma_buf_fd_install() publishes the fd and emits the trace_dma_buf_fd tracepoint -- from here on the ioctl cannot fail. A new dma_buf_fd_install() helper is introduced in dma-buf.c to wrap fd_install() together with the DMA_BUF_TRACE() call, preserving the export tracing that dma_buf_fd() provides. dma_heap_ioctl_allocate() is refactored to return the struct dma_buf * directly (returning ERR_PTR on failure) so the caller holds the dmabuf reference across steps 3 and 4. The failure at step 3 is easily reachable from userspace: pass a struct dma_heap_allocation_data that lives in a page whose protection is flipped to PROT_READ between copy_from_user() and copy_to_user() (e.g. via mprotect()). Before this change each such ioctl leaks one dmabuf fd; after it, the fd table is unchanged on failure and only /dev/dma_heap/<name> remains open. No UAPI or heap-driver interface change. [1] https://lore.kernel.org/dri-devel/[email protected]/

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected c02a81fba74fe3488ad6b08bfb5a1329005418f8 69d57dbadb27ffd5eef34fd184bab145500cdabc git Not specified
CNA Linux Linux affected c02a81fba74fe3488ad6b08bfb5a1329005418f8 0d4a5d218055db29b50cc07d3d73d27007c2a391 git Not specified
CNA Linux Linux affected c02a81fba74fe3488ad6b08bfb5a1329005418f8 30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0 git Not specified
CNA Linux Linux affected 5.6 Not specified
CNA Linux Linux unaffected 5.6 semver Not specified
CNA Linux Linux unaffected 6.18.52 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.5 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3-rc2 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/69d57dbadb27ffd5eef34fd184bab145500cdabc 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0d4a5d218055db29b50cc07d3d73d27007c2a391 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/30d0aff2c65a277135cfd8ea28fa1ee75e0ea4e0 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

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